This is the MySQL reference manual; it documents MySQL Version 3.23.29-gamma. As MySQL is work in progress, the manual gets updated frequently. There is a very good chance that this version is out of date, unless you are looking at it online. The most recent version of this manual is available at http://www.mysql.com/documentation/ in many different formats. If you have a hard time finding information in the manual, you can try the searchable PHP version at http://www.mysql.com/documentation/manual.php.
MySQL is a very fast, multi-threaded, multi-user, and robust SQL (Structured Query Language) database server.
MySQL is free software. It is licensed with the GNU GENERAL PUBLIC LICENSE http://www.gnu.org/. See section 3 MySQL Licensing and Support.
The MySQL home page provides the latest information about MySQL.
The following list describes some useful sections of the manual:
IMPORTANT:
Reports of errors (often called bugs), as well as questions and comments,
should be sent to the mailing list at mysql@lists.mysql.com.
See section 2.3 How to Report Bugs or Problems.
The mysqlbug script should be used to generate bug reports.
For source distributions, the mysqlbug script can be found in the
`scripts' directory. For binary distributions, mysqlbug can
be found in the `bin' directory.
If you have any suggestions concerning additions or corrections to this manual, please send them to the manual team at (docs@mysql.com).
This is a reference manual; it does not provide general instruction on SQL or relational database concepts. If you want general information about SQL, see section 1.8 General SQL Information and Tutorials. For books that focus more specifically on MySQL, see section 1.4 Books About MySQL.
The official way to pronounce MySQL is ``My Ess Que Ell'' (not MY-SEQUEL). But we try to avoid correcting people who say MY-SEQUEL.
MySQL core values
We want MySQL to be:
MySQL AB and the people of MySQL AB:
This manual is currently available in Texinfo, plain text, Info, HTML,
PostScript, and PDF versions. The primary document is the Texinfo file.
The HTML version is produced automatically using a modified version of
texi2html. The plain text and Info versions are produced with
makeinfo. The Postscript version is produced using texi2dvi
and dvips. The PDF version is produced with pdftex.
This manual is written and maintained by David Axmark, Michael (Monty) Widenius, Jeremy Cole, and Paul DuBois. For other contributors, see section D Credits.
This manual uses certain typographical conventions:
constant
mysqladmin works, invoke it with the
--help option.''
When commands are shown that are meant to be executed by a particular
program, the program is indicated by a prompt shown before the command. For
example, shell> indicates a command that you execute from your login
shell, and mysql> indicates a command that you execute from the
mysql client program:
shell> type a shell command here mysql> type a mysql command here
Shell commands are shown using Bourne shell syntax. If you are using a
csh-style shell, you may need to issue commands slightly differently.
For example, the sequence to set an environment variable and run a command
looks like this in Bourne shell syntax:
shell> VARNAME=value some_command
For csh, you would execute the sequence like this:
shell> setenv VARNAME value shell> some_command
Often, database, table, and column names must be substituted into commands. To
indicate that such substitution is necessary, this manual uses
db_name, tbl_name and col_name. For example, you might
see a statement like this:
mysql> SELECT col_name FROM db_name.tbl_name;
This means that if you were to enter a similar statement, you would supply your own database, table, and column names, perhaps like this:
mysql> SELECT author_name FROM biblio_db.author_list;
SQL statements may be written in uppercase or lowercase. When this manual
shows a SQL statement, uppercase is used for particular keywords if those
keywords are under discussion (to emphasize them) and lowercase is used for
the rest of the statement. For example, you might see the following in a
discussion of the SELECT statement:
mysql> SELECT count(*) FROM tbl_name;
On the other hand, in a discussion of the COUNT() function, the
same statement would be written like this:
mysql> select COUNT(*) from tbl_name;
If no particular emphasis is intended, all keywords are written uniformly in uppercase.
In syntax descriptions, square brackets (`[' and `]') are used to indicate optional words or clauses:
DROP TABLE [IF EXISTS] tbl_name
When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (`|'). When one member from a set of choices may be chosen, the alternatives are listed within square brackets (`[' and `]'):
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
When one member from a set of choices must be chosen, the alternatives are listed within braces (`{' and `}'):
{DESCRIBE | DESC} tbl_name {col_name | wild}
We once started out with the intention of using mSQL to connect to our
tables using our own fast low-level (ISAM) routines. However, after some
testing we came to the conclusion that mSQL was not fast enough nor
flexible enough for our needs. This resulted in a new SQL interface to our
database but with almost the same API interface as mSQL. This API was
chosen to ease porting of third-party code.
The derivation of the name MySQL is not perfectly clear. Our base directory and a large number of our libraries and tools have had the prefix ``my'' for well over 10 years. However, Monty's daughter (some years younger) is also named My. So which of the two gave its name to MySQL is still a mystery, even for us.
While this manual is still the right place for up to date techical information, its primary goal is to contain everything there is to know about MySQL. It is sometimes nice to have a bound book to read in bed or while you travel. Here is a list of books about MySQL and related subjects (in English).
By purchasing a book through these hyperlinks provided herein, you are contributing to the development of MySQL.
MySQL
| Available | Barnes and Noble |
| Publisher | New Riders |
| Author | Paul DuBois |
| Pub Date | 1st Edition December 1999 |
| ISBN | 0735709211 |
| Pages | 800 |
| Price | $49.99 US |
| Downloadable examples |
samp_db.tar.gz
|
| Errata | are available here |
In MySQL, Paul DuBois provides you with a comprehensive guide to
one of the most popular relational database systems. Paul has
contributed to the online documentation for MySQL and is an
active member of the MySQL community. The principal MySQL
developer, Monty Widenius, and a network of his fellow developers
reviewed the manuscript, and provided Paul with the kind of insight
no one else could supply.
Instead of merely giving you a general overview of MySQL, Paul
teaches you how to make the most of its capabilities. Through two
sample database applications that run throughout the book, he
gives you solutions to problems you're sure to face. He helps you
integrate MySQL efficiently with third-party tools, such as PHP
and Perl, enabling you to generate dynamic Web pages through
database queries. He teaches you to write programs that access
MySQL databases, and also provides a comprehensive set of
references to column types, operators, functions, SQL syntax,
MySQL programming, C API, Perl DBI, and PHP API.
MySQL simply gives you the kind of information you won't find
anywhere else.
If you use MySQL, this book provides you with:
DBI and PHP APIs for developing
command-line and Web-based applications
DBI API,
and PHP's MySQL-related functions
MySQL & mSQL
| Available | Barnes and Noble |
| Publisher | O'Reilly |
| Authors | Randy Jay Yarger, George Reese & Tim King |
| Pub Date | 1st Edition July 1999 |
| ISBN | 1-56592-434-7, Order Number: 4347 |
| Pages | 506 |
| Price | $34.95 |
This book teaches you how to use MySQL and mSQL, two popular
and robust database products that support key subsets of SQL on both Linux
and Unix systems. Anyone who knows basic C, Java, Perl, or Python can
write a program to interact with a database, either as a stand-alone
application or through a Web page. This book takes you through the
whole process, from installation and configuration to programming
interfaces and basic administration. Includes ample tutorial
material.
Sams' Teach Yourself MySQL in 21 Days
| Available | Barnes and Noble |
| Publisher | Sams |
| Authors | Mark Maslakowski and Tony Butcher |
| Pub Date | June 2000 |
| ISBN | 0672319144 |
| Pages | 650 |
| Price | $39.99 |
Sams Teach Yourself MySQL in 21 Days is for intermediate Linux users
who want to move into databases. A large share of the audience is Web
developers who need a database to store large amounts of information that can
be retrieved via the Web. Sams' Teach Yourself MySQL in 21 Days is a
practical, step-by-step tutorial. The reader will learn to design and employ
this open source database technology into his/her Web site using practical,
hands-on examples to follow.
E-Commerce Solutions with MySQL
| Available | Barnes and Noble |
| Publisher | Prima Communications, Inc. |
| Authors | N/A |
| Pub Date | January 2000 |
| ISBN | 0761524452 |
| Pages | 500 |
| Price | $39.99 |
No description available.
MySQL and PHP from Scratch
| Available | Barnes and Noble |
| Publisher | Que |
| Authors | N/A |
| Pub Date | September 2000 |
| ISBN | 0789724405 |
| Pages | 550 |
| Price | $34.99 |
This book puts together information on installing, setting up, and
troubleshooting Apache, MySQL, PHP3, and IMP into one complete
volume. You also learn how each piece is part of a whole by learning,
step-by-step, how to create a web-based e-mail system. Learn to run
the equivalent of Active Server Pages (ASP) using PHP3, set up an
e-commerce site using a database and the Apache web server, and create
a data entry system (such as sales, product quality tracking, customer
preferences, etc) that no installation in the PC.
Professional MySQL Programming
| Available | Barnes and Noble |
| Publisher | Wrox Press, Inc. |
| Authors | N/A |
| Pub Date | July 2000 |
| ISBN | 1861004281 |
| Pages | 1000 |
| Price | $49.99 |
No description available.
Professional Linux Programming
| Available | Barnes and Noble |
| Publisher | Wrox Press, Inc. |
| Authors | N/A |
| Pub Date | September 2000 |
| ISBN | 1861003013 |
| Pages | 1155 |
| Price | $47.99 |
In this follow-up to the best-selling Beginning Linux Programming, you
will learn from the authors' real-world knowledge and experience of
developing software for Linux; you'll be taken through the development
of a sample 'DVD Store' application, with 'theme' chapters addressing
different aspects of its implementation. Meanwhile, individual
'take-a-break' chapters cover important topics that go beyond the
bounds of the central theme. All focus on the practical aspects of
programming, showing how crucial it is to choose the right tools for
the job, use them as they should be used, and get things right first
time.
PHP and MySQL Web Development
| Available | Barnes and Noble |
| Publisher | Sams |
| Authors | Luke Welling, Laura Thomson |
| Pub Date | November 2000 |
| ISBN | 0672317842 |
| Pages | 700 |
| Price | $49.99 |
PHP3 and MySQL Web Development introduces you to the advantages of
implementing both MySQL and PHP3. These advantages are detailed
through the provision of both statistics and several case studies. A
practical web application is developed throughout the book, providing
you with the tools necessary to implement a functional online
database. Each function is developed separately, allowing you the
choice to incorporate only those parts that you would like to
implement. Programming concepts of the PHP3 language are highlighted,
including functions which tie MySQL support into a PHP3 script and
advanced topics regarding table manipulation.
Books recommended by the MySQL Developers
SQL-99 Complete, Really
| Available | Barnes and Noble |
| Publisher | CMP Books |
| Authors | Peter Gulutzan, Trudy Pelzer |
| Pub Date | April 1999 |
| ISBN | 0879305681 |
| Pages | 1104 |
| Price | $55.96 |
This book contains complete descriptions of the new standards for
syntax, data structures, and retrieval processes of SQL databases. As
an example-based reference manual, it includes all of the CLI
functions, information, schema tables, and status codes, as well as a
working SQL database provided on the companion disk.
C, A reference manual
| Available | Barnes and Noble |
| Publisher | Prentice Hall |
| Authors | Samuel P. Harbison, Guy L. Steele |
| Pub Date | September 1994 |
| ISBN | 0133262243 |
| Pages | 480 |
| Price | $35.99 |
A new and improved revision of the bestselling C language
reference. This manual introduces the notion of "Clean C, " writing C
code that can be compiled as a C++ program, C programming style that
emphasizes correctness, portability, and maintainability. and
incorporates the ISO C Amendment 1 (1994) which specifies new
facilities for writing portable, international programs in C.
C++ for Real Programmers
| Available | Barnes and Noble |
| Publisher | Academic Press, Incorporated |
| Authors | Jeff Alger, Jim Keogh |
| Pub Date | February 1998 |
| ISBN | 0120499428 |
| Pages | 388 |
| Price | $39.95 |
C++ For Real Programmers bridges the gap between C++ as described in
beginner and intermediate-level books and C++ as it is practiced by
experts. Numerous valuable techniques are described, organized into
three simple themes: indirection, class hierarchies, and memory
management. It also provides indepth coverage of template creation,
exception handling, pointers and optimization techniques. The focus of
the book is on ANSI C++ and so is compiler independent. C++ For Real
Programmers is a revision of Secrets of the C++ Masters and includes a
new appendix comparing C++ with Java. The book comes with a 3.5" disk
for Windows with source code.
Algorithms in C
| Available | Barnes and Noble |
| Publisher | Addison Wesley Longman, Inc. |
| Authors | Robert Sedgewick |
| Pub Date | April 1990 |
| ISBN | 0201514257 |
| Pages | 648 |
| Price | $45.75 |
Algorithms in C describes a variety of algorithms in a number of areas
of interest, including: sorting, searching, string-processing, and
geometric, graph and mathematical algorithms. The book emphasizes
fundamental techniques, providing readers with the tools to
confidently implement, run, and debug useful algorithms.
Multithreaded Programming with Pthreads
| Available | Barnes and Noble |
| Publisher | Prentice Hall |
| Authors | Bil Lewis, Daniel J. Berg |
| Pub Date | October 1997 |
| ISBN | 0136807291 |
| Pages | 432 |
| Price | $34.95 |
Based on the best-selling Threads Primer, Multithreaded Programming
with Pthreads gives you a solid understanding of Posix threads: what
they are, how they work, when to use them, and how to optimize
them. It retains the clarity and humor of the Primer, but includes
expanded comparisons to Win32 and OS/2 implementations. Code examples
tested on all of the major UNIX platforms are featured along with
detailed explanations of how and why they use threads.
Programming the PERL DBI: Database Programming with PERL
| Available | Barnes and Noble |
| Publisher | O'Reilly & Associates, Incorporated |
| Authors | Alligator Descartes, Tim Bunce |
| Pub Date | February 2000 |
| ISBN | 1565926994 |
| Pages | 400 |
| Price | $27.96 |
Programming the Perl DBI is coauthored by Alligator Descartes, one of the most active members of the DBI community, and by Tim Bunce, the inventor of DBI. For the uninitiated, the book explains the architecture of DBI and shows you how to write DBI-based programs. For the experienced DBI dabbler, this book explains DBI's nuances and the peculiarities of each individual DBD.
The book includes:
The following list describes some of the important characteristics of MySQL:
FLOAT, DOUBLE, CHAR, VARCHAR,
TEXT, BLOB, DATE, TIME, DATETIME,
TIMESTAMP, YEAR, SET, and ENUM types. See section 7.3 Column Types.
SELECT and WHERE
parts of queries. Example:
mysql> SELECT CONCAT(first_name, " ", last_name) FROM tbl_name
WHERE income/dependents > 10000 AND age > 30;
GROUP BY and ORDER BY
clauses. Support for group functions (COUNT(),
COUNT(DISTINCT), AVG(), STD(), SUM(),
MAX() and MIN()).
LEFT OUTER JOIN and RIGHT OUTER JOIN with ANSI
SQL and ODBC syntax.
CHAR or VARCHAR field.
INSERT to insert a
subset of a table's columns; those columns that are not explicitly given
values are set to their default values.
libtool for portability.
purify).
myisamchk, a very fast utility for table checking,
optimization, and repair.
See section 15 Maintaining a MySQL Installation.
DELETE, INSERT, REPLACE, and UPDATE return
how many rows were changed (affected). It is possible to return the number
of rows matched instead by setting a flag when connecting to the server.
ABS
is a valid column name. The only restriction is that for a function call, no
spaces are allowed between the function name and the `(' that follows it.
See section 7.39 Is MySQL Picky About Reserved Words?.
--help or -?
options to obtain online assistance.
SHOW command can be used to retrieve
information about databases, tables, and indexes. The EXPLAIN command
can be used to determine how the optimizer resolves a query.
This section addresses the questions ``How stable is MySQL?'' and ``Can I depend on MySQL in this project?'' We will try to clarify some issues and to answer some of the more important questions that seem to concern many people. This section has been put together from information gathered from the mailing list (which is very active in reporting bugs).
At TcX, MySQL has worked without any problems in our projects since mid-1996. When MySQL was released to a wider public, we noticed that there were some pieces of ``untested code'' that were quickly found by the new users who made queries in a manner different than our own. Each new release has had fewer portability problems than the previous one (even though each has had many new features).
Each release of MySQL has been usable, and there have been problems only when users start to use code from the ``gray zones.'' Naturally, outside users don't know what the gray zones are; this section attempts to indicate those that are currently known. The descriptions deal with Version 3.23.x of MySQL. All known and reported bugs are fixed in the latest version, with the exception of the bugs listed in the bugs section, which are things that are design-related. See section F Known errors and design deficiencies in MySQL.
MySQL is written in multiple layers and different independent modules. These modules are listed below with an indication of how well-tested each of them is:
mysql, mysqladmin, mysqlshow,
mysqldump, and mysqlimport.
fcntl()). In these cases, you should run the
MySQL daemon with the --skip-locking flag. Problems are known
to occur on some Linux systems, and on SunOS when using NFS-mounted file
systems.
fcntl() call, which is
fixed by using the --skip-locking option to
mysqld. Some people have reported lockup problems with Version 0.5.
LinuxThreads will need to be recompiled if you plan to use
1000+ concurrent connections. Although it is possible to run that many
connections with the default LinuxThreads (however, you will never go
above 1021), the default stack spacing of 2 MB makes the application
unstable, and we have been able to reproduce a coredump after creating
1021 idle connections. See Linux Notes for more details.
SELECT statements are usually done in one time frame so there shouldn't
be a mutex locking/thread juggling.
LOAD DATA ..., INSERT ... SELECT -- Stable
ALTER TABLE -- Stable
mysqlaccess -- Stable
GRANT -- Stable
MERGE tables is still not that tested. The
other part of the MERGE code is quite well tested.
MySQL AB provides e-mail support for paying customers, but the MySQL mailing list usually provides answers to common questions. Bugs are usually fixed right away with a patch; for serious bugs, there is almost always a new release.
MySQL itself has no problems with Year 2000 (Y2K) compliance:
2069; all 2-digit years are regarded to be in the range
1970 to 2069, which means that if you store 01 in a
year column, MySQL treats it as 2001.
YEAR column type
can store years 0 and 1901 to 2155 in 1 byte and display
them using 2 or 4 digits.
You may run into problems with applications that use MySQL in a
way that is not Y2K-safe. For example, many old applications store
or manipulate years using 2-digit values (which are ambiguous) rather than
4-digit values. This problem may be compounded by applications that use
values such as 00 or 99 as ``missing'' value indicators.
Unfortunately, these problems may be difficult to fix, because different applications may be written by different programmers, each of whom may use a different set of conventions and date-handling functions.
Here is a simple demonstration illustrating that MySQL doesn't have any problems with dates until the year 2030:
mysql> DROP TABLE IF EXISTS y2k;
mysql> CREATE TABLE y2k (date date, date_time datetime, time_stamp timestamp);
mysql> INSERT INTO y2k VALUES ("1998-12-31","1998-12-31 23:59:59",19981231235959);
mysql> INSERT INTO y2k VALUES ("1999-01-01","1999-01-01 00:00:00",19990101000000);
mysql> INSERT INTO y2k VALUES ("1999-09-09","1999-09-09 23:59:59",19990909235959);
mysql> INSERT INTO y2k VALUES ("2000-01-01","2000-01-01 00:00:00",20000101000000);
mysql> INSERT INTO y2k VALUES ("2000-02-28","2000-02-28 00:00:00",20000228000000);
mysql> INSERT INTO y2k VALUES ("2000-02-29","2000-02-29 00:00:00",20000229000000);
mysql> INSERT INTO y2k VALUES ("2000-03-01","2000-03-01 00:00:00",20000301000000);
mysql> INSERT INTO y2k VALUES ("2000-12-31","2000-12-31 23:59:59",20001231235959);
mysql> INSERT INTO y2k VALUES ("2001-01-01","2001-01-01 00:00:00",20010101000000);
mysql> INSERT INTO y2k VALUES ("2004-12-31","2004-12-31 23:59:59",20041231235959);
mysql> INSERT INTO y2k VALUES ("2005-01-01","2005-01-01 00:00:00",20050101000000);
mysql> INSERT INTO y2k VALUES ("2030-01-01","2030-01-01 00:00:00",20300101000000);
mysql> INSERT INTO y2k VALUES ("2050-01-01","2050-01-01 00:00:00",20500101000000);
mysql> SELECT * FROM y2k;
+------------+---------------------+----------------+
| date | date_time | time_stamp |
+------------+---------------------+----------------+
| 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 |
| 1999-01-01 | 1999-01-01 00:00:00 | 19990101000000 |
| 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 |
| 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 |
| 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 |
| 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 |
| 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 |
| 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 |
| 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 |
| 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 |
| 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 |
| 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 |
| 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 |
+------------+---------------------+----------------+
13 rows in set (0.00 sec)
This shows that the DATE and DATETIME types will not
give any problems with future dates (they handle dates until the year
9999).
The TIMESTAMP type, which is used to store the current time, has a
range up to only 2030-01-01. TIMESTAMP has a range of
1970 to 2030 on 32-bit machines (signed value). On 64-bit
machines it handles times up to 2106 (unsigned value).
Even though MySQL is Y2K-compliant, it is your responsibility to provide unambiguous input. See section 7.3.6.1 Y2K Issues and Date Types for MySQL's rules for dealing with ambiguous date input data (data containing 2-digit year values).
The following book has been recommended by several people on the MySQL mailing list:
Judith S. Bowman, Sandra L. Emerson and Marcy Darnovsky The Practical SQL Handbook: Using Structured Query Language Second Edition Addison-Wesley ISBN 0-201-62623-3 http://www.awl.com
The following book has also received some recommendations by MySQL users:
Martin Gruber Understanding SQL ISBN 0-89588-644-8 Publisher Sybex 510 523 8233 Alameda, CA USA
A SQL tutorial is available on the net at http://www.geocities.com/SiliconValley/Vista/2207/sql1.html.
Apart from the following links, you can find and download a lot of MySQL programs, tools and APIs from the Contrib directory.
1.9.1 Tutorials and Manuals
mSQL.
mSQL Tcl.
DBI/DBD.
DBI/DBD modules homepage.
There are also many Web pages that use MySQL. See section B Some MySQL Users. Send any additions to this list to webmaster@mysql.com. We now require that you show a MySQL logo somewhere if you wish your site to be added. (It is okay to have it on a ``used tools'' page or something similar.)
To subscribe to the main MySQL mailing list, send a message to the electronic mail address mysql-subscribe@lists.mysql.com.
To unsubscribe from the main MySQL mailing list, send a message to the electronic mail address mysql-unsubscribe@lists.mysql.com.
Only the address to which you send your messages is significant. The subject line and the body of the message are ignored.
If your reply address is not valid, you can specify your address explicitly.
Adding a hyphen to the subscribe or unsubscribe command word, followed by
your address with the `@' character in your address replaced by a
`='. For example, to subscribe john@host.domain, send a message
to mysql-subscribe-john=host.domain@lists.mysql.com.
Mail to mysql-subscribe@lists.mysql.com or mysql-unsubscribe@lists.mysql.com is handled automatically by the ezmlm mailing list processor. Information about ezmlm is available at The ezmlm Website.
To post a message to the list itself, send your message to
mysql@lists.mysql.com. However, please do not send mail about
subscribing or unsubscribing to mysql@lists.mysql.com, because any
mail sent to that address is distributed automatically to thousands of other
users.
Your local site may have many subscribers to mysql@lists.mysql.com.
If so, it may have a local mailing list, so that messages sent from
lists.mysql.com to your site are propagated to the local list. In such
cases, please contact your system administrator to be added to or dropped
from the local MySQL list.
The following MySQL mailing lists exist:
announce
mysql
mysql-digest
mysql list in digest form. That means you get all individual
messages, sent as one large mail message once a day.
bugs
mysqlbug script (if you are running on Windows, you should
include a description of the operating system and the MySQL version).
Preferably, you should test the problem using the latest stable or
development version of MySQL before posting!
Anyone should be able to repeat the bug by just using
mysql test < script on the included test case. All bugs posted on
this list will be corrected or documented in the next MySQL release!
If there are only small code changes involved, we will also post a patch that
fixes the problem.
bugs-digest
bugs list in digest form.
developer
developer-digest
internals
internals-digest
java
java-digest
java list.
win32
win32-digest
win32 list.
myodbc
myodbc-digest
myodbc list.
plusplus
plusplus-digest
plusplus list.
msql-mysql-modules
msql-mysql-modules-digest
msql-mysql-modules list.
You subscribe or unsubscribe to all lists in the same way as described
above. In your subscribe or unsubscribe message, just put the appropriate
mailing list name rather than mysql. For example, to subscribe to or
unsubscribe from the myodbc list, send a message to
myodbc-subscribe@lists.mysql.com or
myodbc-unsubscribe@lists.mysql.com.
There is also a german mailing list. You can find information about this at: http://www.4t2.com/mysql.
Before posting a bug report or question, please do the following:
If you can't find an answer in the manual or the archives, check with your local MySQL expert. If you still can't find an answer to your question, go ahead and read the next section about how to send mail to mysql@lists.mysql.com.
Writing a good bug report takes patience, but doing it right the first time saves time for us and for you. A good bug report containing a full test case for the bug will make it very likely that we will fix it in the next release. This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.
We encourage everyone to use the mysqlbug script to generate a bug
report (or a report about any problem), if possible. mysqlbug can be
found in the `scripts' directory in the source distribution, or, for a
binary distribution, in the `bin' directory under your MySQL
installation directory. If you are unable to use mysqlbug, you should
still include all the necessary information listed in this section.
The mysqlbug script helps you generate a report by determining much
of the following information automatically, but if something important is
missing, please include it with your message! Please read this section
carefully and make sure that all the information described here is included
in your report.
If you can make a test case that clearly shows the bug, you should post
it to the bugs@lists.mysql.com list. Note that on this list you
should only post a full, repeatable bug report using the mysqlbug
script. If you are running on Windows, you should include a
description of the operating system and the MySQL version.
Preferably, you should test the problem using the latest stable or development
version of MySQL before posting! Anyone should be able to repeat the
bug by just using ``mysql test < script'' on the included test case or
run the shell or perl script that is included in the bug report. All bugs
posted on this list will be corrected or documented in the next MySQL
release! If there are only small code changes involved to correct this
problem, we will also post a patch that fixes the problem.
Remember that it is possible to respond to a message containing too much information, but not to one containing too little. Often people omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is: if you are in doubt about stating something, state it! It is a thousand times faster and less troublesome to write a couple of lines more in your report than to be forced to ask again and wait for the answer because you didn't include enough information the first time.
The most common errors are that people don't indicate the version number of the MySQL distribution they are using, or don't indicate what platform they have MySQL installed on (including the platform version number). This is highly relevant information, and in 99 cases out of 100 the bug report is useless without it! Very often we get questions like, ``Why doesn't this work for me?'' then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has been fixed already in newer MySQL versions. Sometimes the error is platform dependent; in such cases, it is next to impossible to fix anything without knowing the operating system and the version number of the platform.
Remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is MySQL related. Most compilers are under development all the time and become better version by version. To determine whether or not your problem depends on your compiler, we need to know what compiler is used. Note that every compiling problem should be regarded as a bug report and reported accordingly.
It is most helpful when a good description of the problem is included in the bug report. That is, a good example of all the things you did that led to the problem and the problem itself exactly described. The best reports are those that include a full example showing how to reproduce the bug or problem.
If a program produces an error message, it is very important to include the message in your report! If we try to search for something from the archives using programs, it is better that the error message reported exactly matches the one that the program produces. (Even the case should be observed!) You should never try to remember what the error message was; instead, copy and paste the entire message into your report!
If you have a problem with MyODBC, you should try to genereate a MyODBC trace file. See section 18.6 Reporting Problems with MyODBC.
Please remember that many of the people who will read your report will
do so using an 80-column display. When generating reports or examples
using the mysql command line tool, you should therefore use
the --vertical option (or the \G statement terminator)
for output that would exceed the available width for such a display
(for example, with the EXPLAIN SELECT statement; see the
example below).
Please include the following information in your report:
mysqladmin version. mysqladmin can be
found in the `bin' directory under your MySQL installation
directory.
uname -a.
mysqldump --no-data db_name tbl_name1 tbl_name2 .... This is very easy
to do and is a powerful way to get information about any table in a database
that will help us create a situation matching the one you have.
SELECT statements, you should
always include the output of EXPLAIN SELECT ..., and at least the
number of rows that the SELECT statement produces. The more
information you give about your situation, the more likely it is that someone
can help you! For example, the following is an example of a very good bug
report (it should of course be posted with the mysqlbug script):
Example run using the mysql command line tool (note the use of the
\G statement terminator for statements whose output width would
otherwise exceed that of an 80-column display device):
mysql> SHOW VARIABLES;
mysql> SHOW COLUMNS FROM ...\G
<output from SHOW COLUMNS>
mysql> EXPLAIN SELECT ...\G
<output from EXPLAIN>
mysql> FLUSH STATUS;
mysql> SELECT ...;
<A short version of the output from SELECT,
including the time taken to run the query>
mysql> SHOW STATUS;
<output from SHOW STATUS>
mysqladmin variables extended-status processlist in your mail to
provide some information of how your system is performing!
ftp to
transfer it to ftp://support.mysql.com/pub/mysql/secret/. If the data
are really top secret and you don't want to show them even to us, then go ahead
and provide an example using other names, but please regard this as the last
choice.
mysqld
daemon and that you use to run any MySQL client programs. The
options to programs like mysqld and mysql, and to the
configure script, are often keys to answers and are very relevant!
It is never a bad idea to include them anyway! If you use any modules, such
as Perl or PHP, please include the version number(s) of those as well.
mysqldump and create a `README' file
that describes your problem.
Create a compressed archive of your files using
tar and gzip or zip, and use ftp
to transfer the archive to ftp://support.mysql.com/pub/mysql/secret/.
Then send a short description of the problem to mysql@lists.mysql.com.
mysqlaccess, the output of mysqladmin reload, and all
the error messages you get when trying to connect! When you test your
privileges, you should first run mysqlaccess. After this, execute
mysqladmin reload version and try to connect with the program that
gives you trouble. mysqlaccess can be found in the `bin'
directory under your MySQL installation directory.
parse error, please check your syntax closely! If
you can't find something wrong with it, it's extremely likely that your
current version of MySQL doesn't support the query you are
using. If you are using the current version and the manual at
http://www.mysql.com/documentation/manual.php doesn't cover the
syntax you are using, MySQL doesn't support your query. In this
case, your only options are to implement the syntax yourself or e-mail
mysql-licensing@mysql.com and ask for an offer to implement it!
If the manual covers the syntax you are using, but you have an older version
of MySQL, you should check the MySQL change history to see
when the syntax was implemented. See section E MySQL change history. In this case, you have the
option of upgrading to a newer version of MySQL.
myisamchk or CHECK TABLE/
REPAIR TABLE.
See section 15 Maintaining a MySQL Installation.
mysqld
should NEVER crash a table if nothing killed it in the middle
of an update! If you can find the cause of mysqld dying,
it's much easier for us to provide you with a fix for the problem!
See section 20.1 How to Determine What Is Causing Problems.
If you are a support customer, please cross-post the bug report to mysql-support@mysql.com for higher priority treatment, as well as to the appropriate mailing list to see if someone else has experienced (and perhaps solved) the problem.
For information on reporting bugs in MyODBC, see section 18.3 How to Report Problems with MyODBC.
For solutions to some common problems, see See section 20 Problems and Common Errors.
When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarize the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem!
If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer.
Try to summarize the essential part of the question in your reply; don't feel obliged to quote the entire original message.
Please don't post mail messages from your browser with HTML mode turned on! Many users don't read mail with a browser!
This chapter describes MySQL support and licensing arrangements:
The formal terms of the GPL license can be found at section K GNU General Public License. Basically, our licensing policy and intepretation of the GPL is as follows:
Note that older versions of MySQL are still using a more strict license. See the documentation for that version for more information. If you need a commercial MySQL license, because the GPL license doesn't suit your application, you can buy one at https://order.mysql.com/license.htmy.
For normal internal use, MySQL costs nothing. You do not have to pay us if you do not want to.
A license is required if:
A license is NOT required if:
GNU Library General Public License. The mysql command-line
client includes code from the readline library that is under
the GPL.
For circumstances under which a MySQL license is required, you
need a license per machine that runs the mysqld server. However,
a multiple-CPU machine counts as a single machine, and there is no
restriction on the number of MySQL servers that run on one
machine, or on the number of clients concurrently connected to a server
running on that machine!
If you have any questions as to whether or not a license is required for your particular use of MySQL, please read this again and then contact us. See section 3.4.2 Contact Information.
If you require a MySQL license, the easiest way to pay for it is to use the license form on MySQL's secure server at https://order.mysql.com/license.htmy. Other forms of payment are discussed in section 3.4.1 Payment information.
There are several different copyrights on the MySQL distribution:
mysqlclient library is licensed under the LGPL and
programs in the `client' directory is GPL. Each file has a header
that shows which copyright is used for that file.
getopt) library are covered
by the ``GNU LIBRARY GENERAL PUBLIC LICENSE.'' See section L GNU Library General Public License.
regexp library) are covered
by a Berkeley-style copyright.
readline) library
is covered by the ``GNU GENERAL PUBLIC LICENSE.'' See section K GNU General Public License. This is also available as the file `COPYING' in the
distributions.
One goal is that the SQL client library should be free enough that it is possible to add MySQL support into commercial products without a license. For this reason, we chose the LGPL license for the client code.
This means that you can use MySQL for free with any program that uses any of the free software licenses. MySQL is also free for any end user for his own or company usage.
However, if you use MySQL for something important to you, you may want to help secure its development by purchasing licenses or a support contract. See section 3.5 Types of Commercial Support.
The stable versions of MySQL are still using a more strict license. See the documentation for that version for more information.
This section describes some situations illustrating whether or not you must license the MySQL server. Generally these examples involve providing MySQL as an integral part of a product.
Note that a single MySQL license covers any number of CPUs and
mysqld servers on a machine! There is no artificial limit on the number
of clients that connect to the server in any way.
To determine whether or not you need a MySQL license when selling your application, you should ask whether the proper functioning of your application is dependent on the use of MySQL and whether you include the MySQL server with your product. There are several cases to consider:
mysqld server. For example, if you've
designed your application around MySQL, then you've really made
a commercial product that requires the engine, so you need a license.
Internet Service Providers (ISPs) often host MySQL servers for their customers. With the GPL license this does not require a license.
On the other hand, we do encourage people to use ISPs that have MySQL support, as this will give them the confidence that if they have some problem with their MySQL installation, their ISP will be able to solve the problem for them (in some cases with the help from the MySQL development team).
All ISPs that want to keep themselves up-to-date should subscribe
to our announce mailing list so that they can be aware of fatal issues
that may be relevant for their MySQL installations.
Note that if the ISP doesn't have a license for MySQL, it should give its customers at least read access to the source of the MySQL installation so that its customer can verify that it is patched correctly.
If you use MySQL in conjunction with a Web server on Unix, you don't have to pay for a license.
This is true even if you run a commercial Web server that uses MySQL, because you are not selling an embedded MySQL version yourself. However, in this case we would like you to purchase MySQL support, because MySQL is helping your enterprise.
Our current license prices are shown below. These prices are now under review because of the change to a GPL copyright. New prices and terms will be posted on the MySQL web site http://www.mysql.com/ as soon as they are ready.
All prices are in US Dollars. If you pay by credit card, the currency is EURO (European Union Euro) so the prices will differ slightly.
| Number of licenses | Per copy | Total |
| 1 | US $200 | US $200 |
| 10 pack | US $150 | US $1500 |
| 50 pack | US $120 | US $6000 |
For high volume (OEM) purchases, the following prices apply:
| Number of licenses | Per copy | Minimum | Minimum payment |
| 100-999 | US $40 | 100 | US $4000 |
| 1000-2499 | US $25 | 200 | US $5000 |
| 2500-4999 | US $20 | 400 | US $8000 |
For OEM purchases, you must act as the middle-man for eventual problems or extension requests from your users. We also require that OEM customers have at least an extended e-mail support contract. Note that OEM licenses only apply for products where the user doesn't have direct access to the MySQL server (embedded system). In other words, the MySQL server should only be used with the application that was supplied you.
If you have a low-margin high-volume product, you can always talk to us about other terms (for example, a percent of the sale price). If you do, please be informative about your product, pricing, market, and any other information that may be relevant.
A full-price license is not a support agreement and includes very minimal support. This means that we try to answer any relevant questions. If the answer is in the documentation, we will direct you to the appropriate section. If you have not purchased a license or support, we probably will not answer at all.
If you discover what we consider a real bug, we are likely to fix it in any case. But if you pay for support we will notify you about the fix status instead of just fixing it in a later release.
More comprehensive support is sold separately. Descriptions of what each level of support includes are given in section 3.5 Types of Commercial Support. Costs for the various types of commercial support are shown below. Support level prices are in EURO (European Union Euro). One EURO is about 1.17 USD.
| Type of support | Cost per year |
| Basic e-mail support | EURO 170 |
| Extended e-mail support | EURO 1000 |
| Login support | EURO 2000 |
| Extended login support | EURO 5000 |
You may upgrade from any lower level of support to a higher level of support for the difference in price between the two support levels.
Currently we can take SWIFT payments, checks, or credit cards.
Payment should be made to:
Postgirot Bank AB 105 06 STOCKHOLM, SWEDEN TCX DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN SWIFT address: PGSI SESS Account number: 96 77 06 - 3
Specify: license and/or support and your name and e-mail address.
In Europe and Japan you can use EuroGiro (that should be less expensive) to the same account.
If you want to pay by check, make it payable to ``MySQL Finland AB'' and mail it to the address below:
TCX DataKonsult AB BOX 6434, Torsgatan 21 11382 STOCKHOLM, SWEDEN
If you want to pay by credit card over the Internet, you can use MySQL AB's secure license form.
You can also print a copy of the license form, fill it in, and send it by fax to:
+46-8-729 69 05
If you want us to bill you, you can use the license form and write ``bill
us'' in the comment field. You can also mail a message to
sales@mysql.com (not mysql@lists.mysql.com!)
with your company information and ask us to bill you.
For commercial licensing, please contact the MySQL licensing team. The much preferred method is by e-mail to licensing@mysql.com. Fax is also possible but handling of these may take much longer (Fax +46-8-729 69 05).
If you represent a business that is interested in partnering with MySQL, please send e-mail to partner@mysql.com.
For timely, precise answers to technical questions about MySQL you should order one of our support contracts. MySQL support is provided by the MySQL developers so the standard is extremely high.
If you are interested in placing a banner advertisement on our Web site, please send e-mail to advertising@mysql.com.
If you are interested in any of the jobs listed in our jobs section, please send e-mail to jobs@mysql.com.
For general discussion amongst our many users, please direct your attention to the appropriate mailing list.
For general information inquires, please send e-mail to info@mysql.com.
For questions or comments about the workings or content of this Web site, please send e-mail to webmaster@mysql.com.
Basic e-mail support is a very inexpensive support option and should be thought of more as a way to support our development of MySQL than as a real support option. We at MySQL do give a lot of free support in all the different MySQL lists, and the money we get from basic e-mail support is largely used to make this possible.
At this support level, the MySQL mailing lists are the preferred means of communication. Questions normally should be mailed to the primary mailing list (mysql@lists.mysql.com) or one of the other regular lists (for example, win32@lists.mysql.com for Windows-related MySQL questions), as someone else already may have experienced and solved the problem you have. See section 2.2 Asking Questions or Reporting Bugs.
However, by purchasing basic e-mail support, you also have access to the support address mysql-support@mysql.com, which is not available as part of the minimal support that you get by purchasing a MySQL license. This means that for especially critical questions, you can cross-post your message to mysql-support@mysql.com. (If the message contains sensitive data, you should post only to mysql-support@mysql.com.)
REMEMBER! to ALWAYS include your registration number and expiration date when you send a message to mysql-support@mysql.com.
Note that if you have encountered a critical repeatable bug and follow the rules outlined in the manual section of how to report bugs and send it to bugs@lists.mysql.com, we promise to try to fix this as soon as possible, regardless of your support level! See section 2.3 How to Report Bugs or Problems.
Basic e-mail support includes the following types of service:
Extended e-mail support includes everything in basic e-mail support with these additions:
mysqld for your situation.
Login support includes everything in extended e-mail support with these additions:
kill -9 command).
Extended login support includes everything in login support with these additions:
mysql> select MY_FUNC(col1,col2) from table;
This chapter describes how to obtain and install MySQL:
Check the MySQL home page for information about the current version and for downloading instructions.
Our main download mirror is located at:
http://download.sourceforge.net/mirrors/mysql/
If you are interested in becoming a MySQL mirror site, you may
anonymously rsync with: rsync://download.sourceforge.net/mysql/. Please
send e-mail to webmaster@mysql.com notifying us of your mirror to be
added to the list below.
If you have problems downloading from our main site, try using one of the mirrors listed below.
Please report bad or out-of-date mirrors to webmaster@mysql.com.
Europe:
North America:
South America:
Asia:
Australia:
Africa:
We use GNU Autoconf, so it is possible to port MySQL to all modern systems with working Posix threads and a C++ compiler. (To compile only the client code, a C++ compiler is required but not threads.) We use and develop the software ourselves primarily on Sun Solaris (Versions 2.5 - 2.7) and RedHat Linux Version 6.x.
Note that for many operating systems, the native thread support works only in the latest versions. MySQL has been reported to compile sucessfully on the following operating system/thread package combinations:
glibc 2.0.7+ . See section 4.12.5 Linux Notes (All Linux Versions).
The first decision to make is whether you want to use the latest development release or the last stable release:
crash-me and benchmark tests.
See section 12.7 Using Your Own Benchmarks. Note that all MySQL releases are
checked with the MySQL benchmarks and an extensive test suite
before each release.
The second decision to make is whether you want to use a source distribution or a binary distribution. In most cases you should probably use a binary distribution, if there exist one for your platform, as this is generally, it will be easier to install than a source distribution.
In the following cases you will probably be better of with a source installation:
mysqld with some extra feature that is NOT in
the standard binary distributions. Here is a list of the most common
extra options that you may want to use
The MySQL naming scheme uses release numbers that consist of three
numbers and a suffix. For example, a release name like
mysql-3.21.17-beta is interpreted like this:
3) describes the file format. All
Version 3 releases have the same file format. When a Version 4 appears, every
table will have to be converted to the new format (nice tools for this will
be included, of course.)
21) is the release level. Normally there are two to
choose from. One is the release/stable branch (currently 22) and the
other is the development branch (currently 23) . Normally both are
stable, but the development version may have quirks, missing documentation on
new features, or may fail to compile on some systems.
17) is the version number within the
release level. This is incremented for each new distribution. Usually you
want the latest version for the release level you have choosen.
beta) indicates the stability level of the release.
The possible suffixes are:
alpha indicates that the release contains some large section of
new code that hasn't been 100% tested. Known bugs (usually there are none)
should be documented in the News section. See section E MySQL change history. There are also new
commands and extensions in most alpha releases. Active development that
may involve major code changes can occur on an alpha release, but everything
will be tested before doing a release. There should be no known bugs in any
MySQL release.
beta means that all new code has been tested. No major new
features that could cause corruption on old code are added. There should
be no known bugs. A version changes from alpha to beta when there
haven't been any reported fatal bugs within an alpha version for at least
a month and we don't plan to add any features that could make any old command
more unreliable.
gamma is a beta that has been around a while and seems to work fine.
Only minor fixes are added. This is what many other companies call a release.
All versions of MySQL are run through our standard tests and benchmarks to ensure that they are relatively safe to use. Because the standard tests are extended over time to check for all previously found bugs, the test suite keeps getting better.
Note that all releases have been tested at least with:
crash-me test
Another test is that we use the newest MySQL version in our internal production environment, on at least one machine. We have more than 100 gigabytes of data to work with.
MySQL is evolving quite rapidly here at MySQL AB and we want to share this with other MySQL users. We try to make a release when we have very useful features that others seem to have a need for.
We also try to help out users who request features that are easy to implement. We take note of what our licensed users want to have, and we especially take note of what our extended e-mail supported customers want and try to help them out.
No one has to download a new release. The News section will tell you if the new release has something you really want. See section E MySQL change history.
We use the following policy when updating MySQL:
The current stable release is Version 3.22; We have already moved active development to Version 3.23. Bugs will still be fixed in the stable version. We don't believe in a complete freeze, as this also leaves out bug fixes and things that ``must be done.'' ``Somewhat frozen'' means that we may add small things that ``almost surely will not affect anything that's already working.''
This section describes the default layout of the directories created by installing binary and source distributions.
A binary distribution is installed by unpacking it at the installation location you choose (typically `/usr/local/mysql') and creates the following directories in that location:
| Directory | Contents of directory |
| `bin' | Client programs and the mysqld server
|
| `data' | Log files, databases |
| `include' | Include (header) files |
| `lib' | Libraries |
| `scripts' | mysql_install_db
|
| `share/mysql' | Error message files |
| `sql-bench' | Benchmarks |
A source distribution is installed after you configure and compile it. By default, the installation step installs files under `/usr/local', in the following subdirectories:
| Directory | Contents of directory |
| `bin' | Client programs and scripts |
| `include/mysql' | Include (header) files |
| `info' | Documentation in Info format |
| `lib/mysql' | Libraries |
| `libexec' | The mysqld server
|
| `share/mysql' | Error message files |
| `sql-bench' | Benchmarks and crash-me test
|
| `var' | Databases and log files |
Within an installation directory, the layout of a source installation differs from that of a binary installation in the following ways:
mysqld server is installed in the `libexec'
directory rather than in the `bin' directory.
mysql_install_db is installed in the `/usr/local/bin' directory
rather than in `/usr/local/mysql/scripts'.
You can create your own binary installation from a compiled source distribution by executing the script `scripts/make_binary_distribution'.
You need the following tools to install a MySQL binary distribution:
gunzip to uncompress the distribution.
tar to unpack the distribution. GNU tar is
known to work. Sun tar is known to have problems.
An alternative installation method under Linux is to use RPM (RedHat Package Manager) distributions. See section 4.6.1 Linux RPM Notes.
If you run into problems, PLEASE ALWAYS USE mysqlbug when
posting questions to mysql@lists.mysql.com. Even if the problem
isn't a bug, mysqlbug gathers system information that will help others
solve your problem. By not using mysqlbug, you lessen the likelihood
of getting a solution to your problem! You will find mysqlbug in the
`bin' directory after you unpack the distribution. See section 2.3 How to Report Bugs or Problems.
The basic commands you must execute to install and use a MySQL binary distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> cd /usr/local shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysql shell> cd mysql shell> scripts/mysql_install_db shell> chown -R mysql /usr/local/mysql shell> chgrp -R mysql /usr/local/mysql shell> bin/safe_mysqld --user=mysql &
You can add new users using the bin/mysql_setpermission script if
you install the DBI and Msql-Mysql-modules Perl modules.
A more detailed description follows.
To install a binary distribution, follow the steps below, then proceed to section 4.16 Post-installation Setup and Testing, for post-installation setup and testing:
root.)
tar
archives and have names like `mysql-VERSION-OS.tar.gz', where
VERSION is a number (for example, 3.21.15), and OS
indicates the type of operating system for which the distribution is intended
(for example, pc-linux-gnu-i586).
mysqld to run as:
shell> groupadd mysql shell> useradd -g mysql mysqlThese commands add the
mysql group and the mysql user. The
syntax for useradd and groupadd may differ slightly on different
Unixes. They may also be called adduser and addgroup. You may
wish to call the user and group something else instead of mysql.
shell> cd /usr/local
shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysqlThe first command creates a directory named `mysql-VERSION-OS'. The second command makes a symbolic link to that directory. This lets you refer more easily to the installation directory as `/usr/local/mysql'.
shell> cd mysqlYou will find several files and subdirectories in the
mysql directory.
The most important for installation purposes are the `bin' and
`scripts' subdirectories.
PATH environment variable so that your shell finds the MySQL
programs properly. See section A Environment Variables.
mysql_install_db script used to initialize
the server access permissions.
mysqlaccess and have the MySQL
distribution in some nonstandard place, you must change the location where
mysqlaccess expects to find the mysql client. Edit the
`bin/mysqlaccess' script at approximately line 18. Search for a line
that looks like this:
$MYSQL = '/usr/local/bin/mysql'; # path to mysql executableChange the path to reflect the location where
mysql actually is
stored on your system. If you do not do this, you will get a Broken
pipe error when you run mysqlaccess.
shell> scripts/mysql_install_dbNote that MySQL versions older than Version 3.22.10 started the MySQL server when you run
mysql_install_db. This is no
longer true!
mysqld as:
shell> chown -R mysql /usr/local/mysql shell> chgrp -R mysql /usr/local/mysqlThe first command changes the
owner attribute of the files to the
mysql user, and the second changes the group attribute to
the mysql group.
DBI/DBD interface,
see section 4.11 Perl Installation Comments.
support-files/mysql.server to the location where
your system has its startup files. More information can be found in the
support-files/mysql.server script itself and in section 4.16.3 Starting and Stopping MySQL Automatically.
After everything has been unpacked and installed, you should initialize and test your distribution.
You can start the MySQL server with the following command:
shell> bin/safe_mysqld --user=mysql &
See section 14.2 safe_mysqld, the wrapper around mysqld.
See section 4.16 Post-installation Setup and Testing.
The recommended way to install MySQL on Linux is by using an RPM
file. The MySQL RPMs are currently being built on a RedHat Version
6.2 system but should work on other versions of Linux that support rpm
and use glibc.
If you have problems with an RPM file, for example, if you receive the error
``Sorry, the host 'xxxx' could not be looked up'', see
section 4.6.3.1 Linux Notes for Binary Distributions.
The RPM files you may want to use are:
MySQL-VERSION.i386.rpm
The MySQL server. You will need this unless you only want to
connect to a MySQL server running on another machine.
MySQL-client-VERSION.i386.rpm
The standard MySQL client programs. You probably always want to
install this package.
MySQL-bench-VERSION.i386.rpm
Tests and benchmarks. Requires Perl and msql-mysql-modules RPMs.
MySQL-devel-VERSION.i386.rpm
Libraries and include files needed if you want to compile other
MySQL clients, such as the Perl modules.
MySQL-VERSION.src.rpm
This contains the source code for all of the above packages. It can also
be used to try to build RPMs for other architectures (for example, Alpha
or SPARC).
To see all files in an RPM package, run:
shell> rpm -qpl MySQL-VERSION.i386.rpm
To perform a standard minimal installation, run:
shell> rpm -i MySQL-VERSION.i386.rpm MySQL-client-VERSION.i386.rpm
To install just the client package, run:
shell> rpm -i MySQL-client-VERSION.i386.rpm
The RPM places data in `/var/lib/mysql'. The RPM also creates the appropriate entries in `/etc/rc.d/' to start the server automatically at boot time. (This means that if you have performed a previous installation, you may want to make a copy of your previously installed MySQL startup file if you made any changes to it, so you don't lose your changes.)
After installing the RPM file(s), the `mysqld' daemon should be running and you should now be able to start using MySQL. See section 4.16 Post-installation Setup and Testing.
If something goes wrong, you can find more information in the binary installation chapter. See section 4.6 Installing a MySQL Binary Distribution.
If you compile MySQL clients that you've written yourself or that
you obtain from a third party, they must be linked using the
-lmysqlclient option on the link command. You may also need to
specify a -L option to tell the linker where to find the library. For
example, if the library is installed in `/usr/local/mysql/lib', use
-L/usr/local/mysql/lib -lmysqlclient on the link command.
For clients that use MySQL header files, you may need to specify a
-I option when you compile them (for example,
-I/usr/local/mysql/include), so the compiler can find the header
files.
The following sections indicate some of the issues that have been observed on particular systems when installing MySQL from a binary distribution.
MySQL needs at least Linux Version 2.0.
The binary release is linked with -static, which means you do not
normally need to worry about which version of the system libraries you
have. You need not install LinuxThreads, either. A program linked with
-static is slightly bigger than a dynamically linked program but
also slightly faster (3-5%). One problem, however, is that you can't use
user-definable functions (UDFs) with a statically linked program. If
you are going to write or use UDF functions (this is something only for
C or C++ programmers), you must compile MySQL yourself, using
dynamic linking.
If you are using a libc-based system (instead of a glibc2
system), you will probably get some problems with hostname resolving and
getpwnam() with the binary release. (This is because glibc
unfortunately depends on some external libraries to resolve hostnames
and getpwent() , even when compiled with -static). In this case
you probably get the following error message when you run
mysql_install_db:
Sorry, the host 'xxxx' could not be looked up
or the following error when you try to run mysqld with the --user
option:
getpwnam: No such file or directory
You can solve this problem in one of the following ways:
tar.gz
distribution) and install this instead.
mysql_install_db --force; This will not execute the
resolveip test in mysql_install_db. The downside is that
you can't use host names in the grant tables; you must use IP numbers
instead (except for localhost). If you are using an old MySQL
release that doesn't support --force, you have to remove the
resolveip test in mysql_install with an editor.
su instead of using --user.
The Linux-Intel binary and RPM releases of MySQL are configured for the highest possible speed. We are always trying to use the fastest stable compiler available.
MySQL Perl support requires Version Perl 5.004_03 or newer.
On some Linux 2.2 versions, you may get the error Resource
temporarily unavailable when you do a lot of new connections to a
mysqld server over TCP/IP.
The problem is that Linux has a delay between when you close a TCP/IP socket and until this is actually freed by the system. As there is only room for a finite number of TCP/IP slots, you will get the above error if you try to do too many new TCP/IP connections during a small time, like when you run the MySQL `test-connect' benchmark over TCP/IP.
We have mailed about this problem a couple of times to different Linux mailing lists but have never been able to resolve this properly.
The only known 'fix' to this problem is to use persistent connections in
your clients or use sockets, if you are running the database server
and clients on the same machine. We hope that the Linux 2.4
kernel will fix this problem in the future.
Some of the binary distributions of MySQL for HP-UX is distributed as an HP depot file and as a tar file. To use the depot file you must be running at least HP-UX 10.x to have access to HP's software depot tools.
The HP version of MySQL was compiled on an HP 9000/8xx server under HP-UX 10.20, and uses MIT-pthreads. It is known to work well under this configuration. MySQL Version 3.22.26 and newer can also be built with HP's native thread package.
Other configurations that may work:
The following configurations almost definitely won't work:
To install the distribution, use one of the commands below, where
/path/to/depot is the full pathname of the depot file:
shell> /usr/sbin/swinstall -s /path/to/depot mysql.full
shell> /usr/sbin/swinstall -s /path/to/depot mysql.server
shell> /usr/sbin/swinstall -s /path/to/depot mysql.client
shell> /usr/sbin/swinstall -s /path/to/depot mysql.developer
The depot places binaries and libraries in `/opt/mysql' and data in
`/var/opt/mysql'. The depot also creates the appropriate entries in
`/etc/init.d' and `/etc/rc2.d' to start the server automatically
at boot time. Obviously, this entails being root to install.
To install the HP-UX tar.gz distribution, you must have a copy of GNU
tar.
You need the following tools to build and install MySQL from source:
gunzip to uncompress the distribution.
tar to unpack the distribution. GNU tar is
known to work. Sun tar is known to have problems.
gcc >= 2.8.1, egcs >=
1.0.2, SGI C++, and SunPro C++ are some of the compilers that are known to
work. libg++ is not needed when using gcc. gcc
2.7.x has a bug that makes it impossible to compile some perfectly legal
C++ files, such as `sql/sql_base.cc'. If you only have gcc 2.7.x,
you must upgrade your gcc to be able to compile MySQL.
gcc >= 2.95.2 is recommended when compiling MySQL
Version 3.23.x.
make program. GNU make is always recommended and is
sometimes required. If you have problems, we recommend trying GNU
make 3.75 or newer.
If you run into problems, PLEASE ALWAYS USE mysqlbug when
posting questions to mysql@lists.mysql.com. Even if the problem
isn't a bug, mysqlbug gathers system information that will help others
solve your problem. By not using mysqlbug, you lessen the likelihood
of getting a solution to your problem! You will find mysqlbug in the
`scripts' directory after you unpack the distribution. See section 2.3 How to Report Bugs or Problems.
The basic commands you must execute to install a MySQL source distribution are:
shell> groupadd mysql shell> useradd -g mysql mysql shell> gunzip < mysql-VERSION.tar.gz | tar -xvf - shell> cd mysql-VERSION shell> ./configure --prefix=/usr/local/mysql shell> make shell> make install shell> scripts/mysql_install_db shell> chown -R mysql /usr/local/mysql shell> chgrp -R mysql /usr/local/mysql shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &
If you start from a source RPM, then do the following:
shell> rpm --rebuild MySQL-VERSION.src.rpm
This will make a binary RPM that you can install.
You can add new users using the bin/mysql_setpermission script if
you install the DBI and Msql-Mysql-modules Perl modules.
A more detailed description follows.
To install a source distribution, follow the steps below, then proceed to section 4.16 Post-installation Setup and Testing, for post-installation initialization and testing:
tar
archives and have names like `mysql-VERSION.tar.gz', where
VERSION is a number like 3.23.29-gamma.
mysqld to run as:
shell> groupadd mysql shell> useradd -g mysql mysqlThese commands add the
mysql group, and the mysql user. The
syntax for useradd and groupadd may differ slightly on different
Unixes. They may also be called adduser and addgroup. You may
wish to call the user and group something else instead of mysql.
shell> gunzip < /path/to/mysql-VERSION.tar.gz | tar xvf -This command creates a directory named `mysql-VERSION'.
shell> cd mysql-VERSIONNote that currently you must configure and build MySQL from this top-level directory. You can not build it in a different directory.
shell> ./configure --prefix=/usr/local/mysql shell> makeWhen you run
configure, you might want to specify some options.
Run ./configure --help for a list of options.
section 4.7.3 Typical configure Options, discusses some of the
more useful options.
If configure fails, and you are going to send mail to
mysql@lists.mysql.com to ask for assistance, please include any
lines from `config.log' that you think can help solve the problem. Also
include the last couple of lines of output from configure if
configure aborts. Post the bug report using the mysqlbug
script. See section 2.3 How to Report Bugs or Problems.
If the compile fails, see section 4.9 Problems Compiling?, for help with
a number of common problems.
shell> make installYou might need to run this command as
root.
shell> scripts/mysql_install_dbNote that MySQL versions older than Version 3.22.10 started the MySQL server when you run
mysql_install_db. This is no
longer true!
mysqld as:
shell> chown -R mysql /usr/local/mysql shell> chgrp -R mysql /usr/local/mysqlThe first command changes the
owner attribute of the files to the
mysql user, and the second changes the group attribute to
the mysql group.
DBI/DBD interface,
see section 4.11 Perl Installation Comments.
support-files/mysql.server to the location where
your system has its startup files. More information can be found in the
support-files/mysql.server script itself and in section 4.16.3 Starting and Stopping MySQL Automatically.
After everything has been installed, you should initialize and test your distribution:
shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &
If that command fails immediately with mysqld daemon ended then you can
find some information in the file
`mysql-data-directory/'hostname'.err'. The likely reason is that
you already have another mysqld server running. See section 21.6 Running Multiple MySQL Servers on the Same Machine.
See section 4.16 Post-installation Setup and Testing.
Sometimes patches appear on the mailing list or are placed in the patches area of the MySQL Web site.
To apply a patch from the mailing list, save the message in which the patch appears in a file, change into the top-level directory of your MySQL source tree, and run these commands:
shell> patch -p1 < patch-file-name shell> rm config.cache shell> make clean
Patches from the FTP site are distributed as plain text files or as files
compressed with gzip. Apply a plain patch as shown above for
mailing list patches. To apply a compressed patch, change into the
top-level directory of your MySQL source tree and run these
commands:
shell> gunzip < patch-file-name.gz | patch -p1 shell> rm config.cache shell> make clean
After applying a patch, follow the instructions for a normal source install,
beginning with the ./configure step. After running the make
install step, restart your MySQL server.
You may need to bring down any currently running server before you run
make install. (Use mysqladmin shutdown to do this.) Some
systems do not allow you to install a new version of a program if it replaces
the version that is currently executing.
configure Options
The configure script gives you a great deal of control over how
you configure your MySQL distribution. Typically you do this
using options on the configure command line. You can also affect
configure using certain environment variables. See section A Environment Variables. For a list of options supported by configure, run
this command:
shell> ./configure --help
Some of the more commonly-used configure options are described below:
--without-server option:
shell> ./configure --without-serverIf you don't have a C++ compiler,
mysql will not compile (it is the
one client program that requires C++). In this case,
you can remove the code in configure that tests for the C++ compiler
and then run ./configure with the --without-server option. The
compile step will still try to build mysql, but you can ignore any
warnings about `mysql.cc'. (If make stops, try make -k
to tell it to continue with the rest of the build even if errors occur.)
configure command, something like one
of these:
shell> ./configure --prefix=/usr/local/mysql
shell> ./configure --prefix=/usr/local \
--localstatedir=/usr/local/mysql/data
The first command changes the installation prefix so that everything is
installed under `/usr/local/mysql' rather than the default of
`/usr/local'. The second command preserves the default installation
prefix, but overrides the default location for database directories
(normally `/usr/local/var') and changes it to
/usr/local/mysql/data.
configure command like this:
shell> ./configure --with-unix-socket-path=/usr/local/mysql/tmp/mysql.sockNote that the given file must be an absolute pathname!
configure like this:
shell> ./configure --with-client-ldflags=-all-static \
--with-mysqld-ldflags=-all-static
gcc and don't have libg++ or libstdc++
installed, you can tell configure to use gcc as your C++
compiler:
shell> CC=gcc CXX=gcc ./configureWhen you use
gcc as your C++ compiler, it will not attempt to link in
libg++ or libstdc++.
If the build fails and produces errors about your compiler or linker not
being able to create the shared library `libmysqlclient.so.#' (`#'
is a version number), you can work around this problem by giving the
--disable-shared option to configure. In this case,
configure will not build a shared libmysqlclient.so.# library.
DEFAULT column values for
non-NULL columns (that is, columns that are not allowed to be
NULL). This causes INSERT statements to generate an error
unless you explicitly specify values for all columns that require a
non-NULL value. To suppress use of default values, run
configure like this:
shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure
--with-charset option:
shell> ./configure --with-charset=CHARSET
CHARSET may be one of big5, cp1251, cp1257,
czech, danish, dec8, dos, euc_kr,
gb2312, gbk, german1, hebrew, hp8,
hungarian, koi8_ru, koi8_ukr, latin1,
latin2, sjis, swe7, tis620, ujis,
usa7, or win1251ukr.
See section 10.1.1 The Character Set Used for Data and Sorting.
If you want to convert characters between the server and the client,
you should take a look at the SET OPTION CHARACTER SET command.
See section 7.33 SET Syntax.
Warning: If you change character sets after having created any
tables, you will have to run myisamchk -r -q on every table. Your
indexes may be sorted incorrectly otherwise. (This can happen if you
install MySQL, create some tables, then reconfigure
MySQL to use a different character set and reinstall it.)
--with-debug option:
shell> ./configure --with-debugThis causes a safe memory allocator to be included that can find some errors and that provides output about what is happening. See section H.1 Debugging a MySQL server.
--with-thread-safe-client configure options. This will create a
libmysqlclient_r library with which you should link your threaded
applications. See section 22.4.57 How to Make a Thread-safe Client.
CAUTION: You should only read this section if you are interested in helping us test our new code. If you just want to get MySQL up and running on your system, you should use either source or binary distribution.
Below are the instructions to obtain our most recent development source tree:
bk clone bk://work.mysql.com:7000 mysql - the initial download
may take a while, depending on the speed of your connection.
cd mysql; bk -r edit; aclocal; autoheader; autoconf;
automake; ./configure with your favorite options, and then
make.
You will need GNU autoconf/automake, libtool, and m4 to do this.
We have a
collection of our standard configure scripts in the BUILD/
subdirectory - if you are lazy, you can do
BUILD/compile-pentium-debug . It will actually work on a lot of
non-x86 machines despite its name.
make install. Be careful with this on
a production machine - this may overwrite your live release binary. We
recommend that if you have another installation of MySQL that
you ./configure with different values for prefix,
tcp-port, and unix-socket-path.
make stage and it does not compile,
please report it to bugs@lists.mysql.com. If you have
installed the update version of the required GNU tools, and they crash
trying to process our configuration files, please report it also. However,
if you execute aclocal and get command not found, or a
similar problem, do not report it - make sure all the needed tools are
installed and your PATH variable is set correctly.
bk clone, do bk pull to get the updates.
bk sccstool. If you see some funny diffs or code that you have a
question about, do not hesitate and e-mail
internals@lists.mysql.com. Also if you think you have a
better idea on how to do something, send an email to the same place
with a patch - bk diffs will produce a patch for you after you
have made changes to the source. If you do not have the time to code
your idea, just send a description.
bk helptool.
All MySQL programs compile cleanly for us with no warnings on
Solaris using gcc. On other systems, warnings may occur due to
differences in system include files. See section 4.10 MIT-pthreads Notes, for warnings
that may occur when using MIT-pthreads. For other problems, check the list
below.
The solution to many problems involves reconfiguring. If you do need to reconfigure, take note of the following:
configure is run after it already has been run, it may use
information that was gathered during its previous invocation. This
information is stored in `config.cache'. When configure starts
up, it looks for that file and reads its contents if it exists, on the
assumption that the information is still correct. That assumption is invalid
when you reconfigure.
configure, you must run make again
to recompile. However, you may want to remove old object files from previous
builds first, because they were compiled using different configuration options.
To prevent old configuration information or object files from being used,
run these commands before rerunning configure:
shell> rm config.cache shell> make clean
Alternatively, you can run make distclean.
The list below describes some of the problems compiling MySQL that have been found to occur most often:
Internal compiler error: program cc1plus got fatal signal 11 or Out of virtual memory or Virtual memory exhaustedThe problem is that
gcc requires huge amounts of memory to compile
`sql_yacc.cc' with inline functions. Try running configure with
the --with-low-memory option:
shell> ./configure --with-low-memoryThis option causes
-fno-inline to be added to the compile line if you
are using gcc and -O0 if you are using something else. You
should try the --with-low-memory option even if you have so much
memory and swap space that you think you can't possibly have run out. This
problem has been observed to occur even on systems with generous hardware
configurations, and the --with-low-memory option usually fixes it.
configure picks c++ as the compiler name and
GNU c++ links with -lg++. If you are using gcc,
that behavior can cause problems during configuration such as this:
configure: error: installation or configuration problem: C++ compiler cannot create executables.You might also observe problems during compilation related to
g++, libg++, or libstdc++.
One cause of these problems is that you may not have g++, or you may
have g++ but not libg++, or libstdc++. Take a look at
the `config.log' file. It should contain the exact reason why your c++
compiler didn't work! To work around these problems, you can use gcc
as your C++ compiler. Try setting the environment variable CXX to
"gcc -O3". For example:
shell> CXX="gcc -O3" ./configureThis works because
gcc compiles C++ sources as well as g++
does, but does not link in libg++ or libstdc++ by default.
Another way to fix these problems, of course, is to install g++,
libg++ and libstdc++.
make to GNU make:
making all in mit-pthreads make: Fatal error in reader: Makefile, line 18: Badly formed macro assignment or make: file `Makefile' line 18: Must be a separator (: or pthread.h: No such file or directorySolaris and FreeBSD are known to have troublesome
make programs.
GNU make Version 3.75 is known to work.
CFLAGS and CXXFLAGS environment
variables. You can also specify the compiler names this way using CC
and CXX. For example:
shell> CC=gcc shell> CFLAGS=-O6 shell> CXX=gcc shell> CXXFLAGS=-O6 shell> export CC CFLAGS CXX CXXFLAGSSee section 4.15 MySQL Binaries, for a list of flag definitions that have been found to be useful on various systems.
gcc compiler:
client/libmysql.c:273: parse error before `__attribute__'
gcc 2.8.1 is known to work, but we recommend using gcc 2.95.2 or
egcs 1.0.3a instead.
mysqld,
configure didn't correctly detect the type of the last argument to
accept(), getsockname(), or getpeername():
cxx: Error: mysqld.cc, line 645: In this statement, the referenced
type of the pointer value "&length" is "unsigned long", which
is not compatible with "int".
new_sock = accept(sock, (struct sockaddr *)&cAddr, &length);
To fix this, edit the `config.h' file (which is generated by
configure). Look for these lines:
/* Define as the base type of the last arg to accept */ #define SOCKET_SIZE_TYPE XXXChange
XXX to size_t or int, depending on your
operating system. (Note that you will have to do this each time you run
configure, because configure regenerates `config.h'.)
"sql_yacc.yy", line xxx fatal: default action causes potential...This is a sign that your version of
yacc is deficient.
You probably need to install bison (the GNU version of yacc)
and use that instead.
mysqld or a MySQL client, run
configure with the --with-debug option, then recompile and
link your clients with the new client library.
See section H.2 Debugging a MySQL client.
This section describes some of the issues involved in using MIT-pthreads.
Note that on Linux you should NOT use MIT-pthreads but install LinuxThreads! See section 4.12.5 Linux Notes (All Linux Versions).
If your system does not provide native thread support, you will need to build MySQL using the MIT-pthreads package. This includes older FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. See section 4.2 Operating Systems Supported by MySQL.
configure with the --with-mit-threads option:
shell> ./configure --with-mit-threadsBuilding in a non-source directory is not supported when using MIT-pthreads, because we want to minimize our changes to this code.
--without-server
to build only the client code, clients will not know whether or not
MIT-pthreads is being used and will use Unix socket connections by default.
Because Unix sockets do not work under MIT-pthreads, this means you will need
to use -h or --host when you run client programs.
--use-locking option.
bind() command fails to bind to a socket without
any error message (at least on Solaris). The result is that all connections
to the server fail. For example:
shell> mysqladmin version mysqladmin: connect to server at '' failed; error: 'Can't connect to mysql server on localhost (146)'The solution to this is to kill the
mysqld server and restart it.
This has only happened to us when we have forced the server down and done
a restart immediately.
sleep() system call isn't interruptible with
SIGINT (break). This is only noticeable when you run mysqladmin
--sleep. You must wait for the sleep() call to terminate before the
interrupt is served and the process stops.
ld: warning: symbol `_iob' has differing sizes:
(file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
file /usr/lib/libc.so value=0x140);
/my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
ld: warning: symbol `__iob' has differing sizes:
(file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
file /usr/lib/libc.so value=0x140);
/my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
implicit declaration of function `int strtoll(...)' implicit declaration of function `int strtoul(...)'
readline to work with MIT-pthreads. (This isn't
needed, but may be interesting for someone.)
Perl support for MySQL is provided by means of the
DBI/DBD client interface. See section 22.5 MySQL Perl API. The Perl
DBD/DBI client code requires Perl Version 5.004 or later. The
interface will not work if you have an older version of Perl.
MySQL Perl support also requires that you've installed MySQL client programming support. If you installed MySQL from RPM files, client programs are in the client RPM, but client programming support is in the developer RPM. Make sure you've installed the latter RPM.
As of Version 3.22.8, Perl support is distributed separately from the main MySQL distribution. If you want to install Perl support, the files you will need can be obtained from http://www.mysql.com/Downloads/Contrib/.
The Perl distributions are provided as compressed tar archives and
have names like `MODULE-VERSION.tar.gz', where MODULE is the
module name and VERSION is the version number. You should get the
Data-Dumper, DBI, and Msql-Mysql-modules distributions
and install them in that order. The installation procedure is shown below.
The example shown is for the Data-Dumper module, but the procedure is
the same for all three distributions:
shell> gunzip < Data-Dumper-VERSION.tar.gz | tar xvf -This command creates a directory named `Data-Dumper-VERSION'.
shell> cd Data-Dumper-VERSION
shell> perl Makefile.PL shell> make shell> make test shell> make install
The make test command is important because it verifies that the
module is working. Note that when you run that command during the
Msql-Mysql-modules installation to exercise the interface code, the
MySQL server must be running or the test will fail.
It is a good idea to rebuild and reinstall the Msql-Mysql-modules
distribution whenever you install a new release of MySQL,
particularly if you notice symptoms such as all your DBI scripts
dumping core after you upgrade MySQL.
If you don't have the right to install Perl modules in the system directory or if you to install local Perl modules, the following reference may help you:
http://www.iserver.com/support/contrib/perl5/modules.html
Look under the heading
Installing New Modules that Require Locally Installed Modules.
To install the MySQL DBD module with ActiveState Perl on
Windows, you should do the following:
set HTTP_proxy=my.proxy.com:3128
C:\perl\bin\ppm.pl
DBI: install DBI
ftp://ftp.de.uu.net/pub/CPAN/authors/id/JWIED/DBD-mysql-1.2212.x86.ppd
The above should work at least with ActiveState Perl Version 5.6.
If you can't get the above to work, you should instead install the MyODBC driver and connect to MySQL server through ODBC:
use DBI;
$dbh= DBI->connect("DBI:ODBC:$dsn","$user","$password") ||
die "Got error $DBI::errstr when connecting to $dsn\n";
The MySQL Perl distribution contains DBI,
DBD:MySQL and DBD:ODBC.
C: so that you get a `C:\PERL' directory.
perl works by executing perl -v in a DOS shell.
DBI/DBD Interface
If Perl reports that it can't find the ../mysql/mysql.so module,
then the problem is probably that Perl can't locate the shared library
`libmysqlclient.so'.
You can fix this by any of the following methods:
Msql-Mysql-modules distribution with perl
Makefile.PL -static -config rather than perl Makefile.PL.
libmysqlclient.so to the directory where your other shared
libraries are located (probably `/usr/lib' or `/lib').
Linux you can add the pathname of the directory where
libmysqlclient.so is located to the `/etc/ld.so.conf' file.
libmysqlclient.so is located
to the LD_RUN_PATH environment variable.
If you get the following errors from DBD-mysql,
you are probably using gcc (or using an old binary compiled with
gcc):
/usr/bin/perl: can't resolve symbol '__moddi3' /usr/bin/perl: can't resolve symbol '__divdi3'
Add -L/usr/lib/gcc-lib/... -lgcc to the link command when the
`mysql.so' library gets built (check the output from make for
`mysql.so' when you compile the Perl client). The -L option
should specify the pathname of the directory where `libgcc.a' is located
on your system.
Another cause of this problem may be that Perl and MySQL aren't both
compiled with gcc. In this case, you can solve the mismatch by
compiling both with gcc.
If you get the following error from Msql-Mysql-modules
when you run the tests:
t/00base............install_driver(mysql) failed: Can't load '../blib/arch/auto/DBD/mysql/mysql.so' for module DBD::mysql: ../blib/arch/auto/DBD/mysql/mysql.so: undefined symbol: uncompress at /usr/lib/perl5/5.00503/i586-linux/DynaLoader.pm line 169.
it means that you need to include the compression library, -lz, to the link line. This can be doing the following change in the file `lib/DBD/mysql/Install.pm':
$sysliblist .= " -lm"; to $sysliblist .= " -lm -lz";
After this, you MUST run 'make realclean' and then proceed with the installation from the beginning.
If you want to use the Perl module on a system that doesn't support dynamic
linking (like SCO) you can generate a static version of Perl that includes
DBI and DBD-mysql. The way this works is that you generate a
version of Perl with the DBI code linked in and install it on top of
your current Perl. Then you use that to build a version of Perl that
additionally has the DBD code linked in, and install that.
On SCO, you must have the following environment variables set:
shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib or shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:/usr/skunk/man:
First, create a Perl that includes a statically linked DBI by running
these commands in the directory where your DBI distribution is
located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Then you must install the new Perl. The output of make perl will
indicate the exact make command you will need to execute to perform
the installation. On SCO, this is make -f Makefile.aperl inst_perl
MAP_TARGET=perl.
Next, use the just-created Perl to create another Perl that also includes a
statically-linked DBD::mysql by running these commands in the
directory where your Msql-Mysql-modules distribution is located:
shell> perl Makefile.PL -static -config shell> make shell> make install shell> make perl
Finally, you should install this new Perl. Again, the output of make
perl indicates the command to use.
The following sections indicate some of the issues that have been observed to occur on particular systems when installing MySQL from a source distribution.
On Solaris, you may run into trouble even before you get the MySQL
distribution unpacked! Solaris tar can't handle long file names, so
you may see an error like this when you unpack MySQL:
x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks tar: directory checksum error
In this case, you must use GNU tar (gtar) to unpack the
distribution. You can find a precompiled copy for Solaris at
http://www.mysql.com/Downloads/.
Sun native threads work only on Solaris 2.5 and higher. For Version 2.4 and earlier, MySQL will automatically use MIT-pt threads. See section 4.10 MIT-pthreads Notes.
If you get the following error from configure:
checking for restartable system calls... configure: error can not run test programs while cross compiling
this means that you have something wrong with your compiler installation!
In this case you should upgrade your compiler to a newer version. You may
also be able to solve this problem by inserting the following row into the
config.cache file:
ac_cv_sys_restartable_syscalls=${ac_cv_sys_restartable_syscalls='no'}
If you are using Solaris on a SPARC, the recommended compiler is
gcc 2.95.2. You can find this at http://gcc.gnu.org/.
Note that egs 1.1.1 and gcc 2.8.1 don't work reliably on
SPARC!
The recommended configure line when using gcc 2.95.2 is:
shell> CC=gcc CFLAGS="-O6" \
CXX=gcc CXXFLAGS="-O6 -felide-constructors -fno-exceptions -fno-rtti" \
./configure --prefix=/usr/local/mysql --with-low-memory
If you have the Sun Workshop 4.2 compiler, you can run configure like
this:
shell> CC=cc CFLAGS="-Xa -fast -xO4 -native -xstrconst -mt" \
CXX=CC CXXFLAGS="-noex -XO4 -mt" \
./configure
You may also have to edit the configure script to change this line:
#if !defined(__STDC__) || __STDC__ != 1
to this:
#if !defined(__STDC__)
If you turn on __STDC__ with the -Xc option, the Sun compiler
can't compile with the Solaris `pthread.h' header file. This is a Sun
bug (broken compiler or broken include file).
If mysqld issues the error message shown below when you run it, you have
tried to compile MySQL with the Sun compiler without enabling the
multi-thread option (-mt):
libc internal error: _rmutex_unlock: rmutex not held
Add -mt to CFLAGS and CXXFLAGS and try again.
If you get the following error when compiling MySQL with gcc,
it means that your gcc is not configured for your version of Solaris:
shell> gcc -O3 -g -O2 -DDBUG_OFF -o thr_alarm ... ./thr_alarm.c: In function `signal_hand': ./thr_alarm.c:556: too many arguments to function `sigwait'
The proper thing to do in this case is to get the newest version of
gcc and compile it with your current gcc compiler! At
least for Solaris 2.5, almost all binary versions of gcc have
old, unusable include files that will break all programs that use
threads (and possibly other programs)!
Solaris doesn't provide static versions of all system libraries
(libpthreads and libdl), so you can't compile MySQL
with --static. If you try to do so, you will get the error:
ld: fatal: library -ldl: not found
If too many processes try to connect very rapidly to mysqld, you will
see this error in the MySQL log:
Error in accept: Protocol error
You might try starting the server with the --set-variable back_log=50
option as a workaround for this. See section 4.16.4 Command-line Options.
If you are linking your own MySQL client, you might get the following error when you try to execute it:
ld.so.1: ./my: fatal: libmysqlclient.so.#: open failed: No such file or directory
The problem can be avoided by one of the following methods:
-Lpath):
-Wl,r/full-path-to-libmysqlclient.so.
libmysqclient.so to `/usr/lib'.
libmysqlclient.so is located
to the LD_RUN_PATH environment variable before running your client.
When using the --with-libwrap configure option, you must also
include the libraries that libwrap.a needs:
--with-libwrap="/opt/NUtcpwrapper-7.6/lib/libwrap.a -lnsl -lsocket
If you have problems with configure trying to link with -lz and
you don't have zlib installed, you have two options:
--with-named-z-libs=no.
If you are using gcc and have problems with loading UDF functions
into MySQL, try adding -lgcc to the link line for the
UDF function.
If you would like MySQL to start automatically, you can copy
`support-files/mysql.server' to `/etc/init.d' and create a
symbolic link to it named /etc/rc3.d/S99mysql.server.
You can normally use a Solaris 2.6 binary on Solaris 2.7 and 2.8. Most of the Solaris 2.6 issues also apply for Solaris 2.7 and 2.8.
Note that MySQL Version 3.23.4 and above should be able to autodetect new versions of Solaris and enable workarounds for the following problems!
Solaris 2.7 / 2.8 has some bugs in the include files. You may see the
following error when you use gcc:
/usr/include/widec.h:42: warning: `getwc' redefined /usr/include/wchar.h:326: warning: this is the location of the previous definition
If this occurs, you can do the following to fix the problem:
Copy /usr/include/widec.h to
.../lib/gcc-lib/os/gcc-version/include and change line 41 from:
#if !defined(lint) && !defined(__lint) to #if !defined(lint) && !defined(__lint) && !defined(getwc)
Alternatively, you can edit `/usr/include/widec.h' directly. Either
way, after you make the fix, you should remove `config.cache' and run
configure again!
If you get errors like this when you run make, it's because
configure didn't detect the `curses.h' file (probably
because of the error in /usr/include/widec.h):
In file included from mysql.cc:50: /usr/include/term.h:1060: syntax error before `,' /usr/include/term.h:1081: syntax error before `;'
The solution to this is to do one of the following:
CFLAGS=-DHAVE_CURSES_H CXXFLAGS=-DHAVE_CURSES_H ./configure.
#define HAVE_TERM line from `config.h' file and
run make again.
If you get a problem that your linker can't find -lz when linking
your client program, the problem is probably that your `libz.so' file is
installed in `/usr/local/lib'. You can fix this by one of the
following methods:
LD_LIBRARY_PATH.
libz.so from /lib.
--with-named-z-libs=no option.
If you are using gcc or egcs on Solaris x86 and you
experience problems with core dumps under load, you should use the
following configure command:
shell> CC=gcc CFLAGS="-O6 -fomit-frame-pointer -DHAVE_CURSES_H" \
CXX=gcc \
CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti -DHAVE_CURSES_H" \
./configure --prefix=/usr/local/mysql
This will avoid problems with the libstdc++ library and with C++
exceptions.
If this doesn't help, you should compile a debug version and run
it with a trace file or under gdb. See section H.1 Debugging a MySQL server.
On SunOS 4, MIT-pthreads is needed to compile MySQL, which in turn
means you will need GNU make.
Some SunOS 4 systems have problems with dynamic libraries and
libtool. You can use the following configure line to avoid
this problem:
shell> ./configure --disable-shared --with-mysqld-ldflags=-all-static
When compiling readline, you may get warnings about duplicate defines.
These may be ignored.
When compiling mysqld, there will be some implicit declaration
of function warnings. These may be ignored.
MySQL uses LinuxThreads on Linux. If you are using an old
Linux version that doesn't have glibc2, you must install
LinuxThreads before trying to compile
MySQL. http://www.mysql.com/Downloads/Linux
Note that glibc versions before and including Version 2.1.1 have a fatal
bug in pthread_mutex_timedwait handling, which is used when you
do INSERT DELAYED. If you are using INSERT DELAYED, you
MUST add the following patch to your glibc library:
http://www.mysql.com/Downloads/Patches/glibc-pthread_cond_timedwait.patch.
MySQL Versions 3.23.7 and 3.22.32 contain a temporary
workaround for this bug.
If you plan to have 1000+ concurrent connections, you will need to make
some changes to LinuxThreads, recompile it, and relink MySQL against
the new `libpthread.a'. Increase PTHREAD_THREADS_MAX in
`sysdeps/unix/sysv/linux/bits/local_lim.h' to 4096 and decrease
STACK_SIZE in `internals.h' to 256 KB. Note that MySQL
will not be stable with around 1000 connections if STACK_SIZE
is the default of 2 MB.
If you have glibc 2.1.3-65 or newer, you don't have to increase STACK_SIZE;
You can instead just change the thread_stack value for mysqld.
If you use a lot of concurrent connections, you may suffer from a Version 2.2 kernel "feature" that penalizes a process for forking or cloning a child in an attempt to prevent a fork bomb attack. This will cause MySQL not to scale well as you increase the number of concurrent clients. On single CPU systems, we have seen this manifested in a very slow thread creation - which means it may take a long time to connect to MySQL (as long as 1 minute), and it may take just as long to shut it down. On multiple CPU systems, we have observed a gradual drop in query speed as the number of clients increases. In the process of trying to find a solution, we have received a kernel patch from one of our users, who claimed it made a lot of difference for his site. We have done some limited testing in which the patch greatly improved the scalabitility of MySQL. The patch is available here (http://www.mysql.com/Downloads/Patches/linux-fork.patch). Be warned, though, that we assume no reponsibility for any damage that this patch could do. Use it at your own risk. We have also been told by the Linux kernel developers that this problem is fixed in Version 2.4, although we have not yet done any testing.
We have also tested MySQL on Linux Version 2.4 on a 2 CPU machine and
MySQL scales MUCH better on this! If your plan to set up a
dedicated Linux SMP machine to run MySQL under heavy load, we
recommend that you give Version 2.4 a try!
The current implementation of mutex in Linuxthreads is also very bad for programs with many threads that only hold the mutex for a short time. We have made a patch available for glibc 2.1, linuxthreads-2.1-patch and for glibc 2.2, linuxthreads-2.2-patch.
If you apply the patches, you are doing this at your own risk. We can only say that they appear to work well for us!.
If you can't start mysqld or if mysql_install_db doesn't work,
please continue reading! This only happens on Linux system with problems in
the LinuxThreads or libc/glibc libraries. There are a lot of
simple workarounds to get MySQL to work! The simplest is to use the
binary version of MySQL (not the RPM) for Linux x86. One nice
aspect of this version is that it's probably 10% faster than any version you
would compile yourself! See section 12.2.1 How Compiling and Linking Affects the Speed of MySQL.
One known problem with the binary distribution is that with older Linux
systems that use libc (like RedHat 4.x or Slackware), you will get
some non-fatal problems with hostname resolution.
See section 4.6.3.1 Linux Notes for Binary Distributions.
myisamchk hangs with libc.so.5.3.12. Upgrading to the newest
libc fixes this problem.
When using LinuxThreads you will see a minimum of three processes running. These are in fact threads. There will be one thread for the LinuxThreads manager, one thread to handle connections, and one thread to handle alarms and signals.
Note that the linux kernel and the linuxthread library can by default only have 1024 threads. This means that you can only have up to 1021 connections to MySQL on a unpatched system. The page http://www.volano.com/linuxnotes.html contains information how to go around this limit.
If you see a dead mysqld daemon process with ps, this usually
means that you have found a bug in MySQL or you have a corrupted
table. See section 20.2 What to Do if MySQL Keeps Crashing.
To get a core dump on Linux if mysqld dies with a SIGSEGV
signal, you can start mysqld with the --core-file option. Note
that you also probably need to raise the core file size by adding
ulimit -c 1000000 to safe_mysqld. See section 14.2 safe_mysqld, the wrapper around mysqld.
If you are using LinuxThreads and mysqladmin shutdown doesn't work,
you must upgrade to LinuxThreads Version 0.7.1 or newer.
If you are using RedHat, you might get errors like this:
/usr/bin/perl is needed... /usr/sh is needed... /usr/sh is needed...
If so, you should upgrade your version of rpm to
`rpm-2.4.11-1.i386.rpm' and `rpm-devel-2.4.11-1.i386.rpm' (or later).
You can get the upgrades of libraries to RedHat Version 4.2 from ftp://ftp.redhat.com/updates/4.2/i386. Or http://www.sunsite.unc.edu/pub/Linux/distributions/redhat/code/rpm/ for other distributions.
If you are linking your own MySQL client and get the error:
ld.so.1: ./my: fatal: libmysqlclient.so.4: open failed: No such file or directory
When executing them, the problem can be avoided by one of the following methods:
-Lpath):
-Wl,r/path-libmysqlclient.so.
libmysqclient.so to `/usr/lib'.
libmysqlclient.so is located
to the LD_RUN_PATH environment variable before running your client.
If you are using the Fujitsu compiler (fcc / FCC) you will have
some problems compiling MySQL because the Linux header files are very
gcc oriented.
The following configure line should work with fcc/FCC:
CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE -DCONST=const -DNO_STRTOLL_PROTO" CXX=FCC CXXFLAGS="-O -K fast -K lib -K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE -DCONST=const -Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO '-D_EXTERN_INLINE=static __inline'" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-low-memory
MySQL requires libc Version 5.4.12 or newer. It's known to
work with libc 5.4.46. glibc Version 2.0.6 and later should
also work. There have been some problems with the glibc RPMs from
RedHat, so if you have problems, check whether or not there are any updates!
The glibc 2.0.7-19 and 2.0.7-29 RPMs are known to work.
On some older Linux distributions, configure may produce an error
like this:
Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file. See the Installation chapter in the Reference Manual.
Just do what the error message says and add an extra underscore to the
_P macro that has only one underscore, then try again.
You may get some warnings when compiling; those shown below can be ignored:
mysqld.cc -o objs-thread/mysqld.o mysqld.cc: In function `void init_signals()': mysqld.cc:315: warning: assignment of negative value `-1' to `long unsigned int' mysqld.cc: In function `void * signal_hand(void *)': mysqld.cc:346: warning: assignment of negative value `-1' to `long unsigned int'
In Debian GNU/Linux, if you want MySQL to start automatically when the system boots, do the following:
shell> cp support-files/mysql.server /etc/init.d/mysql.server shell> /usr/sbin/update-rc.d mysql.server defaults 99
mysql.server can be found in the `share/mysql' directory
under the MySQL installation directory or in the
`support-files' directory of the MySQL source tree.
If mysqld always core dumps when it starts up, the problem may be that
you have an old `/lib/libc.a'. Try renaming it, then remove
`sql/mysqld' and do a new make install and try again. This
problem has been reported on some Slackware installations. RedHat Version 5.0
also has a similar problem with some new glibc versions.
See section 4.12.5.2 RedHat Version 5.0 Notes.
If you get the following error when linking mysqld,
it means that your `libg++.a' is not installed correctly:
/usr/lib/libc.a(putc.o): In function `_IO_putc': putc.o(.text+0x0): multiple definition of `_IO_putc'
You can avoid using `libg++.a' by running configure like this:
shell> CXX=gcc ./configure
If you have any problems with MySQL on RedHat, you should start by
upgrading glibc to the newest possible version!
If you install all the official RedHat patches (including
glibc-2.0.7-19 and glibc-devel-2.0.7-19), both the
binary and source distributions of MySQL should work without
any trouble!
The updates are needed because there is a bug in glibc 2.0.5 in how
pthread_key_create variables are freed. With glibc 2.0.5, you
must use a statically linked MySQL binary distribution. If you
want to compile from source, you must install the corrected version of
LinuxThreads from http://www.mysql.com/Downloads/Linux or upgrade your
glibc.
If you have an incorrect version of glibc or LinuxThreads, the symptom
is that mysqld crashes after each connection. For example,
mysqladmin version will crash mysqld when it finishes!
Another symptom of incorrect libraries is that mysqld crashes at
once when it starts. On some Linux systems, this can be fixed by configuring
like this:
shell> ./configure --with-mysqld-ldflags=-all-static
On Redhat Version 5.0, the easy way out is to install the glibc
2.0.7-19 RPM and run configure without the
--with-mysqld-ldflags=-all-static option.
For the source distribution of glibc 2.0.7, a patch that is easy to
apply and is tested with MySQL may be found at:
http://www.mysql.com/Download/Linux/glibc-2.0.7-total-patch.tar.gz
If you experience crashes like these when you build MySQL, you can always download the newest binary version of MySQL. This is statically-linked to avoid library conflicts and should work on all Linux systems!
MySQL comes with an internal debugger that can generate trace files with a lot of information that can be used to find and solve a wide range of different problems. See section H.1 Debugging a MySQL server.
The glibc of RedHat Version 5.1 (glibc 2.0.7-13) has a memory
leak, so to get a stable MySQL version, you must upgrade glibc,
to 2.0.7-19, downgrade glibc or use a binary version of mysqld.
If you don't do this, you will encounter memory problems (out of memory, etc.).
The most common error in this case is:
Can't create a new thread (errno 11). If you are not out of available memory, you can consult the manual for any possible OS dependent bug
After you have upgraded to glibc 2.0.7-19, you can configure
MySQL with dynamic linking (the default), but you cannot
run configure with the --with-mysqld-ldflags=-all-static option
until you have installed glibc 2.0.7-19 from source!
You can check which version of glibc you have with rpm -q glibc.
Another reason for the above error is if you try to use more threads than your Linux kernel is configured for. In this case you should raise the limits in `include/linux/tasks.h' and recompile your kernel!
In some implementations, readdir_r() is broken. The symptom is that
SHOW DATABASES always returns an empty set. This
can be fixed by removing HAVE_READDIR_R from `config.h' after
configuring and before compiling.
Some problems will require patching your Linux installation. The patch can
be found at
http://www.mysql.com/Downloads/patches/Linux-sparc-2.0.30.diff. This patch is
against the Linux distribution `sparclinux-2.0.30.tar.gz' that is
available at vger.rutgers.edu (a version of Linux that was
never merged with the official 2.0.30). You must also install
LinuxThreads Version 0.6 or newer.
MySQL Version 3.23.12 is the first MySQL version that is tested on Linux-Alpha. If you plan to use MySQL on Linux-Alpha, you should ensure that you have this version or newer.
We have tested MySQL on Alpha with our benchmarks + test suite and it appears to work nicely. The main thing we haven't yet had time to test is how things works with many concurrent users.
When we compiled the standard MySQL binary we are using SuSE 6.4, kernel 2.2.13-SMP, Compaq C compiler (V6.2-504) and Compaq C++ compiler (V6.3-005) on a Comaq DS20 machine with an Alpha EV6 processor
You can find the above compilers at http://www.support.compaq.com/alpha-tools). By using these compilers, instead of gcc, we get about 9-14 % better performance with MySQL.
Note that the configure line optimized the binary for the current CPU; This means you can only use our binary if you have an Alpha EV6 processor. We also compile staticly to avoid library problems.
CC=ccc CFLAGS="-fast" CXX=cxx CXXFLAGS="-fast -noexceptions -nortti" ./configure --prefix=/usr/local/mysql --disable-shared --with-extra-charsets=complex --enable-thread-safe-client --with-mysqld-ldflags=-non_shared --with-client-ldflags=-non_shared
If you want to use egcs the following configure line worked for us:
CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --disable-shared
Some known problems when running MySQL on Linux-Alpha:
gdb 4.18. You should download and use gdb 5.0 instead!
--with-mysqld-ldflags=-all-static with gcc
MySQL should work on MkLinux with the newest glibc package
(tested with glibc 2.0.7).
To get MySQL to work on Qube2, (Linux Mips), you need the
newest glibc libraries (glibc-2.0.7-29C2 is known to
work). You must also use the egcs C++ compiler
(egcs-1.0.2-9, gcc 2.95.2 or newer).
To get MySQL to compile on Linux Ia64, we had to do the following (we assume that this will be easier when next gcc version for ia64 is released).
Using gcc-2.9-final:
CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-extra-charsets=complex
After make you will get an error that sql/opt_range.cc
will not compile (internal compiler error). To fix this, go to the sql
directory and type make again. Copy the compile line, but change
-O2 to -O0. The file should now compile.
Now you can do:
cd .. make make_install
and mysqld should be ready to run.
If you are using egcs 1.1.2 on Digital Unix, you should upgrade to gcc 2.95.2, as egcs on DEC has some serious bugs!
When compiling threaded programs under Digital Unix, the documentation
recommends using the -pthread option for cc and cxx and
the libraries -lmach -lexc (in addition to -lpthread). You
should run configure something like this:
shell> CC="cc -pthread" CXX="cxx -pthread -O" \
./configure --with-named-thread-libs="-lpthread -lmach -lexc -lc"
When compiling mysqld, you may see a couple of warnings like this:
mysqld.cc: In function void handle_connections()': mysqld.cc:626: passing long unsigned int *' as argument 3 of accept(int,sockadddr *, int *)'
You can safely ignore these warnings. They occur because configure
can detect only errors, not warnings.
If you start the server directly from the command line, you may have problems
with it dying when you log out. (When you log out, your outstanding processes
receive a SIGHUP signal.) If so, try starting the server like this:
shell> nohup mysqld [options] &
nohup causes the command following it to ignore any SIGHUP
signal sent from the terminal. Alternatively, start the server by running
safe_mysqld, which invokes mysqld using nohup for you.
See section 14.2 safe_mysqld, the wrapper around mysqld.
If you get a problem when compiling mysys/get_opt.c, just remove the line #define _NO_PROTO from the start of that file!
If you are using Compac's CC compiler, the following configure line should work:
CC="cc -pthread" CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host" CXX="cxx -pthread" CXXFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host" export CC CFLAGS CXX CXXFLAGS ./configure \ --prefix=/usr/local/mysql \ --with-low-memory \ --enable-large-files \ --enable-shared=yes \ --with-named-thread-libs="-lpthread -lmach -lexc -lc" gnumake
If you get a problem with libtool, when compiling with shared libraries
as above, when linking mysql, you should be able to get around
this by issuing:
cd mysql /bin/sh ../libtool --mode=link cxx -pthread -O3 -DDBUG_OFF \ -O4 -ansi_alias -ansi_args -fast -inline speed \ -speculate all \ -arch host -DUNDEF_HAVE_GETHOSTBYNAME_R \ -o mysql mysql.o readline.o sql_string.o completion_hash.o \ ../readline/libreadline.a -lcurses \ ../libmysql/.libs/libmysqlclient.so -lm cd .. gnumake gnumake install scripts/mysql_install_db
If you have problems compiling and have DEC CC and gcc
installed, try running configure like this:
shell> CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \
./configure --prefix=/usr/local/mysql
If you get problems with the `c_asm.h' file, you can create and use a 'dummy' `c_asm.h' file with:
shell> touch include/c_asm.h
shell> CC=gcc CFLAGS=-I./include \
CXX=gcc CXXFLAGS=-O3 \
./configure --prefix=/usr/local/mysql
Note that the following problems with the ld program can be fixed
by downloading the latest DEC (Compaq) patch kit from:
http://ftp.support.compaq.com/public/unix/.
On OSF1 V4.0D and compiler "DEC C V5.6-071 on Digital Unix V4.0 (Rev. 878)"
the compiler had some strange behavior (undefined asm symbols).
/bin/ld also appears to be broken (problems with _exit
undefined errors occuring while linking mysqld). On this system, we
have managed to compile MySQL with the following configure
line, after replacing /bin/ld with the version from OSF 4.0C:
shell> CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
With the Digital compiler "C++ V6.1-029", the following should work:
CC=cc -pthread CFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host CXX=cxx -pthread CXXFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all -arch host export CC CFLAGS CXX CXXFLAGS ./configure --prefix=/usr/mysql/mysql --with-low-memory --enable-large-files --with-mysqld-ldflags=-all-static --disable-shared --with-named-thread-libs="-lmach -lexc -lc"
In some versions of OSF1, the alloca() function is broken. Fix
this by removing the line in `config.h' that defines 'HAVE_ALLOCA'.
The alloca() function also may have an incorrect prototype in
/usr/include/alloca.h. This warning resulting from this can be ignored.
configure will use the following thread libraries automatically:
--with-named-thread-libs="-lpthread -lmach -lexc -lc".
When using gcc, you can also try running configure like this:
shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure ....
If you have problems with signals (MySQL dies unexpectedly under high load), you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM \
CXXFLAGS=-DDONT_USE_THR_ALARM \
./configure ...
This doesn't affect the performance of MySQL, but has the side
effect that you can't kill clients that are ``sleeping'' on a connection with
mysqladmin kill or mysqladmin shutdown. Instead, the client
will die when it issues its next command.
With gcc 2.95.2, you will probably run into the following compile error:
sql_acl.cc:1456: Internal compiler error in `scan_region', at except.c:2566 Please submit a full bug report.
To fix this you should change to the sql directory and do a ``cut
and paste'' of the last gcc line, but change -O3 to
-O0 (or add -O0 immediately after gcc if you don't
have any -O option on your compile line.) After this is done you
can just change back to the top-level directly and run make
again.
If you are using Irix Version 6.5.3 or newer mysqld will only be able to
create threads if you run it as a user with CAP_SCHED_MGT
privileges (like root) or give the mysqld server this privilege
with the following shell command:
shell> chcap "CAP_SCHED_MGT+epi" /opt/mysql/libexec/mysqld
You may have to undefine some things in `config.h' after running
configure and before compiling.
In some Irix implementations, the alloca() function is broken. If the
mysqld server dies on some SELECT statements, remove the lines
from `config.h' that define HAVE_ALLOC and HAVE_ALLOCA_H.
If mysqladmin create doesn't work, remove the line from
`config.h' that defines HAVE_READDIR_R. You may have to remove
the HAVE_TERM_H line as well.
SGI recommends that you install all of the patches on this page as a set: http://support.sgi.com/surfzone/patches/patchset/6.2_indigo.rps.html
At the very minimum, you should install the latest kernel rollup, the
latest rld rollup, and the latest libc rollup.
You definately need all the POSIX patches on this page, for pthreads support:
http://support.sgi.com/surfzone/patches/patchset/6.2_posix.rps.html
If you get the something like the following error when compiling `mysql.cc':
"/usr/include/curses.h", line 82: error(1084): invalid combination of type
then type the following in the top-level directory of your MySQL source tree:
shell> extra/replace bool curses_bool < /usr/include/curses.h > include/curses.h shell> make
There have also been reports of scheduling problems. If only one thread is running, things go slow. Avoid this by starting another client. This may lead to a 2-to-10-fold increase in execution speed thereafter for the other thread. This is a poorly understood problem with Irix threads; you may have to improvise to find solutions until this can be fixed.
If you are compiling with gcc, you can use the following
configure command:
shell> CC=gcc CXX=gcc CXXFLAGS=-O3 \
./configure --prefix=/usr/local/mysql --with-thread-safe-client --with-named-thread-libs=-lpthread
FreeBSD 3.x is recommended for running MySQL since the thread package is much more integrated.
The easiest and therefor the preferred way to install is to use the mysql-server and mysql-client ports available on http://www.freebsd.org.
Using these gives you:
It is recomended you use MIT-pthreads on FreeBSD 2.x and native threads on Versions 3 and up. It is possible to run with native threads on some late 2.2.x versions but you may encounter problems shutting down mysqld.
The MYSQL Makefiles require GNU make (gmake) to work.
If you want to compile MYSQL you need to install GNU make
first.
Be sure to have your name resolver setup correct. Otherwise you may experience resolver delays or failures when connecting to mysqld.
Make sure that the localhost entry in the `/etc/hosts' file is
correct (otherwise you will have problems connecting to the database). The
`/etc/hosts' file should start with a line:
127.0.0.1 localhost localhost.your.domain
If you notice that configure will use MIT-pthreads, you should read
the MIT-pthreads notes. See section 4.10 MIT-pthreads Notes.
If you get an error from make install that it can't find
`/usr/include/pthreads', configure didn't detect that you need
MIT-pthreads. This is fixed by executing these commands:
shell> rm config.cache shell> ./configure --with-mit-threads
FreeBSD is also known to have a very low default file handle limit. See section 20.13 File Not Found. Uncomment the ulimit -n section in safe_mysqld or raise the limits for the mysqld user in /etc/login.conf (and rebuild it witg cap_mkdb /etc/login.conf.) Also be sure you set the appropriate class for this user in the password file if you are not using the default (use: chpass mysqld-user-name). See section 14.2 safe_mysqld, the wrapper around mysqld.
If you get problems with the current date in MySQL, setting the
TZ variable will probably help. See section A Environment Variables.
To get a secure and stable system you should only use FreeBSD kernels
that are marked -STABLE
To compile on NetBSD you need GNU make. Otherwise the compile will crash
when make tries to run lint on C++ files.
On OpenBSD Version 2.5, you can compile MySQL with native threads with the following options:
CFLAGS=-pthread CXXFLAGS=-pthread ./configure --with-mit-threads=no
If you get the following error when compiling MySQL, your
ulimit value for virtual memory is too low:
item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)': item_func.h:28: virtual memory exhausted make[2]: *** [item_func.o] Error 1
Try using ulimit -v 80000 and run make again. If this
doesn't work and you are using bash, try switching to csh
or sh; some BSDI users have reported problems with bash
and ulimit.
If you are using gcc, you may also use have to use the
--with-low-memory flag for configure to be able to compile
`sql_yacc.cc'.
If you get problems with the current date in MySQL, setting the
TZ variable will probably help. See section A Environment Variables.
Upgrade to BSD/OS Version 3.1. If that is not possible, install BSDIpatch M300-038.
Use the following command when configuring MySQL:
shell> env CXX=shlicc++ CC=shlicc2 \
./configure \
--prefix=/usr/local/mysql \
--localstatedir=/var/mysql \
--without-perl \
--with-unix-socket-path=/var/mysql/mysql.sock
The following is also known to work:
shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \
./configure \
--prefix=/usr/local/mysql \
--with-unix-socket-path=/var/mysql/mysql.sock
You can change the directory locations if you wish, or just use the defaults by not specifying any locations.
If you have problems with performance under heavy load, try using the
--skip-thread-priority option to mysqld! This will run
all threads with the same priority; on BSDI Version 3.1, this gives better
performance (at least until BSDI fixes their thread scheduler).
If you get the error virtual memory exhausted while compiling,
you should try using ulimit -v 80000 and run make again.
If this doesn't work and you are using bash, try switching to
csh or sh; some BSDI users have reported problems with
bash and ulimit.
BSDI Version 4.x has some thread-related bugs. If you want to use MySQL on this, you should install all thread-related patches. At least M400-023 should be installed.
On some BSDI Version 4.x systems, you may get problems with shared libraries.
The symptom is that you can't execute any client programs, for example,
mysqladmin. In this case you need to reconfigure not to use
shared libraries with the --disable-shared option to configure.
The current port is tested only on a ``sco3.2v5.0.4'' and ``sco3.2v5.0.5'' system. There has also been a lot of progress on a port to ``sco 3.2v4.2''.
For the moment the recommended compiler on OpenServer is gcc 2.95.2. With this you should be able to compile MySQL with just:
CC=gcc CXX=gcc ./configure ... (options)
gcc 2.7.2 in Skunkware 97 does not have
GNU as. You can also use egcs 1.1.2 or newer
http://www.egcs.com/. If you are using egcs 1.1.2 you have
to execute the following command:
shell> cp -p /usr/include/pthread/stdtypes.h /usr/local/lib/gcc-lib/i386-pc-sco3.2v5.0.5/egcs-2.91.66/include/pthread/
./configure in the `threads/src' directory and select
the SCO OpenServer option. This command copies `Makefile.SCO5' to
`Makefile'.
make.
cd to the `thread/src' directory, and run make
install.
make when making MySQL.
safe_mysqld as root, you probably will get only the
default 110 open files per process. mysqld will write a note about this
in the log file.
configure command should work:
shell> ./configure --prefix=/usr/local/mysql --disable-shared
configure command should work:
shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \
./configure \
--with-debug --prefix=/usr/local/mysql \
--with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \
--with-named-curses-libs="-lcurses"
You may get some problems with some include files. In this case, you can
find new SCO-specific include files at
http://www.mysql.com/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz.
You should unpack this file in the `include'
directory of your MySQL source tree.
SCO development notes:
mysqld
with -lgthreads -lsocket -lgthreads.
malloc. If you encounter problems with memory usage, make sure that
`gmalloc.o'
is included in `libgthreads.a' and `libgthreads.so'.
read(),
write(), getmsg(), connect(), accept(),
select(), and wait().
If you want to install DBI on SCO, you have to edit the `Makefile' in DBI-xxx and each subdirectory.
Note that the following assumes gcc 2.95.2 or newer:
OLD: NEW: CC = cc CC = gcc CCCDLFLAGS = -KPIC -W1,-Bexport CCCDLFLAGS = -fpic CCDLFLAGS = -wl,-Bexport CCDLFLAGS = LD = ld LD = gcc -G -fpic LDDLFLAGS = -G -L/usr/local/lib LDDLFLAGS = -L/usr/local/lib LDFLAGS = -belf -L/usr/local/lib LDFLAGS = -L/usr/local/lib LD = ld LD = gcc -G -fpic OPTIMISE = -Od OPTIMISE = -O1 OLD: CCCFLAGS = -belf -dy -w0 -U M_XENIX -DPERL_SCO5 -I/usr/local/include NEW: CCFLAGS = -U M_XENIX -DPERL_SCO5 -I/usr/local/include
This is because the Perl dynaloader will not load the DBI modules
if they were compiled with icc or cc.
Perl works best when compiled with cc.
You must use a version of MySQL at least as recent as Version 3.22.13 because that version fixes some portability problems under Unixware.
We have been able to compile MySQL with the following configure
command on Unixware Version 7.0.1:
shell> CC=cc CXX=CC ./configure --prefix=/usr/local/mysql
If you want to use gcc, you must use gcc 2.95.2 or newer.
Automatic detection of xlC is missing from Autoconf, so a
configure command something like this is needed when compiling
MySQL (The example uses the IBM compiler):
export CC="xlc_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192 " export CXX="xlC_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192" export CFLAGS="-I /usr/local/include" export LDLFAGS="-L /usr/local/lib" export CPPFLAGS=$CFLAGS export CXXFLAGS=$CFLAGS ./configure --prefix=/usr/local \ --localstatedir=/var/mysql \ --sysconfdir=/etc/mysql \ --sbindir='/usr/local/bin' \ --libexecdir='/usr/local/bin' \ --enable-thread-safe-client \ --enable-large-files
Above are the options used to compile the MySQL distribution that can be found at www-frec.bull.com.
If you change the -O3 to -O2 in the above configure line,
you must also remove the -qstrict option (this is a limitation in
the IBM C compiler).
If you are using gcc or egcs to compile MySQL, you
MUST use the -fno-exceptions flag, as the exception
handling in gcc/egcs is not thread safe! (This is tested with
egcs 1.1.). There are also some known problems with IBM's assembler,
which may cause it to generate bad code when used with gcc.
We recommend the following configure line with egcs and
gcc 2.95 on AIX:
shell> CC="gcc -pipe -mcpu=power2 -Wa,-many" \
CXX="gcc -pipe -mcpu=power2 -Wa,-many" \
CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \
./configure --prefix=/usr/local/mysql --with-low-memory
The -Wa,-many is necessary for the compile to be successful. IBM is
aware of this problem but is in to hurry to fix it because of the
workaround available. We don't know if the -fno-exceptions is required
with gcc 2.95, but as MySQL doesn't use exceptions and the
above option generates faster code, we recommend that you should always use
this option with egcs / gcc.
If you have problems with signals (MySQL dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell MySQL not to use signals by configuring with:
shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \
CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -DDONT_USE_THR_ALARM" \
./configure --prefix=/usr/local/mysql --with-debug --with-low-memory
This doesn't affect the performance of MySQL, but has the side
effect that you can't kill clients that are ``sleeping'' on a connection with
mysqladmin kill or mysqladmin shutdown. Instead, the client
will die when it issues its next command.
On some versions of AIX, linking with libbind.a makes
getservbyname core dump. This is an AIX bug and should be reported
to IBM.
There are a couple of small problems when compiling MySQL on
HP-UX. We recommend that you use gcc instead of the HP-UX native
compiler, because gcc produces better code!
We recommend using gcc 2.95 on HP-UX. Don't use high optimization flags (like -O6) as this may not be safe on HP-UX.
Note that MIT-pthreads can't be compiled with the HP-UX compiler
because it can't compile .S (assembler) files.
The following configure line should work:
CFLAGS="-DHPUX -I/opt/dce/include" CXXFLAGS="-DHPUX -I/opt/dce/include -felide-constructors -fno-exceptions -fno-rtti" CXX=gcc ./configure --with-pthread --with-named-thread-libs='-ldce' --prefix=/usr/local/mysql --disable-shared
If you are compiling gcc 2.95 yourself, you should NOT link it with
the DCE libraries (libdce.a or libcma.a) if you want to compile
MySQL with MIT-pthreads. If you mix the DCE and MIT-pthreads
packages you will get a mysqld to which you cannot connect. Remove
the DCE libraries while you compile gcc 2.95!
For HPUX Version 11.x we recommend MySQL Version 3.23.15 or later.
If you are using gcc 2.95.1 on a unpatched HPUX 11.x system,
you will get the error:
In file included from /usr/include/unistd.h:11,
from ../include/global.h:125,
from mysql_priv.h:15,
from item.cc:19:
/usr/include/sys/unistd.h:184: declaration of C function ...
/usr/include/sys/pthread.h:440: previous declaration ...
In file included from item.h:306,
from mysql_priv.h:158,
from item.cc:19:
The problem is that HP-UX doesn't define pthreads_atfork() consistently.
It has conflicting prototypes in
`/usr/include/sys/unistd.h':184 and
`/usr/include/sys/pthread.h':440 (I post the details below).
One solution is to copy `/usr/include/sys/unistd.h' into `mysql/include' and edit `unistd.h' and change it to match the definition in `pthread.h'. Here's the diff:
183,184c183,184 < extern int pthread_atfork(void (*prepare)(), void (*parent)(), < void (*child)()); --- > extern int pthread_atfork(void (*prepare)(void), void (*parent)(void), > void (*child)(void));
After this, the following configure line should work:
CFLAGS="-fomit-frame-pointer -O6 -fpic" CXX=gcc CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -O6" ./configure --prefix=/usr/local/mysql --disable-shared
Here is some information that a HPUX Version 11.x user sent us about compiling MySQL with HPUX:x compiler:
Environment:
proper compilers.
setenv CC cc
setenv CXX aCC
flags
setenv CFLAGS -D_REENTRANT
setenv CXXFLAGS -D_REENTRANT
setenv CPPFLAGS -D_REENTRANT
% aCC -V
aCC: HP ANSI C++ B3910B X.03.14.06
% cc -V /tmp/empty.c
cpp.ansi: HP92453-01 A.11.02.00 HP C Preprocessor (ANSI)
ccom: HP92453-01 A.11.01.00 HP C Compiler
cc: "/tmp/empty.c", line 1: warning 501: Empty source file.
configuration:
./configure --with-pthread \
--prefix=/source-control/mysql \
--with-named-thread-libs=-lpthread \
--with-low-memory
added '#define _CTYPE_INCLUDED' to include/m_ctype.h. This
symbol is the one defined in HP's /usr/include/ctype.h:
/* Don't include std ctype.h when this is included */
#define _CTYPE_H
#define __CTYPE_INCLUDED
#define _CTYPE_INCLUDED
#define _CTYPE_USING /* Don't put names in global namespace. */
-D_REENTRANT to get the
compiler to recognize the prototype for
localtime_r. Alternatively I could have supplied the prototype
for localtime_r. But I wanted to catch other bugs without needing
to run into them. I wasn't sure where I needed it, so I added it to all
flags.
You can get MySQL to work on Mac OS X by following the links to the Mac OS X ports. See section 1.9 Useful MySQL-related Links.
MySQL Version 3.23.7 should include all patches necessary to configure it on Mac OS X. You must, however, first install the pthread package from http://www.prnet.de/RegEx/mysql.html before configuring MySQL.
You might want to also add aliases to your shell's resource file to
access mysql and mysqladmin from the command line:
alias mysql '/usr/local/mysql/bin/mysql' alias mysqladmin '/usr/local/mysql/bin/mysqladmin'
We are really interested in getting MySQL to work on BeOS, but unfortunately we don't have any person who knows BeOS or has time to do a port.
We are interested in finding someone to do a port, and we will help them with any techincal questions they may have while doing the port.
We have previously talked with some BeOS developers that have said that MySQL is 80% ported to BeOS, but we haven't heard from these in a while.
This section describes installation and use of MySQL on Windows. This is also described in the `README' file that comes with the MySQL Windows distribution.
If you don't have a copy of the MySQL distribution, you should first download one from http://www.mysql.com/.
If you plan to connect to MySQL from some other program, you will probably also need the MyODBC driver. You can find this at the MyODBC download page (http://www.mysql.com/downloads/api-myodbc.html).
To install either distribution, unzip it in some empty directory and run the
Setup.exe program.
By default, MySQL-Windows is configured to be installed in
`C:\mysql'. If you want to install MySQL elsewhere, install it
in `C:\mysql', then move the installation to where you want it. If you
do move MySQL, you must tell mysqld where everything is by
supplying options to mysqld. Use C:\mysql\bin\mysqld --help to
display all options! For example, if you have moved the MySQL
distribution to `D:\programs\mysql', you must start mysqld with:
D:\programs\mysql\bin\mysqld --basedir D:\programs\mysql
With all newer MySQL versions, you can also create a `C:\my.cnf' file that holds any default options for the MySQL server. Copy the file `\mysql\my-xxxxx.cnf' to `C:\my.cnf' and edit this to suit your setup. Note that you should specify all paths with `/' instead of `\'. If you use `\', you need to specify this twice, as `\' is the escape character in MySQL. See section 4.16.5 Option Files.
MySQL uses TCP/IP to connect a client to a server. (This will allow any machine on your network to connect to your MySQL server.) Because of this, you must install TCP/IP on your machine before starting MySQL. You can find TCP/IP on your Windows CD-ROM.
Note that if you are using an old Win95 release (for example OSR2), it's likely that you have an old Winsock package! MySQL requires Winsock 2! You can get the newest Winsock from Microsoft. Win98 has as default the new Winsock 2 library, so the above doesn't apply for Win98.
There are 2 different MySQL servers you can use:
mysqld | Compiled with full debugging and automatic memory allocation checking |
mysqld-opt | Optimized for a Pentium processor. |
Both of the above should work on any Intel processor >= i386.
To start the mysqld server, you should start an MS-DOS window and type:
C:\mysql\bin\mysqld
This will start mysqld in the background without a window.
You can kill the MySQL server by executing:
C:\mysql\bin\mysqladmin -u root shutdown
Note that Win95/Win98 don't support creation of named pipes. On Win95/Win98, you can only use named pipes to connect to a remote MySQL running on an NT server.
If mysqld doesn't start, please check whether or not the
`\mysql\mysql.err' file contains any reason for this. You can also
try to start it with mysqld --standalone; In this case you may
get some useful information on the screen that may help solve this.
The last option is to start mysqld with --debug. In this
case mysqld will write a log file in `\mysqld.trace'
that should contain the reason why mysqld doesn't start. If you
make a bug report about this, please only send the lines to the mailing list
where something seems to go wrong!
The Win95/Win98 section also applies to MySQL on NT/Win2000, with the following differences:
To get MySQL to work with TCP/IP on NT, you must install service pack 3 (or newer)!
Note that everything in the following that applies for NT also applies for Win2000!
For NT/Win2000, the server name is mysqld-nt. Normally you
should install MySQL as a service on NT/Win2000:
C:\mysql\bin\mysqld-nt --install
(You could use the mysqld or mysqld-opt servers on NT,
but those cannot be started as a service or use named pipes.)
You can start and stop the MySQL service with:
NET START mysql NET STOP mysql
Note that in this case you can't use any other options for mysqld-nt!
You can also run mysqld-nt as a stand-alone program on NT if you need
to start mysqld-nt with any options! If you start mysqld-nt
without options on NT, mysqld-nt tries to starts itself as a service
with the default service options. If you have stopped mysqld-nt, you
have to start it with NET START mysql.
The service is installed with the name MySql. Once installed, it must
be started using the Services Control Manager (SCM) Utility (found in Control
Panel) or by using the NET START MySQL command. If any options are
desired, they must be specified as "Startup parameters" in the SCM utility
before you start the MySQL service. Once running, mysqld-nt
can be stopped using mysqladmin or from the SCM utility or by using
the command NET STOP MySQL. If you use SCM to stop mysqld-nt,
there is a strange message from SCM about mysqld shutdown normally.
When run as a service, mysqld-nt has no access to a console and so no
messages can be seen.
On NT you can get the following service error messages:
| Permission Denied | Means that it cannot find mysqld-nt.exe.
|
| Cannot Register | Means that the path is incorrect. |
If you have problems installing mysqld-nt as a service, try starting
it with the full path:
C:\mysql\bin\mysqld-nt --install
If this doesn't work, you can get mysqld-nt to start properly by fixing
the path in the registry!
If you don't want to start mysqld-nt as a service, you can start it as
follows:
C:\mysql\bin\mysqld-nt --standalone
or
C:\mysql\bin\mysqld --standalone --debug
The last version gives you a debug trace in `C:\mysqld.trace'.
MySQL supports TCP/IP on all Windows platforms and named pipes on NT. The default is to use named pipes for local connections on NT and TCP/IP for all other cases if the client has TCP/IP installed. The host name specifies which protocol is used:
| Protocol | |
| NULL (none) | On NT, try named pipes first; if that doesn't work, use TCP/IP. On Win95/Win98, TCP/IP is used. |
| . | Named pipes |
| localhost | TCP/IP to current host |
| hostname | TCP/IP |
You can force a MySQL client to use named pipes by specifying the
--pipe option. Use the --socket option to specify the name of
the pipe.
You can test whether or not MySQL is working by executing the following commands:
C:\mysql\bin\mysqlshow C:\mysql\bin\mysqlshow -u root mysql C:\mysql\bin\mysqladmin version status proc C:\mysql\bin\mysql test
If mysqld is slow to answer to connections on Win95/Win98, there is
probably a problem with your DNS. In this case, start mysqld with
--skip-name-resolve and use only localhost and IP numbers in
the MySQL grant tables. You can also avoid DNS when connecting to a
mysqld-nt MySQL server running on NT by using the
--pipe argument to specify use of named pipes. This works for most
MySQL clients.
There are two versions of the MySQL command-line tool:
mysql | Compiled on native Windows, which offers very limited text editing capabilities. |
mysqlc | Compiled with the Cygnus GNU compiler and libraries, which offers readline editing.
|
If you want to use mysqlc.exe, you must copy
`C:\mysql\lib\cygwinb19.dll' to `\windows\system' (or similar
place).
The default privileges on Windows give all local users full privileges
to all databases. To make MySQL more secure, you
should set a password for all users and remove the row in the
mysql.user table that has Host='localhost' and
User=''.
You should also add a password for the root user.
(The following example starts by removing the anonymous user, that allows
anyone to access the 'test' database.):
C:\mysql\bin\mysql mysql mysql> DELETE FROM user WHERE Host='localhost' AND User=''; mysql> QUIT C:\mysql\bin\mysqladmin reload C:\mysql\bin\mysqladmin -u root password your_password
After you've set the password, if you want to take down the mysqld
server, you can do so using this command:
mysqladmin --user=root --password=your_password shutdown
If you are using the old shareware version of MySQL Version 3.21
under Windows, the above command will fail with an error: parse error
near 'SET OPTION password'. This is because the old shareware version,
which is based on MySQL Version 3.21, doesn't have the
SET PASSWORD command. The fix is in this case to upgrade to
the Version 3.22 shareware.
With the newer MySQL versions you can easily add new users
and change privileges with GRANT and REVOKE commands.
See section 7.34 GRANT and REVOKE Syntax.
Here is a note about how to connect to get a secure connection to remote MySQL server with SSH (by David Carlson):
local port: 3306,
host: localhost, remote port: 3306.
That's it. It works very well with a direct Internet connection. I'm having problems with SSH conflicting with my Win95 network and Wingate - but that'll be the topic of a posting on another software company's usegroup!
On windows MySQL Version 3.23.16 and above is compiled with the
-DUSE_SYMDIR option. This allows you to put a database on
different disk by adding a symbolic link to it (in a similar manner that
symbolic links works on Unix).
On windows you make a symbolic link to a database by creating a file
that contains the path to the destination directory and saving this in
the mysql_data directory under the filename database.sym.
Note that the symbolic link will only be used if the directory
mysql_data_dir\database doesn't exist.
For example, if you want to have database foo on `D:\data\foo', you
should create the file `C:\mysql\data\foo.sym' that contains the
text D:\data\foo. After this, all tables created in the database
foo will be created in `D:\data\foo'.
In your source files, you should include `windows.h' before you include
mysql.h:
#if defined(_WIN32) || defined(_WIN64) #include <windows.h> #endif #include <mysql.h>
You can either link your code with the dynamic `libmysql.lib' library, which is just a wrapper to load in `libmysql.dll' on demand, or link with the static `mysqlclient.lib' library.
Note that as the mysqlclient libraries are compiled as threaded libraries, you should also compile your code to be multi-threaded!
We will shortly do a full test on the new BDB interface on Windows. When this is done we will start to release binary distributions (for Windows and Unix) of MySQL that will include support for BDB tables.
MySQL-Windows has by now proven itself to be very stable. This version of MySQL has the same features as the corresponding Unix version with the following exceptions:
mysqld for an extended time on Win95 if
you do many connections, because each connection in MySQL creates
a new thread! WinNT and Win98 don't suffer from this bug.
pread() and pwrite() calls to be
able to mix INSERT and SELECT. Currently we use mutexes
to emulate pread()/pwrite(). We will, in the long run,
replace the file level interface with a virtual interface so that we can
use the readfile()/writefile() interface on NT to get more speed.
The current implementation will however limit the number of open files
MySQL can use to 1024, which means that you will not be able to
run as many concurrent threads on NT as on Unix.
mysqladmin kill will not work on a sleeping connection.
mysqladmin shutdown can't abort as long as there are sleeping
connections.
DROP DATABASE
mysqladmin shutdown.
my_table and as
MY_TABLE:
SELECT * FROM my_table WHERE MY_TABLE.col=1;
LOAD
DATA INFILE or SELECT ... INTO OUTFILE, you must double the `\'
character or use Unix style filenames `/' characters:
LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr; SELECT * INTO OUTFILE 'C:/tmp/skr.txt' FROM skr;
Can't open named pipe error
error 2017: can't open named pipe to host: . pipe...This is because the release version of MySQL uses named pipes on NT by default. You can avoid this error by using the
--host=localhost option to the new MySQL clients
or create a file `C:\my.cnf' that contains the following information:
[client] host = localhost
Access denied for user error
Access denied for user: 'some-user@unknown'
to database 'mysql' when accessing a MySQL server on the same
machine, this means that MySQL can't resolve your host name
properly.
To fix this, you should create a file `\windows\hosts' with the
following information:
127.0.0.1 localhost
ALTER TABLE
ALTER TABLE the table is locked from usage
by other threads. This has to do with the fact that you on Windows can't
delete a file that is in use by another threads. (We may in the future
find some way to go around this problem).
Here are some open issues for anyone who might want to help us with the Windows release:
MYSQL.DLL server. This should include everything in
a standard MySQL server, except thread creation. This will make
MySQL much easier to use in applications that don't need a true
client/server and don't need to access the server from other hosts.
mysqld.cc,
but it should be recoded to be more parameter oriented.
The tool should also be able to update the `\my.cnf' file if the user
prefers to use this instead of the registry.
mysqld as a service with --install (on NT)
it would be nice if you could also add default options on the command line.
For the moment, the workaround is to update the `C:\my.cnf' file
instead.
mysqld
daemon doesn't accept new connections when the laptop is resumed.
We don't know if this is a problem with Win95, TCP/IP, or MySQL.
mysqld from the
task manager. For the moment, you must use mysqladmin shutdown.
readline to Windows for use in the mysql command line tool.
mysql,
mysqlshow, mysqladmin, and mysqldump) would be nice.
mysqladmin kill on Windows.
mysqld always starts in the "C" locale and not in the default locale.
We would like to have mysqld use the current locale for the sort order.
.DLLs.
Other Windows-specific issues are described in the `README' file that comes with the MySQL-Windows distribution.
MySQL uses quite a few open files. Because of this, you should add something like the following to your `CONFIG.SYS' file:
SET EMXOPT=-c -n -h1024
If you don't do this, you will probably run into the following error:
File 'xxxx' not found (Errcode: 24)
When using MySQL with OS/2 Warp 3, FixPack 29 or above is required. With OS/2 Warp 4, FixPack 4 or above is required. This is a requirement of the Pthreads library. MySQL must be installed in a partition that supports long filenames such as HPFS, FAT32, etc.
The `INSTALL.CMD' script must be run from OS/2's own `CMD.EXE' and may not work with replacement shells such as `4OS2.EXE'.
The `scripts/mysql-install-db' script has been renamed. It is now called `install.cmd' and is a REXX script, which will set up the default MySQL security settings and create the WorkPlace Shell icons for MySQL.
Dynamic module support is compiled in but not fully tested. Dynamic modules should be compiled using the Pthreads run-time library.
gcc -Zdll -Zmt -Zcrtdll=pthrdrtl -I../include -I../regex -I.. \
-o example udf_example.cc -L../lib -lmysqlclient udf_example.def
mv example.dll example.udf
Note: Due to limitations in OS/2, UDF module name stems must not
exceed 8 characters. Modules are stored in the `/mysql2/udf'
directory; the safe-mysqld.cmd script will put this directory in
the BEGINLIBPATH environment variable. When using UDF modules,
specified extensions are ignored -- it is assumed to be `.udf'.
For example, in Unix, the shared module might be named `example.so'
and you would load a function from it like this:
CREATE FUNCTION metaphon RETURNS STRING SONAME "example.so";
Is OS/2, the module would be named `example.udf', but you would not specify the module extension:
CREATE FUNCTION metaphon RETURNS STRING SONAME "example";
As a service, we at MySQL AB provides a set of binary distributions of MySQL that are compiled at our site or at sites where customers kindly have given us access to their machines.
These distributions are generated with
scripts/make_binary_distribution and are configured with the
following compilers and options:
gcc 2.7.2.1
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --disable-shared --with-extra-charsets=complex
egcs 1.0.3a
CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex
egcs 2.90.27
CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex
gcc 2.8.1
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex
pgcc 2.90.29 (egcs 1.0.3a)
CFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --with-extra-charsets=complex
gcc 2.95.2
CFLAGS="-O6 -mpentiumpro -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -mpentiumpro -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-extra-charset=complex
gcc 2.7-95q4
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex
gcc 2.7.2.2
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex
gcc 2.8.1
CC=gcc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory --with-extra-charsets=complex
gcc 2.8.0
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex
gcc 2.7.2.1
CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex
gcc 2.7.2
CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-extra-charsets=complex
Anyone who has more optimal options for any of the configurations listed above can always mail them to the developer's mailing list at internals@lists.mysql.com.
RPM distributions prior to MySQL Version 3.22 are user-contributed. Beginning with Version 3.22, some RPMs are generated by us at MySQL AB.
If you want to compile a debug version of MySQL, you should add
--with-debug or --with-debug=full to the above configure lines
and remove any -fomit-frame-pointer options.
Once you've installed MySQL (from either a binary or source distribution), you need to initialize the grant tables, start the server, and make sure that the server works okay. You may also wish to arrange for the server to be started and stopped automatically when your system starts up and shuts down.
Normally you install the grant tables and start the server like this for installation from a source distribution:
shell> ./scripts/mysql_install_db shell> cd mysql_installation_directory shell> ./bin/safe_mysqld --user=mysql &
For a binary distribution, do this:
shell> cd mysql_installation_directory shell> ./bin/mysql_install_db shell> ./bin/safe_mysqld --user=mysql &
Testing is most easily done from the top-level directory of the MySQL distribution. For a binary distribution, this is your installation directory (typically something like `/usr/local/mysql'). For a source distribution, this is the main directory of your MySQL source tree.
In the commands shown below in this section and in the following
subsections, BINDIR is the path to the location in which programs
like mysqladmin and safe_mysqld are installed. For a
binary distribution, this is the `bin' directory within the
distribution. For a source distribution, BINDIR is probably
`/usr/local/bin', unless you specified an installation directory
other than `/usr/local' when you ran configure.
EXECDIR is the location in which the mysqld server is
installed. For a binary distribution, this is the same as
BINDIR. For a source distribution, EXECDIR is probably
`/usr/local/libexec'.
Testing is described in detail below:
mysqld server and set up the initial
MySQL grant tables containing the privileges that determine how
users are allowed to connect to the server. This is normally done with the
mysql_install_db script:
shell> scripts/mysql_install_dbTypically,
mysql_install_db needs to be run only the first time you
install MySQL. Therefore, if you are upgrading an existing
installation, you can skip this step. (However, mysql_install_db is
quite safe to use and will not update any tables that already exist, so if
you are unsure of what to do, you can always run mysql_install_db.)
mysql_install_db creates six tables (user, db,
host, tables_priv, columns_priv, and func) in the
mysql database. A description of the initial privileges is given in
section 6.12 Setting Up the Initial MySQL Privileges. Briefly, these privileges allow the MySQL
root user to do anything, and allow anybody to create or use databases
with a name of 'test' or starting with 'test_'.
If you don't set up the grant tables, the following error will appear in the
log file when you start the server:
mysqld: Can't find file: 'host.frm'The above may also happen with a binary MySQL distribution if you don't start MySQL by executing exactly
./bin/safe_mysqld!
See section 14.2 safe_mysqld, the wrapper around mysqld.
You might need to run mysql_install_db as root. However,
if you prefer, you can run the MySQL server as an unprivileged
(non-root) user, provided that user can read and write files in
the database directory. Instructions for running MySQL as an
unprivileged user are given in section 20.10 How to Run MySQL As a Normal User.
If you have problems with mysql_install_db, see
section 4.16.1 Problems Running mysql_install_db.
There are some alternatives to running the mysql_install_db
script as it is provided in the MySQL distribution:
mysql_install_db before running it, to
change the initial privileges that are installed into the grant tables.
This is useful if you want to install MySQL on a lot of machines
with the same privileges. In this case you probably should need only to add
a few extra INSERT statements to the mysql.user and
mysql.db tables!
mysql_install_db, then use mysql -u root mysql to
connect to the grant tables as the MySQL root user and issue
SQL statements to modify the grant tables directly.
mysql_install_db.
shell> cd mysql_installation_directory shell> bin/safe_mysqld &If you have problems starting the server, see section 4.16.2 Problems Starting the MySQL Server.
mysqladmin to verify that the server is running. The following
commands provide a simple test to check that the server is up and responding
to connections:
shell> BINDIR/mysqladmin version shell> BINDIR/mysqladmin variablesThe output from
mysqladmin version varies slightly depending on your
platform and version of MySQL, but should be similar to that shown
below:
shell> BINDIR/mysqladmin version mysqladmin Ver 6.3 Distrib 3.22.9-beta, for pc-linux-gnu on i686 TCX Datakonsult AB, by Monty Server version 3.22.9-beta Protocol version 10 Connection Localhost via Unix socket TCP port 3306 UNIX socket /tmp/mysql.sock Uptime: 16 sec Running threads: 1 Questions: 20 Reloads: 2 Open tables: 3To get a feeling for what else you can do with
BINDIR/mysqladmin,
invoke it with the --help option.
shell> BINDIR/mysqladmin -u root shutdown
safe_mysqld or
by invoking mysqld directly. For example:
shell> BINDIR/safe_mysqld --log &If
safe_mysqld fails, try running it from the MySQL
installation directory (if you are not already there). If that doesn't work,
see section 4.16.2 Problems Starting the MySQL Server.
shell> BINDIR/mysqlshow +-----------+ | Databases | +-----------+ | mysql | +-----------+ shell> BINDIR/mysqlshow mysql Database: mysql +--------------+ | Tables | +--------------+ | columns_priv | | db | | func | | host | | tables_priv | | user | +--------------+ shell> BINDIR/mysql -e "select host,db,user from db" mysql +------+--------+------+ | host | db | user | +------+--------+------+ | % | test | | | % | test_% | | +------+--------+------+There is also a benchmark suite in the `sql-bench' directory (under the MySQL installation directory) that you can use to compare how MySQL performs on different platforms. The `sql-bench/Results' directory contains the results from many runs against different databases and platforms. To run all tests, execute these commands:
shell> cd sql-bench shell> run-all-testsIf you don't have the `sql-bench' directory, you are probably using an RPM for a binary distribution. (Source distribution RPMs include the benchmark directory.) In this case, you must first install the benchmark suite before you can use it. Beginning with MySQL Version 3.22, there are benchmark RPM files named `mysql-bench-VERSION-i386.rpm' that contain benchmark code and data. If you have a source distribution, you can also run the tests in the `tests' subdirectory. For example, to run `auto_increment.tst', do this:
shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tstThe expected results are shown in the `./tests/auto_increment.res' file.
mysql_install_db
The purpose of the mysql_install_db script is to generate new
MySQL privilege tables. It will not affect any other data!
It will also not do anything if you already have MySQL privilege
tables installed!
If you want to re-create your privilege tables, you should take down the mysqld server, if it's running, and then do something like:
mv mysql-data-directory/mysql mysql-data-directory/mysql-old mysql_install_db
This section lists problems you might encounter when you run
mysql_install_db:
mysql_install_db doesn't install the grant tables
mysql_install_db fails to install the grant
tables and terminates after displaying the following messages:
starting mysqld daemon with databases from XXXXXX mysql daemon endedIn this case, you should examine the log file very carefully! The log should be located in the directory `XXXXXX' named by the error message, and should indicate why
mysqld didn't start. If you don't understand
what happened, include the log when you post a bug report using
mysqlbug!
See section 2.3 How to Report Bugs or Problems.
mysqld daemon running
mysql_install_db at
all. You have to run mysql_install_db only once, when you install
MySQL the first time.
mysqld daemon doesn't work when one daemon is running
Can't start server: Bind on
TCP/IP port: Address already in use or Can't start server : Bind on
unix socket... You can start the new server with a different socket and
port as follows:
shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock shell> MYSQL_TCP_PORT=3307 shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT shell> scripts/mysql_install_db shell> bin/safe_mysqld &The environment variables appendix includes a list of other environment variables you can use to affect
mysqld. See section A Environment Variables.
After this, you should edit your server boot script to start both daemons
with different sockets and ports. For example, it could invoke
safe_mysqld twice, but with different --socket, --port,
and --basedir options for each invocation.
mysql_install_db or when
starting or using mysqld.
You can specify a different socket and temporary directory as follows:
shell> TMPDIR=/some_tmp_dir/ shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock shell> export TMPDIR MYSQL_UNIX_PORT`some_tmp_dir' should be the path to some directory for which you have write permission. See section A Environment Variables. After this you should be able to run
mysql_install_db and start
the server with these commands:
shell> scripts/mysql_install_db shell> BINDIR/safe_mysqld &
mysqld crashes immediately
glibc older than
2.0.7-5, you should make sure you have installed all glibc patches!
There is a lot of information about this in the MySQL mail
archives. Links to the mail archives are available at the online
MySQL documentation page.
Also, see section 4.12.5 Linux Notes (All Linux Versions).
You can also start mysqld manually using the --skip-grant-tables
option and add the privilege information yourself using mysql:
shell> BINDIR/safe_mysqld --skip-grant-tables & shell> BINDIR/mysql -u root mysqlFrom
mysql, manually execute the SQL commands in
mysql_install_db. Make sure you run mysqladmin
flush-privileges or mysqladmin reload afterward to tell the server to
reload the grant tables.
Generally, you start the mysqld server in one of three ways:
mysql.server. This script is used primarily at
system startup and shutdown, and is described more fully in
section 4.16.3 Starting and Stopping MySQL Automatically.
safe_mysqld, which tries to determine the proper options
for mysqld and then runs it with those options. See section 14.2 safe_mysqld, the wrapper around mysqld.
mysqld as a service as follows:
bin\mysqld-nt --install # Install MySQL as a serviceYou can now start/stop
mysqld as follows:
NET START mysql NET STOP mysqlNote that in this case you can't use any other options for
mysqld!
You can remove the service as follows:
bin\mysqld-nt --remove # remove MySQL as a service
mysqld directly.
When the mysqld daemon starts up, it changes directory to the
data directory. This is where it expects to write log files and the pid
(process ID) file, and where it expects to find databases.
The data directory location is hardwired in when the distribution is
compiled. However, if mysqld expects to find the data directory
somewhere other than where it really is on your system, it will not work
properly. If you have problems with incorrect paths, you can find out
what options mysqld allows and what the default path settings are by
invoking mysqld with the --help option. You can override the
defaults by specifying the correct pathnames as command-line arguments to
mysqld. (These options can be used with safe_mysqld as well.)
Normally you should need to tell mysqld only the base directory under
which MySQL is installed. You can do this with the --basedir
option. You can also use --help to check the effect of changing path
options (note that --help must be the final option of the
mysqld command). For example:
shell> EXECDIR/mysqld --basedir=/usr/local --help
Once you determine the path settings you want, start the server without
the --help option.
Whichever method you use to start the server, if it fails to start up
correctly, check the log file to see if you can find out why. Log files
are located in the data directory (typically
`/usr/local/mysql/data' for a binary distribution,
`/usr/local/var' for a source distribution,
`\mysql\mysql.err' on Windows.) Look in the data directory for
files with names of the form `host_name.err' and
`host_name.log' where host_name is the name of your server
host. Then check the last few lines of these files:
shell> tail host_name.err shell> tail host_name.log
If you find something like the following in the log file:
000729 14:50:10 bdb: Recovery function for LSN 1 27595 failed 000729 14:50:10 bdb: warning: ./test/t1.db: No such file or directory 000729 14:50:10 Can't init databases
this means that you started mysqld with --bdb-recover and that
Berkeley DB found something wrong with it's log files when it tried to
recover your databases. To be able to continue, you should move away
the old Berkeley DB log file from the database directory to some other
place, where you can later examine these. The log files are named
`log.0000000001', where the number will increase over time.
If you get the following error, it means that some other program (or another
mysqld server) is already using the TCP/IP port or socket
mysqld is trying to use:
Can't start server: Bind on TCP/IP port: Address already in use or Can't start server : Bind on unix socket...
Use ps to make sure that you don't have another mysqld server
running. If you can't find another server running, you can try to execute
the command telnet your-host-name tcp-ip-port-number and press
RETURN a couple of times. If you don't get an error message like
telnet: Unable to connect to remote host: Connection refused,
something is using the TCP/IP port mysqld is trying to use.
See section 4.16.1 Problems Running mysql_install_db and section 21.6 Running Multiple MySQL Servers on the Same Machine.
If mysqld is currently running, you can find out what path settings
it is using by executing this command:
shell> mysqladmin variables or shell> mysqladmin -h 'your-host-name' variables
If safe_mysqld starts the server but you can't connect to it,
you should make sure you have an entry in `/etc/hosts' that looks like
this:
127.0.0.1 localhost
This problem occurs only on systems that don't have a working thread library and for which MySQL must be configured to use MIT-pthreads.
On Windows, you can try to start mysqld as follows:
C:\mysql\bin\mysqld --standalone --debug
This will not run in the background and it should also write a trace in `\mysqld.trace', which may help you determine the source of your problems. See section 4.13 Windows Notes.
If you are using BDB (Berkeley DB) tables, you should familiarize yourself with the different BDB specific startup options. See section 8.5.3 BDB startup options.
The mysql.server script can be used to start or stop the server
by invoking it with start or stop arguments:
shell> mysql.server start shell> mysql.server stop
mysql.server can be found in the `share/mysql' directory
under the MySQL installation directory or in the `support-files'
directory of the MySQL source tree.
Before mysql.server starts the server, it changes directory to
the MySQL installation directory, then invokes
safe_mysqld. You might need to edit mysql.server if you
have a binary distribution that you've installed in a non-standard
location. Modify it to cd into the proper directory before it
runs safe_mysqld. If you want the server to run as some specific
user, you can change the mysql_daemon_user=root line to use
another user. You can also modify mysql.server to pass other
options to safe_mysqld.
mysql.server stop brings down the server by sending a signal to it.
You can take down the server manually by executing mysqladmin shutdown.
You might want to add these start and stop commands to the appropriate places
in your `/etc/rc*' files when you start using MySQL for
production applications. Note that if you modify mysql.server, then
upgrade MySQL sometime, your modified version will be overwritten,
so you should make a copy of your edited version that you can reinstall.
If your system uses `/etc/rc.local' to start external scripts, you should append the following to it:
/bin/sh -c 'cd /usr/local/mysql ; ./bin/safe_mysqld --user=mysql &'
You can also add options for mysql.server in a global
`/etc/my.cnf' file. A typical `/etc/my.cnf' file might look like
this:
[mysqld] datadir=/usr/local/mysql/var socket=/tmp/mysqld.sock port=3306 [mysql.server] user=mysql basedir=/usr/local/mysql
The mysql.server script uses the following variables:
user, datadir, basedir, bindir, and
pid-file.
See section 4.16.5 Option Files.
mysqld accepts the following command-line options:
--ansi
-b, --basedir=path
--big-tables
--bind-address=IP
--character-sets-dir=path
--chroot=path
LOAD DATA INFILE
and SELECT ... INTO OUTFILE though.
-h, --datadir=path
--default-character-set=charset
--default-table-type=type
--delay-key-write-for-all-tables
MyISAM table.
See section 12.2.3 Tuning Server Parameters.
--enable-locking
-T, --exit-info
--flush
-?, --help
--init-file=file
-L, --language=...
-l, --log[=file]
--log-isam[=file]
--log-slow-queries[=file]
long_query_time seconds to
execute to file. See section 21.5 The Slow Query Log.
--log-update[=file]
file.# where # is a unique number if not given.
See section 21.3 The Update Log.
--log-long-format
--log-slow-queries then queries that are not using indexes are logged
to the slow query log.
--low-priority-updates
INSERT/DELETE/UPDATE)
will have lower priority than selects.
It can also be done via {INSERT | REPLACE | UPDATE | DELETE}
LOW_PRIORITY ... to lower the priority of only one query, or by
SET OPTION SQL_LOW_PRIORITY_UPDATES=1 to change the
priority in one thread.
See section 12.2.9 Table Locking Issues.
--memlock
mysqld process in memory. This works only if your system
supports the mlockall() system call. This may help if you have
a problem where the operating system is causing mysqld to swap on disk.
--myisam-recover [=option[,option...]]] where option is one of DEFAULT, BACKUP, FORCE or QUICK.
mysqld will on open check if the table is
marked as crashed or if if the table wasn't closed properly
(The last option only works if you are running with --skip-locking).
If this is the case mysqld will run check on the table. If the table was
corrupted, mysqld will attempt to repair it.
The following options affects how the repair works.
| DEFAULT | The same as not giving any option to --myisam-recover.
|
| BACKUP | If the data table was changed during recover, save a backup of the `table_name.MYD' data file as `table_name-datetime.BAK'. |
| FORCE | Run recover even if we will loose more than one row from the .MYD file. |
| QUICK | Don't check the rows in the table if there isn't any delete blocks. |
BACKUP,FORCE. This will force a repair of a table even if some rows
would be deleted, but it will keep the old data file as a backup so that
you can later examine what happened.
--pid-file=path
safe_mysqld.
-P, --port=...
-o, --old-protocol
--one-thread
-O, --set-variable var=option
--help lists variables.
You can find a full description for all variables in the SHOW VARIABLES
section in this manual. See section 7.28.4 SHOW VARIABLES.
The tuning server parameters section includes information of how to optimize
these. See section 12.2.3 Tuning Server Parameters.
-Sg, --skip-grant-tables
mysqladmin
flush-privileges or mysqladmin reload.)
--safe-mode
--skip-delay-key-write.
--secure
gethostbyname() system call are
checked to make sure they resolve back to the original hostname. This
makes it harder for someone on the outside to get access by pretending
to be another host. This option also adds some sanity checks of
hostnames. The option is turned off by default in MySQL Version 3.21
because sometimes it takes a long time to perform backward resolutions.
MySQL Version 3.22 caches hostnames (unless --skip-host-cache
is used) and has this option enabled by default.
--skip-concurrent-insert
MyISAM
tables. (This is only to be used if you think you have found a bug
in this feature).
--skip-delay-key-write
delay_key_write option for all tables.
See section 12.2.3 Tuning Server Parameters.
--skip-locking
isamchk or myisamchk you must
shut down the server. See section 1.6 How Stable Is MySQL?. Note that in MySQL Version
3.23 you can use REPAIR and CHECK to repair/check MyISAM
tables.
--skip-name-resolve
Host column values in the grant
tables must be IP numbers or localhost.
--skip-networking
mysqld must be made via Unix sockets.
This option is highly recommended for systems where only local requests
are allowed. However, this option is unsuitable for systems that use
MIT-pthreads, because the MIT-pthreads package doesn't support Unix
sockets.
--skip-new
--skip-delay-key-write.
This will also set default table type to ISAM. See section 8.3 ISAM Tables.
--skip-host-cache
--skip-show-database
--skip-thread-priority
--socket=path
/tmp/mysql.sock.
-t, --tmpdir=path
/tmp
directory resides on a partition too small to hold temporary tables.
-u, --user=user_name
mysqld daemon as user user_name. This option is
mandatory when starting mysqld as root.
-V, --version
MySQL Version 3.22 can read default startup options for the server and for clients from option files.
MySQL reads default options from the following files on Unix:
| Filename | Purpose |
/etc/my.cnf | Global options |
DATADIR/my.cnf | Server-specific options |
defaults-extra-file | The file specified with --defaults-extra-file=# |
~/.my.cnf | User-specific options |
DATADIR is the MySQL data directory (typically
`/usr/local/mysql/data' for a binary installation or
`/usr/local/var' for a source installation). Note that this is the
directory that was specified at configuration time, not the one specified
with --datadir when mysqld starts up! (--datadir has no
effect on where the server looks for option files, because it looks for them
before it processes any command-line arguments.)
MySQL reads default options from the following files on Windows:
| Filename | Purpose |
windows-system-directory\my.ini | Global options |
C:\my.cnf | Global options |
C:\mysql\data\my.cnf | Server-specific options |
Note that on Windows, you should specify all paths with / instead of
\. If you use \, you need to specify this twice, as
\ is the escape character in MySQL.
MySQL tries to read option files in the order listed above. If multiple option files exist, an option specified in a file read later takes precedence over the same option specified in a file read earlier. Options specified on the command line take precedence over options specified in any option file. Some options can be specified using environment variables. Options specified on the command line or in option files take precedence over environment variable values. See section A Environment Variables.
The following programs support option files: mysql,
mysqladmin, mysqld, mysqldump, mysqlimport,
mysql.server, myisamchk, and myisampack.
You can use option files to specify any long option that a program supports!
Run the program with --help to get a list of available options.
An option file can contain lines of the following forms:
#comment
[group]
group is the name of the program or group for which you want to set
options. After a group line, any option or set-variable lines
apply to the named group until the end of the option file or another group
line is given.
option
--option on the command line.
option=value
--option=value on the command line.
set-variable = variable=value
--set-variable variable=value on the command line.
This syntax must be used to set a mysqld variable.
The client group allows you to specify options that apply to all
MySQL clients (not mysqld). This is the perfect group to use
to specify the password you use to connect to the server. (But make
sure the option file is readable and writable only to yourself.)
Note that for options and values, all leading and trailing blanks are automatically deleted. You may use the escape sequences `\b', `\t', `\n', `\r', `\\', and `\s' in your value string (`\s' == blank).
Here is a typical global option file:
[client] port=3306 socket=/tmp/mysql.sock [mysqld] port=3306 socket=/tmp/mysql.sock set-variable = key_buffer_size=16M set-variable = max_allowed_packet=1M [mysqldump] quick
Here is typical user option file:
[client] # The following password will be sent to all standard MySQL clients password=my_password [mysql] no-auto-rehash set-variable = connect_timeout=2 [mysql-hot-copy] interactive-timeout
If you have a source distribution, you will find sample configuration
files named `my-xxxx.cnf' in the `support-files' directory.
If you have a binary distribution, look in the `DIR/share/mysql'
directory, where DIR is the pathname to the MySQL
installation directory (typically `/usr/local/mysql'). Currently
there are sample configuration files for small, medium, large, and very
large systems. You can copy `my-xxxx.cnf' to your home directory
(rename the copy to `.my.cnf') to experiment with this.
All MySQL clients that support option files support the following options:
| --no-defaults | Don't read any option files. |
| --print-defaults | Print the program name and all options that it will get. |
| --defaults-file=full-path-to-default-file | Only use the given configuration file. |
| --defaults-extra-file=full-path-to-default-file | Read this configuration file after the global configuration file but before the user configuration file. |
Note that the above options must be first on the command line to work!
--print-defaults may however be used directly after the
--defaults-xxx-file commands.
Note for developers: Option file handling is implemented simply by processing all matching options (that is, options in the appropriate group) before any command-line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have an old program that handles multiply-specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard MySQL clients to see how to do this.
In shell scripts you can use the `my_print_defaults' command to parse the config files:
shell> my_print_defaults client mysql --port=3306 --socket=/tmp/mysql.sock --no-auto-rehash
The above output contains all options for the groups 'client' and 'mysql'.
You can always move the MySQL form and data files between
different versions on the same architecture as long as you have the same
base version of MySQL. The current base version is
3. If you change the character set when running MySQL (which may
also change the sort order), you must run myisamchk -r -q on all
tables. Otherwise your indexes may not be ordered correctly.
If you are afraid of new versions, you can always rename your old
mysqld to something like mysqld-'old-version-number'. If
your new mysqld then does something unexpected, you can simply shut it
down and restart with your old mysqld!
When you do an upgrade you should also back up your old databases, of course.
If after an upgrade, you experience problems with recompiled client programs,
like Commands out of sync or unexpected core dumps, you probably have
used an old header or library file when compiling your programs. In this
case you should check the date for your `mysql.h' file and
`libmysqlclient.a' library to verify that they are from the new
MySQL distribution. If not, please recompile your programs!
If you get some problems that the new mysqld server doesn't want to
start or that you can't connect without a password, check that you don't
have some old `my.cnf' file from your old installation! You can
check this with: program-name --print-defaults. If this outputs
anything other than the program name, you have an active my.cnf
file that will may affect things!
It is a good idea to rebuild and reinstall the Msql-Mysql-modules
distribution whenever you install a new release of MySQL,
particularly if you notice symptoms such as all your DBI scripts
dumping core after you upgrade MySQL.
MySQL Version 3.23 supports tables of the new MyISAM type and
the old ISAM type. You don't have to convert your old tables to
use these with Version 3.23. By default, all new tables will be created with
type MyISAM (unless you start mysqld with the
--default-table-type=isam option). You can change an ISAM
table to a MyISAM table with ALTER TABLE or the Perl script
mysql_convert_table_format.
Version 3.22 and 3.21 clients will work without any problems with a Version 3.23 server.
The following lists tell what you have to watch out for when upgrading to Version 3.23:
DROP DATABASE on a symbolic linked database, both the
link and the original database is deleted. (This didn't happen in 3.22
because configure didn't detect the readlink system call).
OPTIMIZE TABLE now only works for MyISAM tables.
For other table types, you can use ALTER TABLE to optimize the table.
During OPTIMIZE TABLE the table is now locked from other threads.
mysql is now by default started with the
option --no-named-commands (-g). This option can be disabled with
--enable-named-commands (-G). This may cause incompatibility problems in
some cases, for example in SQL scripts that use named commands without a
semicolon! Long format commands still work from the first line.
german character sort order, you must repair
all your tables with isamchk -r, as we have made some changes in
the sort order!
IF will now depend on both arguments
and not only the first argument.
AUTO_INCREMENT will not work with negative numbers.
INNER, DELAYED, RIGHT, CASE, THEN, WHEN, ELSE, END and WHEN are now reserved words.
FLOAT(X) is now a true floating-point type and not a value with
a fixed number of decimals.
DECIMAL(length,dec) the length argument no
longer includes a place for the sign or the decimal point.
TIME string must now be of one of the following formats:
[[[DAYS] [H]H:]MM:]SS[.fraction] or
[[[[[H]H]H]H]MM]SS[.fraction]
LIKE now compares strings using the same character
comparison rules as '='. If you require the old behavior, you
can compile MySQL with the CXXFLAGS=-DLIKE_CMP_TOUPPER
flag.
REGEXP is now case insensitive for normal (not binary) strings.
CHECK TABLE
or myisamchk for MyISAM tables (.MYI) and
isamchk for ISAM (.ISM) tables.
mysqldump files to be compatible between
MySQL Version 3.22 and Version 3.23, you should not use the
--opt or --full option to mysqldump.
DATE_FORMAT() to make sure there is a
`%' before each format character. (Later MySQL Version 3.22
did allow this syntax.)
mysql_fetch_fields_direct is now a function (it was a macro) and
it returns a pointer to a MYSQL_FIELD instead of a
MYSQL_FIELD.
mysql_num_fields() can no longer be used on a MYSQL* object (it's
now a function that takes MYSQL_RES* as an argument. You should now
use mysql_field_count() instead.
SELECT DISTINCT ... was
almost always sorted. In Version 3.23, you must use GROUP BY or
ORDER BY to obtain sorted output.
SUM() now returns NULL, instead of 0, if there is no matching
rows. This is according to ANSI SQL.
AND or OR with NULL values will now return
NULL instead of 0. This mostly affects queries that use NOT
on an AND/OR expression as NOT NULL = NULL.
LPAD() and RPAD() will shorten the result string if it's longer
than the length argument.
Nothing that affects compatibility has changed between Version 3.21 and 3.22.
The only pitfall is that new tables that are created with DATE type
columns will use the new way to store the date. You can't access these new
fields from an old version of mysqld.
After installing MySQL Version 3.22, you should start the new server
and then run the mysql_fix_privilege_tables script. This will add the
new privileges that you need to use the GRANT command. If you forget
this, you will get Access denied when you try to use ALTER
TABLE, CREATE INDEX, or DROP INDEX. If your MySQL root
user requires a password, you should give this as an argument to
mysql_fix_privilege_tables.
The C API interface to mysql_real_connect() has changed. If you have
an old client program that calls this function, you must place a 0 for
the new db argument (or recode the client to send the db
element for faster connections). You must also call mysql_init()
before calling mysql_real_connect()! This change was done to allow
the new mysql_options() function to save options in the MYSQL
handler structure.
The mysqld variable key_buffer has changed names to
key_buffer_size, but you can still use the old name in your
startup files.
If you are running a version older than Version 3.20.28 and want to switch to Version 3.21, you need to do the following:
You can start the mysqld Version 3.21 server with safe_mysqld
--old-protocol to use it with clients from a Version 3.20 distribution.
In this case, the new client function mysql_errno() will not
return any server error, only CR_UNKNOWN_ERROR (but it
works for client errors), and the server uses the old password()
checking rather than the new one.
If you are NOT using the --old-protocol option to
mysqld, you will need to make the following changes:
scripts/add_long_password must be run to convert the
Password field in the mysql.user table to CHAR(16).
mysql.user table (to get 62-bit
rather than 31-bit passwords).
MySQL Version 3.20.28 and above can handle the new user table
format without affecting clients. If you have a MySQL version earlier
than Version 3.20.28, passwords will no longer work with it if you convert the
user table. So to be safe, you should first upgrade to at least Version
3.20.28 and then upgrade to Version 3.21.
The new client code works with a 3.20.x mysqld server, so
if you experience problems with 3.21.x, you can use the old 3.20.x server
without having to recompile the clients again.
If you are not using the --old-protocol option to mysqld,
old clients will issue the error message:
ERROR: Protocol mismatch. Server Version = 10 Client Version = 9
The new Perl DBI/DBD interface also supports the old
mysqlperl interface. The only change you have to make if you use
mysqlperl is to change the arguments to the connect() function.
The new arguments are: host, database, user,
password (the user and password arguments have changed
places).
See section 22.5.2 The DBI Interface.
The following changes may affect queries in old applications:
HAVING must now be specified before any ORDER BY clause.
LOCATE() have been swapped.
DATE,
TIME, and TIMESTAMP.
If you are using MySQL Version 3.23, you can copy the .frm,
.MYI, and .MYD files between different architectures that
support the same floating-point format. (MySQL takes care of any
byte swapping issues.)
The MySQL ISAM data and index files (`.ISD' and
`*.ISM', respectively) are architecture-dependent and in some cases
OS-dependent. If you want to move your applications to another machine
that has a different architecture or OS than your current machine, you
should not try to move a database by simply copying the files to the
other machine. Use mysqldump instead.
By default, mysqldump will create a file full of SQL statements.
You can then transfer the file to the other machine and feed it as input
to the mysql client.
Try mysqldump --help to see what options are available.
If you are moving the data to a newer version of MySQL, you should use
mysqldump --opt with the newer version to get a fast, compact dump.
The easiest (although not the fastest) way to move a database between two machines is to run the following commands on the machine on which the database is located:
shell> mysqladmin -h 'other hostname' create db_name
shell> mysqldump --opt db_name \
| mysql -h 'other hostname' db_name
If you want to copy a database from a remote machine over a slow network, you can use:
shell> mysqladmin create db_name
shell> mysqldump -h 'other hostname' --opt --compress db_name \
| mysql db_name
You can also store the result in a file, then transfer the file to the target machine and load the file into the database there. For example, you can dump a database to a file on the source machine like this:
shell> mysqldump --quick db_name | gzip > db_name.contents.gz
(The file created in this example is compressed.) Transfer the file containing the database contents to the target machine and run these commands there:
shell> mysqladmin create db_name shell> gunzip < db_name.contents.gz | mysql db_name
You can also use mysqldump and mysqlimport to accomplish
the database transfer.
For big tables, this is much faster than simply using mysqldump.
In the commands shown below, DUMPDIR represents the full pathname
of the directory you use to store the output from mysqldump.
First, create the directory for the output files and dump the database:
shell> mkdir DUMPDIR shell> mysqldump --tab=DUMPDIR db_name
Then transfer the files in the DUMPDIR directory to some corresponding
directory on the target machine and load the files into MySQL
there:
shell> mysqladmin create db_name # create database shell> cat DUMPDIR/*.sql | mysql db_name # create tables in database shell> mysqlimport db_name DUMPDIR/*.txt # load data into tables
Also, don't forget to copy the mysql database, because that's where the
grant tables (user, db, host) are stored. You may have
to run commands as the MySQL root user on the new machine
until you have the mysql database in place.
After you import the mysql database on the new machine, execute
mysqladmin flush-privileges so that the server reloads the grant table
information.
MySQL includes some extensions that you probably will not find in
other SQL databases. Be warned that if you use them, your code will not be
portable to other SQL servers. In some cases, you can write code that
includes MySQL extensions, but is still portable, by using comments
of the form /*! ... */. In this case, MySQL will parse and
execute the code within the comment as it would any other MySQL
statement, but other SQL servers will ignore the extensions. For example:
SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ...
If you add a version number after the '!', the syntax will only be
executed if the MySQL version is equal to or newer than the used
version number:
CREATE /*!32302 TEMPORARY */ TABLE (a int);
The above means that if you have Version 3.23.02 or newer, then MySQL
will use the TEMPORARY keyword.
MySQL extensions are listed below:
MEDIUMINT, SET, ENUM, and the
different BLOB and TEXT types.
AUTO_INCREMENT, BINARY, NULL,
UNSIGNED, and ZEROFILL.
BINARY attribute or use the BINARY cast, which causes
comparisons to be done according to the ASCII order used on the
MySQL server host.
db_name.tbl_name syntax. Some SQL servers provide
the same functionality but call this User space.
MySQL doesn't support tablespaces as in:
create table ralph.my_table...IN my_tablespace.
LIKE is allowed on numeric columns.
INTO OUTFILE and STRAIGHT_JOIN in a SELECT
statement. See section 7.19 SELECT Syntax.
SQL_SMALL_RESULT option in a SELECT statement.
EXPLAIN SELECT to get a description on how tables are joined.
INDEX or KEY in a CREATE TABLE
statement. See section 7.7 CREATE TABLE Syntax.
TEMPORARY or IF NOT EXISTS with CREATE TABLE.
COUNT(DISTINCT list) where 'list' is more than one element.
CHANGE col_name, DROP col_name, or DROP
INDEX, IGNORE or RENAME in an ALTER TABLE
statement. See section 7.8 ALTER TABLE Syntax.
RENAME TABLE. See section 7.9 RENAME TABLE Syntax.
ADD, ALTER, DROP, or CHANGE
clauses in an ALTER TABLE statement.
DROP TABLE with the keywords IF EXISTS.
DROP TABLE statement.
LIMIT clause of the DELETE statement.
DELAYED clause of the INSERT and REPLACE
statements.
LOW_PRIORITY clause of the INSERT, REPLACE,
DELETE, and UPDATE statements.
LOAD DATA INFILE. In many cases, this syntax is compatible with
Oracle's LOAD DATA INFILE. See section 7.23 LOAD DATA INFILE Syntax.
ANALYZE TABLE, CHECK TABLE, OPTIMIZE TABLE, and
REPAIR TABLE statements.
SHOW statement.
See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
SET OPTION statement. See section 7.33 SET Syntax.
GROUP BY part.
This gives better performance for some very specific, but quite normal
queries.
See section 7.4.13 Functions for Use with GROUP BY Clauses.
|| and && operators to mean
logical OR and AND, as in the C programming language. In MySQL,
|| and OR are synonyms, as are && and AND.
Because of this nice syntax, MySQL doesn't support
the ANSI SQL || operator for string concatenation; use
CONCAT() instead. Because CONCAT() takes any number
of arguments, it's easy to convert use of the || operator to
MySQL.
CREATE DATABASE or DROP DATABASE.
See section 7.5 CREATE DATABASE Syntax.
% operator is a synonym for MOD(). That is,
N % M is equivalent to MOD(N,M). % is supported
for C programmers and for compatibility with PostgreSQL.
=, <>, <= ,<, >=,>,
<<, >>, <=>, AND, OR, or LIKE
operators may be used in column comparisons to the left of the
FROM in SELECT statements. For example:
mysql> SELECT col1=1 AND col2=2 FROM tbl_name;
LAST_INSERT_ID() function.
See section 22.4.30 mysql_insert_id().
REGEXP and NOT REGEXP extended regular expression
operators.
CONCAT() or CHAR() with one argument or more than two
arguments. (In MySQL, these functions can take any number of
arguments.)
BIT_COUNT(), CASE, ELT(),
FROM_DAYS(), FORMAT(), IF(), PASSWORD(),
ENCRYPT(), md5(), ENCODE(), DECODE(),
PERIOD_ADD(), PERIOD_DIFF(), TO_DAYS(), or
WEEKDAY() functions.
TRIM() to trim substrings. ANSI SQL only supports removal
of single characters.
GROUP BY functions STD(), BIT_OR(), and
BIT_AND().
REPLACE instead of DELETE + INSERT.
See section 7.22 REPLACE Syntax.
FLUSH flush_option statement.
:=:
SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg FROM test_table; SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;
If you start mysqld with the --ansi option, the following behavior
of MySQL changes:
|| is string concatenation instead of OR.
REAL will be a synonym for FLOAT instead of a synonym of
DOUBLE.
We try to make MySQL follow the ANSI SQL standard and the ODBC SQL standard, but in some cases MySQL does some things differently:
-- is only a comment if followed by a white space. See section 5.4.7 `--' as the Start of a Comment.
VARCHAR columns, trailing spaces are removed when the value is
stored. See section F Known errors and design deficiencies in MySQL.
CHAR columns are silently changed to VARCHAR
columns. See section 7.7.1 Silent Column Specification Changes.
REVOKE to revoke privileges for
a table. See section 7.34 GRANT and REVOKE Syntax.
NULL AND FALSE will evaluate to NULL and not to FALSE.
This is because we don't think it's good to have to evaluate a lot of
extra conditions in this case.
The following functionality is missing in the current version of MySQL. For a prioritized list indicating when new extensions may be added to MySQL, you should consult the online MySQL TODO list. That is the latest version of the TODO list in this manual. See section G MySQL and the future (The TODO).
The following will not yet work in MySQL:
SELECT * FROM table1 WHERE id IN (SELECT id FROM table2); SELECT * FROM table1 WHERE id NOT IN (SELECT id FROM table2); SELECT * FROM table1 WHERE NOT EXISTS (SELECT id FROM table2 where table1.id=table2.id);
However, in many cases you can rewrite the query without a sub-select:
SELECT table1.* FROM table1,table2 WHERE table1.id=table2.id; SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.id=table2.id where table2.id IS NULL
For more complicated subqueries you can often create temporary tables
to hold the subquery. In some cases, however this option will not
work. The most frequently encountered of these cases arises with
DELETE statements, for which standard SQL does not support joins
(except in sub-selects). For this situation there are two options
available until subqueries are supported by MySQL.
The first option is to use a procedural programming language (such as
Perl or PHP) to submit a SELECT query to obtain the primary keys
for the records to be deleted, and then use these values to construct
the DELETE statement (DELETE FROM ... WHERE ... IN (key1,
key2, ...)).
The second option is to use interactive SQL to contruct a set of
DELETE statements automatically, using the MySQL
extension CONCAT() (in lieu of the standard || operator).
For example:
SELECT CONCAT('DELETE FROM tab1 WHERE pkid = ', tab1.pkid, ';')
FROM tab1, tab2
WHERE tab1.col1 = tab2.col2;
You can place this query in a script file and redirect input from it to
the mysql command-line interpreter, piping its output back to a
second instance of the interpreter:
prompt> mysql --skip-column-names mydb < myscript.sql | mysql mydb
MySQL only supports INSERT ... SELECT ... and
REPLACE ... SELECT ... Independent sub-selects will probably
be available in Version 4.0. You can now use the function IN() in
other contexts, however.
SELECT INTO TABLE
MySQL doesn't yet support the Oracle SQL extension:
SELECT ... INTO TABLE .... MySQL supports instead the
ANSI SQL syntax INSERT INTO ... SELECT ..., which is basically
the same thing.
Alternatively, you can use SELECT INTO OUTFILE... or CREATE
TABLE ... SELECT to solve your problem.
As MySQL does nowadays support transactions, the following
discussion is only valid if you are only using the non-transaction-safe
table types. See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax.
The question is often asked, by the curious and the critical, ``Why is MySQL not a transactional database?'' or ``Why does MySQL not support transactions?''
MySQL has made a conscious decision to support another paradigm for data integrity, ``atomic operations.'' It is our thinking and experience that atomic operations offer equal or even better integrity with much better performance. We, nonetheless, appreciate and understand the transactional database paradigm and plan, within the next few releases, to introduce transaction-safe tables on a per table basis. We will be giving our users the possibility to decide if they need the speed of atomic operations or if they need to use transactional features in their applications.
How does one use the features of MySQL to maintain rigorous integrity and how do these features compare with the transactional paradigm?
First, in the transactional paradigm, if your applications are written in a way that is dependent on the calling of ``rollback'' instead of ``commit'' in critical situations, then transactions are more convenient. Moreover, transactions ensure that unfinished updates or corrupting activities are not committed to the database; the server is given the opportunity to do an automatic rollback and your database is saved.
MySQL, in almost all cases, allows you to solve for potential problems by including simple checks before updates and by running simple scripts that check the databases for inconsistencies and automatically repair or warn if such occurs. Note that just by using the MySQL log or even adding one extra log, one can normally fix tables perfectly with no data integrity loss.
Moreover, fatal transactional updates can be rewritten to be
atomic. In fact,we will go so far as to say that all integrity problems
that transactions solve can be done with LOCK TABLES or atomic updates,
ensuring that you never will get an automatic abort from the database,
which is a common problem with transactional databases.
Not even transactions can prevent all loss if the server goes down. In such cases even a transactional system can lose data. The difference between different systems lies in just how small the time-lap is where they could lose data. No system is 100% secure, only ``secure enough.'' Even Oracle, reputed to be the safest of transactional databases, is reported to sometimes lose data in such situations.
To be safe with MySQL, you only need to have backups and have the update logging turned on. With this you can recover from any situation that you could with any transactional database. It is, of course, always good to have backups, independent of which database you use.
The transactional paradigm has its benefits and its drawbacks. Many users and application developers depend on the ease with which they can code around problems where an abort appears to be, or is necessary, and they may have to do a little more work with MySQL to either think differently or write more. If you are new to the atomic operations paradigm, or more familiar or more comfortable with transactions, do not jump to the conclusion that MySQL has not addressed these issues. Reliability and integrity are foremost in our minds. Recent estimates indicate that there are more than 1,000,000 mysqld servers currently running, many of which are in production environments. We hear very, very seldom from our users that they have lost any data, and in almost all of those cases user error is involved. This is, in our opinion, the best proof of MySQL's stability and reliability.
Lastly, in situations where integrity is of highest importance,
MySQL's current features allow for transaction-level or better
reliability and integrity. If you lock tables with LOCK TABLES, all
updates will stall until any integrity checks are made. If you only obtain
a read lock (as opposed to a write lock), then reads and inserts are
still allowed to happen. The new inserted records will not be seen by
any of the clients that have a READ lock until they release their read
locks. With INSERT DELAYED you can queue inserts into a local queue,
until the locks are released, without having the client wait for the insert
to complete.
``Atomic,'' in the sense that we mean it, is nothing magical. It only means
that you can be sure that while each specific update is running, no other
user can interfere with it, and there will never be an automatic
rollback (which can happen on transaction based systems if you are not
very careful). MySQL also guarantees that there will not be
any dirty reads. You can find some example of how to write atomic updates
in the commit-rollback section. See section 5.6 How to Cope Without COMMIT/ROLLBACK.
We have thought quite a bit about integrity and performance, and we believe that our atomic operations paradigm allows for both high reliability and extremely high performance, on the order of three to five times the speed of the fastest and most optimally tuned of transactional databases. We didn't leave out transactions because they are hard to do. The main reason we went with atomic operations as opposed to transactions is that by doing this we could apply many speed optimizations that would not otherwise have been possible.
Many of our users who have speed foremost in their minds are not at all
concerned about transactions. For them transactions are not an
issue. For those of our users who are concerned with or have wondered
about transactions vis-a-vis MySQL, there is a ``MySQL
way'' as we have outlined above. For those where safety is more important
than speed, we recommend them to use the BDB tables for all their
critical data. See section 8.5 BDB or Berkeley_db Tables.
One final note: We are currently working on a safe replication schema that we believe to be better than any commercial replication system we know of. This system will work most reliably under the atomic operations, non-transactional, paradigm. Stay tuned.
A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep reissuing the entire query but can refer to the stored procedure. This provides better performance because the query has to be parsed only once, and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server.
A trigger is a stored procedure that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that automatically deletes the corresponding customer from a customer table when all his transactions are deleted.
The planned update language will be able to handle stored procedures, but without triggers. Triggers usually slow down everything, even queries for which they are not needed.
To see when MySQL might get stored procedures, see section G MySQL and the future (The TODO).
Note that foreign keys in SQL are not used to join tables, but are used
mostly for checking referential integrity (foreign key constraints). If
you want to get results from multiple tables from a SELECT
statement, you do this by joining tables:
SELECT * from table1,table2 where table1.id = table2.id;
See section 7.20 JOIN Syntax. See section 9.3.6 Using Foreign Keys.
The FOREIGN KEY syntax in MySQL exists only for compatibility
with other SQL vendors' CREATE TABLE commands; it doesn't do
anything. The FOREIGN KEY syntax without ON DELETE ... is
mostly used for documentation purposes. Some ODBC applications may use this
to produce automatic WHERE clauses, but this is usually easy to
override. FOREIGN KEY is sometimes used as a constraint check, but
this check is unnecessary in practice if rows are inserted into the tables in
the right order. MySQL only supports these clauses because some
applications require them to exist (regardless of whether or not they
work).
In MySQL, you can work around the problem of ON DELETE
... not being implemented by adding the appropriate DELETE statement to
an application when you delete records from a table that has a foreign key.
In practice this is as quick (in some cases quicker) and much more portable
than using foreign keys.
In the near future we will extend the FOREIGN KEY implementation so
that at least the information will be saved in the table specification file
and may be retrieved by mysqldump and ODBC. At a later stage we will
implement the foreign key constraints for application that can't easily be
coded to avoid them.
There are so many problems with foreign key constraints that we don't know where to start:
INSERT and UPDATE
statements, and in this case almost all FOREIGN KEY constraint
checks are useless because you usually insert records in the right
tables in the right order, anyway.
FOREIGN KEY ... ON DELETE rules when
one codes an application. It's not unusual that one loses a lot of
important information just because a wrong or misused ON DELETE rule.
The only nice aspect of FOREIGN KEY is that it gives ODBC and some
other client programs the ability to see how a table is connected and to use
this to show connection diagrams and to help in building applicatons.
MySQL will soon store FOREIGN KEY definitions so that a
client can ask for and receive an answer about how the original
connection was made. The current `.frm' file format does not have
any place for it. At a later stage we will implement the foreign key
constraints for application that can't easily be coded to avoid them.
MySQL doesn't support views, but this is on the TODO.
Some other SQL databases use `--' to start comments. MySQL
has `#' as the start comment character, even if the mysql
command-line tool removes all lines that start with `--'.
You can also use the C comment style /* this is a comment */ with
MySQL.
See section 7.37 Comment Syntax.
MySQL Version 3.23.3 and above supports the `--' comment style
only if the comment is followed by a space. This is because this
degenerate comment style has caused many problems with automatically
generated SQL queries that have used something like the following code,
where we automatically insert the value of the payment for
!payment!:
UPDATE tbl_name SET credit=credit-!payment!
What do you think will happen when the value of payment is negative?
Because 1--1 is legal in SQL, we think it is terrible that
`--' means start comment.
In MySQL Version 3.23 you can, however, use:
1-- This is a comment
The following discussion only concerns you if you are running a MySQL version earlier than Version 3.23:
If you have a SQL program in a text file that contains `--' comments you should use:
shell> replace " --" " #" < text-file-with-funny-comments.sql \
| mysql database
instead of the usual:
shell> mysql database < text-file-with-funny-comments.sql
You can also edit the command file ``in place'' to change the `--' comments to `#' comments:
shell> replace " --" " #" -- text-file-with-funny-comments.sql
Change them back with this command:
shell> replace " #" " --" -- text-file-with-funny-comments.sql
Entry level SQL92. ODBC levels 0-2.
COMMIT/ROLLBACK
The following mostly applies only for ISAM, MyISAM, and
HEAP tables. If you only use transaction-safe tables (BDB
tables) in an a update, you can do COMMIT and ROLLBACK also
with MySQL. See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax.
The problem with handling COMMIT-ROLLBACK efficiently with
the above table types would require a completely different table layout
than MySQL uses today. The table type would also need extra
threads that do automatic cleanups on the tables, and the disk usage
would be much higher. This would make these table types about 2-4 times
slower than they are today.
For the moment, we prefer implementing the SQL server language (something
like stored procedures). With this you would very seldom really need
COMMIT-ROLLBACK. This would also give much better performance.
Loops that need transactions normally can be coded with the help of
LOCK TABLES, and you don't need cursors when you can update records
on the fly.
We at TcX had a greater need for a real fast database than a 100% general database. Whenever we find a way to implement these features without any speed loss, we will probably do it. For the moment, there are many more important things to do. Check the TODO for how we prioritize things at the moment. (Customers with higher levels of support can alter this, so things may be reprioritized.)
The current problem is actually ROLLBACK. Without
ROLLBACK, you can do any kind of COMMIT action with
LOCK TABLES. To support ROLLBACK with the above table
types, MySQL would have to be changed to store all old records
that were updated and revert everything back to the starting point if
ROLLBACK was issued. For simple cases, this isn't that hard to do
(the current isamlog could be used for this purpose), but it
would be much more difficult to implement ROLLBACK for
ALTER/DROP/CREATE TABLE.
To avoid using ROLLBACK, you can use the following strategy:
LOCK TABLES ... to lock all the tables you want to access.
UNLOCK TABLES to release your locks.
This is usually a much faster method than using transactions with possible
ROLLBACKs, although not always. The only situation this solution
doesn't handle is when someone kills the threads in the middle of an
update. In this case, all locks will be released but some of the updates may
not have been executed.
You can also use functions to update records in a single operation. You can get a very efficient application by using the following techniques:
For example, when we are doing updates to some customer information, we
update only the customer data that has changed and test only that none of
the changed data, or data that depend on the changed data, has changed
compared to the original row. The test for changed data is done with the
WHERE clause in the UPDATE statement. If the record wasn't
updated, we give the client a message: "Some of the data you have changed
have been changed by another user". Then we show the old row versus the new
row in a window, so the user can decide which version of the customer record
he should use.
This gives us something that is similar to column locking but is actually
even better, because we only update some of the columns, using values that
are relative to their current values. This means that typical UPDATE
statements look something like these:
UPDATE tablename SET pay_back=pay_back+'relative change';
UPDATE customer
SET
customer_date='current_date',
address='new address',
phone='new phone',
money_he_owes_us=money_he_owes_us+'new_money'
WHERE
customer_id=id AND address='old address' AND phone='old phone';
As you can see, this is very efficient and works even if another client has
changed the values in the pay_back or money_he_owes_us columns.
In many cases, users have wanted ROLLBACK and/or LOCK
TABLES for the purpose of managing unique identifiers for some tables. This
can be handled much more efficiently by using an AUTO_INCREMENT column
and either the SQL function LAST_INSERT_ID() or the C API function
mysql_insert_id(). See section 22.4.30 mysql_insert_id().
At MySQL AB, we have never had any need for row-level locking because we have always been able to code around it. Some cases really need row locking, but they are very few. If you want row-level locking, you can use a flag column in the table and do something like this:
UPDATE tbl_name SET row_flag=1 WHERE id=ID;
MySQL returns 1 for the number of affected rows if the row was
found and row_flag wasn't already 1 in the original row.
You can think of it as MySQL changed the above query to:
UPDATE tbl_name SET row_flag=1 WHERE id=ID and row_flag <> 1;
MySQL has an advanced but non-standard security/privilege system. This section describes how it works.
Anyone using MySQL on a computer connected to the Internet should read this section to avoid the most common security mistakes.
In discussing security, we emphasize the necessity of fully protecting the entire server host (not simply the MySQL server) against all types of applicable attacks: eavesdropping, altering, playback, and denial of service. We do not cover all aspects of availability and fault tolerance here.
MySQL uses Access Control Lists (ACLs) security for all connections, queries, and other operations that a user may attempt to perform. There is also some support for SSL-encrypted connections between MySQL clients and servers. Many of the concepts discussed here are not specific to MySQL at all; the same general ideas apply to almost all applications.
When running MySQL, follow these guidelines whenever possible:
GRANT and
REVOKE commands are used for restricting access to MySQL. Do
not grant any more privileges than necessary. Never grant privileges to all
hosts.
Checklist:
mysql -u root. If you are able to connect successfully to the
server without being asked for a password, you have problems. Any user (not
just root) can connect to your MySQL server with full privileges!
Review the MySQL installation instructions, paying particular
attention to the item about setting a root password.
SHOW GRANTS and check to see who has access to
what. Remove those privileges that are not necessary using the REVOKE
command.
MD5() or another one-way
hashing function.
nmap. MySQL uses port 3306 by default. This port should
be inaccessible from untrusted hosts. Another simple way to check whether or
not your MySQL port is open is to type telnet
server_host 3306 from some remote machine, where
server_host is the hostname of your MySQL
server. If you get a connection and some garbage characters, the port is
open, and should be closed on your firewall or router, unless you really
have a good reason to keep it open. If telnet just hangs,
everything is OK, the port is blocked.
; DROP
DATABASE mysql;''. This is an extreme example, but large security leaks
and data loss may occur as a result of hackers using similar techniques,
if you do not prepare for them.
Also remember to check numeric data. A common mistake is to protect only
strings. Sometimes people think that if a database contains only publicly
available data that it need not be protected. This is incorrect. At least
denial-of-service type attacks can be performed on such
databases. The simplest way to protect from this type of attack is to use
apostrophes around the numeric constants: SELECT * FROM table
WHERE ID='234' instead of SELECT * FROM table WHERE ID=234.
MySQL automatically converts this string to a number and
strips all non-numeric symbols from it.
Checklist:
%22 (`"'), %23
(`#'), and %27 (`'') in the URL.
addslashes() function.
mysql_escape() API call.
escape and quote modifiers for query streams.
quote() method.
tcpdump and strings utilities. For most cases,
you can check whether or not MySQL data streams are unencrypted
by issuing a command like the following:
shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings(This works under Linux and should work with small modifications under other systems). Warning: If you do not see data this doesn't always actually mean that it is encrypted. If you need high security, you should consult with a security expert.
When you connect to a MySQL server, you normally should use a password. The password is not transmitted in clear text over the connection, however the encryption algorithm is not very strong, and with some effort a clever attacker can crack the password if he is able to sniff the traffic between the client and the server. If the connection between the client and the server goes through an untrusted network, you should use an SSH tunnel to encrypt the communication.
All other information is transferred as text that can be read by anyone
who is able to watch the connection. If you are concerned about this,
you can use the compressed protocol (in MySQL Version 3.22 and above)
to make things much harder. To make things even more secure you should
use ssh (see http://www.cs.hut.fi/ssh). With this, you
can get an encrypted TCP/IP connection between a MySQL server
and a MySQL client.
To make a MySQL system secure, you should strongly consider the following suggestions:
mysql -u other_user db_name if
other_user has no password. It is common behavior with client/server
applications that the client may specify any user name. You can change the
password of all users by editing the mysql_install_db script before
you run it, or only the password for the MySQL root user like
this:
shell> mysql -u root mysql
mysql> UPDATE user SET Password=PASSWORD('new_password')
WHERE user='root';
mysql> FLUSH PRIVILEGES;
root user.
It is very dangerous as any user with FILE privileges will be able to
create files
as root (for example, ~root/.bashrc). To prevent this
mysqld will refuse to run as root unless it is specified
directly via --user=root option.
mysqld can be run as any user instead. You can also create a new
Unix user mysql to make everything even more secure. If you run
mysqld as another Unix user, you don't need to change the
root user name in the user table, because MySQL
user names have nothing to do with Unix user names. You can edit the
mysql.server script to start mysqld as another Unix user.
Normally this is done with the su command. For more details, see
section 20.10 How to Run MySQL As a Normal User.
root user in the mysql.server
script, make sure this script is readable only by root.
mysqld runs as is the only user with
read/write privileges in the database directories.
mysqld as root unless you really
need to. Consider creating a user named mysql for that purpose.
mysqladmin processlist shows the text of the currently executing
queries, so any user who is allowed to execute that command might be able to
see if another user issues an UPDATE user SET
password=PASSWORD('not_secure') query.
mysqld reserves an extra connection for users who have the
process privilege, so that a MySQL root user can log
in and check things even if all normal connections are in use.
mysqld daemon! To make this a bit safer, all files generated with
SELECT ... INTO OUTFILE are readable to everyone, and you can't
overwrite existing files.
The file privilege may also be used to read any file accessible
to the Unix user that the server runs as. This could be abused, for example,
by using LOAD DATA to load `/etc/passwd' into a table, which
can then be read with SELECT.
--secure option to
mysqld should make hostnames safe. In any case, you should be very
careful about creating grant table entries using hostname values that
contain wild cards!
The following mysqld options affect networking security:
--secure
gethostbyname() system call are
checked to make sure they resolve back to the original hostname. This
makes it harder for someone on the outside to get access by pretending
to be another host. This option also adds some sanity checks of
hostnames. The option is turned off by default in MySQL Version
3.21 because sometimes it takes a long time to perform backward resolutions.
MySQL Version 3.22 caches hostnames and has this option enabled by
default.
--skip-grant-tables
mysqladmin
flush-privileges or mysqladmin reload.)
--skip-name-resolve
Host column values in the grant
tables must be IP numbers or localhost.
--skip-networking
mysqld must be made via Unix sockets. This option is unsuitable for
systems that use MIT-pthreads, because the MIT-pthreads package doesn't
support Unix sockets.
The primary function of the MySQL privilege system is to authenticate a user connecting from a given host, and to associate that user with privileges on a database such as select, insert, update and delete.
Additional functionality includes the ability to have an anonymous user and
to grant privileges for MySQL-specific functions such as LOAD
DATA INFILE and administrative operations.
There are several distinctions between the way user names and passwords are used by MySQL and the way they are used by Unix or Windows:
-u or
--user options. This means that you can't make a database secure in
any way unless all MySQL user names have passwords. Anyone may
attempt to connect to the server using any name, and they will succeed if
they specify any name that doesn't have a password.
PASSWORD() and ENCRYPT() functions in section 7.4.12 Miscellaneous Functions. Note that even if the password is stored 'scrambled', and
knowing your 'scrambled' password is enough to be able to connect to
the MySQL server!
MySQL client programs generally require that you specify connection
parameters when you want to access a MySQL server: the host you want
to connect to, your user name, and your password. For example, the
mysql client can be started like this (optional arguments are enclosed
between `[' and `]'):
shell> mysql [-h host_name] [-u user_name] [-pyour_pass]
Alternate forms of the -h, -u, and -p options are
--host=host_name, --user=user_name, and
--password=your_pass. Note that there is no space between
-p or --password= and the password following it.
NOTE: Specifying a password on the command line is not secure!
Any user on your system may then find out your password by typing a command
like: ps auxww. See section 4.16.5 Option Files.
mysql uses default values for connection parameters that are missing
from the command line:
localhost.
-p is missing.
Thus, for a Unix user joe, the following commands are equivalent:
shell> mysql -h localhost -u joe shell> mysql -h localhost shell> mysql -u joe shell> mysql
Other MySQL clients behave similarly.
On Unix systems, you can specify different default values to be used when you make a connection, so that you need not enter them on the command line each time you invoke a client program. This can be done in a couple of ways:
[client] section of the
`.my.cnf' configuration file in your home directory. The relevant
section of the file might look like this:
[client] host=host_name user=user_name password=your_passSee section 4.16.5 Option Files.
mysql using MYSQL_HOST. The
MySQL user name can be specified using USER (this is for
Windows only). The password can be specified using MYSQL_PWD
(but this is insecure; see the next section). See section A Environment Variables.
It is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed below, along with an assessment of the risks of each method:
mysql.user table. Knowing
the encrypted password for a user makes it possible to login as this
user. The passwords are only scrambled so that one shouldn't be able to
see the real password you used (if you happen to use a similar password
with your other applications).
-pyour_pass or --password=your_pass option on the command
line. This is convenient but insecure, because your password becomes visible
to system status programs (such as ps) that may be invoked by other
users to display command lines. (MySQL clients typically overwrite
the command-line argument with zeroes during their initialization sequence,
but there is still a brief interval during which the value is visible.)
-p or --password option (with no your_pass value
specified). In this case, the client program solicits the password from
the terminal:
shell> mysql -u user_name -p Enter password: ********The `*' characters represent your password. It is more secure to enter your password this way than to specify it on the command line because it is not visible to other users. However, this method of entering a password is suitable only for programs that you run interactively. If you want to invoke a client from a script that runs non-interactively, there is no opportunity to enter the password from the terminal. On some systems, you may even find that the first line of your script is read and interpreted (incorrectly) as your password!
[client] section of the `.my.cnf' file in your
home directory:
[client] password=your_passIf you store your password in `.my.cnf', the file should not be group or world readable or writable. Make sure the file's access mode is
400
or 600.
See section 4.16.5 Option Files.
MYSQL_PWD environment variable, but
this method must be considered extremely insecure and should not be used.
Some versions of ps include an option to display the environment of
running processes; your password will be in plain sight for all to see if
you set MYSQL_PWD. Even on systems without such a version of
ps, it is unwise to assume there is no other method to observe process
environments. See section A Environment Variables.
All in all, the safest methods are to have the client program prompt for the password or to specify the password in a properly protected `.my.cnf' file.
Information about user privileges is stored in the user, db,
host, tables_priv, and columns_priv tables in the
mysql database (that is, in the database named mysql). The
MySQL server reads the contents of these tables when it starts up
and under the circumstances indicated in section 6.11 When Privilege Changes Take Effect.
The names used in this manual to refer to the privileges provided by MySQL are shown below, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies:
| Privilege | Column | Context |
| select | Select_priv | tables |
| insert | Insert_priv | tables |
| update | Update_priv | tables |
| delete | Delete_priv | tables |
| index | Index_priv | tables |
| alter | Alter_priv | tables |
| create | Create_priv | databases, tables, or indexes |
| drop | Drop_priv | databases or tables |
| grant | Grant_priv | databases or tables |
| references | References_priv | databases or tables |
| reload | Reload_priv | server administration |
| shutdown | Shutdown_priv | server administration |
| process | Process_priv | server administration |
| file | File_priv | file access on server |
The select, insert, update, and delete privileges allow you to perform operations on rows in existing tables in a database.
SELECT statements require the select privilege only if they
actually retrieve rows from a table. You can execute certain SELECT
statements even without permission to access any of the databases on the
server. For example, you could use the mysql client as a simple
calculator:
mysql> SELECT 1+1; mysql> SELECT PI()*2;
The index privilege allows you to create or drop (remove) indexes.
The alter privilege allows you to use ALTER TABLE.
The create and drop privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables.
Note that if you grant the drop privilege for the mysql
database to a user, that user can drop the database in which the
MySQL access privileges are stored!
The grant privilege allows you to give to other users those privileges you yourself possess.
The file privilege gives you permission to read and write files on
the server using the LOAD DATA INFILE and SELECT ... INTO
OUTFILE statements. Any user to whom this privilege is granted can read or
write any file that the MySQL server can read or write.
The remaining privileges are used for administrative operations, which are
performed using the mysqladmin program. The table below shows which
mysqladmin commands each administrative privilege allows you to
execute:
| Privilege | Commands permitted to privilege holders |
| reload | reload, refresh,
flush-privileges, flush-hosts, flush-logs, and
flush-tables
|
| shutdown | shutdown
|
| process | processlist, kill
|
The reload command tells the server to re-read the grant tables. The
refresh command flushes all tables and opens and closes the log
files. flush-privileges is a synonym for reload. The other
flush-* commands perform functions similar to refresh but are
more limited in scope, and may be preferable in some instances. For example,
if you want to flush just the log files, flush-logs is a better choice
than refresh.
The shutdown command shuts down the server.
The processlist command displays information about the threads
executing within the server. The kill command kills server threads.
You can always display or kill your own threads, but you need the
process privilege to display or kill threads initiated by other
users.
It is a good idea in general to grant privileges only to those users who need them, but you should exercise particular caution in granting certain privileges:
SELECT. This includes the contents of all databases
hosted by the server!
mysql database can be used to change passwords
and other access privilege information. (Passwords are stored
encrypted, so a malicious user cannot simply read them to know the plain
text password). If they can access the mysql.user password
column, they can use it to log into the MySQL server
for the given user. (With sufficient privileges, the same user can
replace a password with a different one.)
There are some things that you cannot do with the MySQL privilege system:
The MySQL privilege system ensures that all users may do exactly the things that they are supposed to be allowed to do. When you connect to a MySQL server, your identity is determined by the host from which you connect and the user name you specify. The system grants privileges according to your identity and what you want to do.
MySQL considers both your hostname and user name in identifying you
because there is little reason to assume that a given user name belongs to
the same person everywhere on the Internet. For example, the user
bill who connects from whitehouse.gov need not be the same
person as the user bill who connects from microsoft.com.
MySQL handles this by allowing you to distinguish users on different
hosts that happen to have the same name: you can grant bill one set
of privileges for connections from whitehouse.gov, and a different set
of privileges for connections from microsoft.com.
MySQL access control involves two stages:
The server uses the user, db, and host tables in the
mysql database at both stages of access control. The fields in these
grant tables are shown below:
| Table name | user | db | host
|
| Scope fields | Host | Host | Host
|
User | Db | Db
| |
Password | User | ||
| Privilege fields | Select_priv | Select_priv | Select_priv
|
Insert_priv | Insert_priv | Insert_priv
| |
Update_priv | Update_priv | Update_priv
| |
Delete_priv | Delete_priv | Delete_priv
| |
Index_priv | Index_priv | Index_priv
| |
Alter_priv | Alter_priv | Alter_priv
| |
Create_priv | Create_priv | Create_priv
| |
Drop_priv | Drop_priv | Drop_priv
| |
Grant_priv | Grant_priv | Grant_priv
| |
References_priv | |||
Reload_priv | |||
Shutdown_priv | |||
Process_priv | |||
File_priv |
For the second stage of access control (request verification), the server
may, if the request involves tables, additionally consult the
tables_priv and columns_priv tables. The fields in these
tables are shown below:
| Table name | tables_priv | columns_priv
|
| Scope fields | Host | Host
|
Db | Db
| |
User | User
| |
Table_name | Table_name
| |
Column_name
| ||
| Privilege fields | Table_priv | Column_priv
|
Column_priv | ||
| Other fields | Timestamp | Timestamp
|
Grantor |
Each grant table contains scope fields and privilege fields.
Scope fields determine the scope of each entry in the tables, that is, the
context in which the entry applies. For example, a user table entry
with Host and User values of 'thomas.loc.gov' and
'bob' would be used for authenticating connections made to the server
by bob from the host thomas.loc.gov. Similarly, a db
table entry with Host, User, and Db fields of
'thomas.loc.gov', 'bob' and 'reports' would be used when
bob connects from the host thomas.loc.gov to access the
reports database. The tables_priv and columns_priv
tables contain scope fields indicating tables or table/column combinations
to which each entry applies.
For access-checking purposes, comparisons of Host values are
case insensitive. User, Password, Db, and
Table_name values are case sensitive.
Column_name values are case insensitive in MySQL Version
3.22.12 or later.
Privilege fields indicate the privileges granted by a table entry, that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in section 6.10 Access Control, Stage 2: Request Verification.
Scope fields are strings, declared as shown below; the default value for each is the empty string:
| Field name | Type | |
Host | CHAR(60)
| |
User | CHAR(16)
| |
Password | CHAR(16)
| |
Db | CHAR(64) | (CHAR(60) for the
tables_priv and columns_priv tables)
|
Table_name | CHAR(60)
| |
Column_name | CHAR(60)
|
In the user, db and host tables,
all privilege fields are declared as ENUM('N','Y') -- each can have a
value of 'N' or 'Y', and the default value is 'N'.
In the tables_priv and columns_priv tables, the privilege
fields are declared as SET fields:
| Table name | Field name | Possible set elements |
tables_priv | Table_priv | 'Select', 'Insert',
'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter'
|
tables_priv | Column_priv | 'Select', 'Insert',
'Update', 'References'
|
columns_priv | Column_priv | 'Select', 'Insert',
'Update', 'References'
|
Briefly, the server uses the grant tables like this:
user table scope fields determine whether to allow or reject
incoming connections. For allowed connections, any privileges granted in
the user table indicate the user's global (superuser) privileges.
These privileges apply to all databases on the server.
db and host tables are used together:
db table scope fields determine which users can access which
databases from which hosts. The privilege fields determine which operations
are allowed.
host table is used as an extension of the db table when you
want a given db table entry to apply to several hosts. For example,
if you want a user to be able to use a database from several hosts in
your network, leave the Host value empty in the user's db table
entry, then populate the host table with an entry for each of those
hosts. This mechanism is described more detail in section 6.10 Access Control, Stage 2: Request Verification.
tables_priv and columns_priv tables are similar to
the db table, but are more fine-grained: they apply at the
table and column levels rather than at the database level.
Note that administrative privileges (reload, shutdown,
etc.) are specified only in the user table. This is because
administrative operations are operations on the server itself and are not
database-specific, so there is no reason to list such privileges in the
other grant tables. In fact, only the user table need
be consulted to determine whether or not you can perform an administrative
operation.
The file privilege is specified only in the user table, too.
It is not an administrative privilege as such, but your ability to read or
write files on the server host is independent of the database you are
accessing.
The mysqld server reads the contents of the grant tables once, when it
starts up. Changes to the grant tables take effect as indicated in
section 6.11 When Privilege Changes Take Effect.
When you modify the contents of the grant tables, it is a good idea to make
sure that your changes set up privileges the way you want. For help in
diagnosing problems, see section 6.15 Causes of Access denied Errors. For advice on security issues,
see section 6.2 How to Make MySQL Secure Against Crackers.
A useful
diagnostic tool is the mysqlaccess script, which Yves Carlier has
provided for the MySQL distribution. Invoke mysqlaccess with
the --help option to find out how it works.
Note that mysqlaccess checks access using only the user,
db and host tables. It does not check table- or column-level
privileges.
When you attempt to connect to a MySQL server, the server accepts or rejects the connection based on your identity and whether or not you can verify your identity by supplying the correct password. If not, the server denies access to you completely. Otherwise, the server accepts the connection, then enters Stage 2 and waits for requests.
Your identity is based on two pieces of information:
Identity checking is performed using the three user table scope fields
(Host, User, and Password). The server accepts the
connection only if a user table entry matches your hostname and user
name, and you supply the correct password.
Values in the user table scope fields may be specified as follows:
Host value may be a hostname or an IP number, or 'localhost'
to indicate the local host.
Host
field.
Host value of '%' matches any hostname. A blank Host
value is equivalent to '%'. Note that these values match any
host that can create a connection to your server!
Host values specified as IP numbers, you
can specify a netmask indicating how many address bits to use for the
network number. For example:
GRANT ALL PRIVILEGES on db.* to david@'192.58.197.0/255.255.255.0';This will allow everyone to connect from an IP where the following is true:
user_ip & netmask = host_ip.In the above example all IP:s in the interval 192.58.197.0 - 192.58.197.255 can connect to the MySQL server.
User field, but you can
specify a blank value, which matches any name. If the user table
entry that matches an incoming connection has a blank user name, the user is
considered to be the anonymous user (the user with no name), rather than the
name that the client actually specified. This means that a blank user name
is used for all further access checking for the duration of the connection
(that is, during Stage 2).
Password field can be blank. This does not mean that any password
matches, it means the user must connect without specifying a password.
Non-blank Password values represent encrypted passwords.
MySQL does not store passwords in plaintext form for anyone to
see. Rather, the password supplied by a user who is attempting to
connect is encrypted (using the PASSWORD() function). The
encrypted password is then used when the client/server is checking if
the password is correct (This is done without the encrypted password
ever traveling over the connection.) Note that from MySQL's
point of view the encrypted password is the REAL password, so you should
not give anyone access to it! In particular, don't give normal users
read access to the tables in the mysql database!
The examples below show how various combinations of Host and
User values in user table entries apply to incoming
connections:
Host value | User value | Connections matched by entry |
'thomas.loc.gov' | 'fred' | fred, connecting from thomas.loc.gov
|
'thomas.loc.gov' | '' | Any user, connecting from thomas.loc.gov
|
'%' | 'fred' | fred, connecting from any host
|
'%' | '' | Any user, connecting from any host |
'%.loc.gov' | 'fred' | fred, connecting from any host in the loc.gov domain
|
'x.y.%' | 'fred' | fred, connecting from x.y.net, x.y.com,x.y.edu, etc. (this is probably not useful)
|
'144.155.166.177' | 'fred' | fred, connecting from the host with IP address 144.155.166.177
|
'144.155.166.%' | 'fred' | fred, connecting from any host in the 144.155.166 class C subnet
|
'144.155.166.0/24' | 'fred' | Same as previous example |
Because you can use IP wild-card values in the Host field (for example,
'144.155.166.%' to match every host on a subnet), there is the
possibility that someone might try to exploit this capability by naming a
host 144.155.166.somewhere.com. To foil such attempts, MySQL
disallows matching on hostnames that start with digits and a dot. Thus, if
you have a host named something like 1.2.foo.com, its name will never
match the Host column of the grant tables. Only an IP number can
match an IP wild-card value.
An incoming connection may be matched by more than one entry in the
user table. For example, a connection from thomas.loc.gov by
fred would be matched by several of the entries just shown above. How
does the server choose which entry to use if more than one matches? The
server resolves this question by sorting the user table after reading
it at startup time, then looking through the entries in sorted order when a
user attempts to connect. The first matching entry is the one that is used.
user table sorting works as follows. Suppose the user table
looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | % | root | ... | % | jeffrey | ... | localhost | root | ... | localhost | | ... +-----------+----------+-
When the server reads in the table, it orders the entries with the
most-specific Host values first ('%' in the Host column
means ``any host'' and is least specific). Entries with the same Host
value are ordered with the most-specific User values first (a blank
User value means ``any user'' and is least specific). The resulting
sorted user table looks like this:
+-----------+----------+- | Host | User | ... +-----------+----------+- | localhost | root | ... | localhost | | ... | % | jeffrey | ... | % | root | ... +-----------+----------+-
When a connection is attempted, the server looks through the sorted entries
and uses the first match found. For a connection from localhost by
jeffrey, the entries with 'localhost' in the Host column
match first. Of those, the entry with the blank user name matches both the
connecting hostname and user name. (The '%'/'jeffrey' entry would
have matched, too, but it is not the first match in the table.)
Here is another example. Suppose the user table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | % | jeffrey | ... | thomas.loc.gov | | ... +----------------+----------+-
The sorted table looks like this:
+----------------+----------+- | Host | User | ... +----------------+----------+- | thomas.loc.gov | | ... | % | jeffrey | ... +----------------+----------+-
A connection from thomas.loc.gov by jeffrey is matched by the
first entry, whereas a connection from whitehouse.gov by
jeffrey is matched by the second.
A common misconception is to think that for a given user name, all entries
that explicitly name that user will be used first when the server attempts to
find a match for the connection. This is simply not true. The previous
example illustrates this, where a connection from thomas.loc.gov by
jeffrey is first matched not by the entry containing 'jeffrey'
as the User field value, but by the entry with no user name!
If you have problems connecting to the server, print out the user
table and sort it by hand to see where the first match is being made.
Once you establish a connection, the server enters Stage 2. For each request
that comes in on the connection, the server checks whether you have
sufficient privileges to perform it, based on the type of operation you wish
to perform. This is where the privilege fields in the grant tables come into
play. These privileges can come from any of the user, db,
host, tables_priv, or columns_priv tables. The grant
tables are manipulated with GRANT and REVOKE commands.
See section 7.34 GRANT and REVOKE Syntax. (You may find it helpful to refer to
section 6.8 How the Privilege System Works, which lists the fields present in each of the grant
tables.)
The user table grants privileges that are assigned to you on a global
basis and that apply no matter what the current database is. For example, if
the user table grants you the delete privilege, you can
delete rows from any database on the server host! In other words,
user table privileges are superuser privileges. It is wise to grant
privileges in the user table only to superusers such as server or
database administrators. For other users, you should leave the privileges
in the user table set to 'N' and grant privileges on a
database-specific basis only, using the db and host tables.
The db and host tables grant database-specific privileges.
Values in the scope fields may be specified as follows:
Host
and Db fields of either table.
'%' Host value in the db table means ``any host.'' A
blank Host value in the db table means ``consult the
host table for further information.''
'%' or blank Host value in the host table means ``any
host.''
'%' or blank Db value in either table means ``any database.''
User value in either table matches the anonymous user.
The db and host tables are read in and sorted when the server
starts up (at the same time that it reads the user table). The
db table is sorted on the Host, Db, and User scope
fields, and the host table is sorted on the Host and Db
scope fields. As with the user table, sorting puts the most-specific
values first and least-specific values last, and when the server looks for
matching entries, it uses the first match that it finds.
The tables_priv and columns_priv tables grant table- and
column-specific privileges. Values in the scope fields may be specified as
follows:
Host field of either table.
'%' or blank Host value in either table means ``any host.''
Db, Table_name and Column_name fields cannot contain
wild cards or be blank in either table.
The tables_priv and columns_priv tables are sorted on
the Host, Db, and User fields. This is similar to
db table sorting, although the sorting is simpler because
only the Host field may contain wild cards.
The request verification process is described below. (If you are familiar with the access-checking source code, you will notice that the description here differs slightly from the algorithm used in the code. The description is equivalent to what the code actually does; it differs only to make the explanation simpler.)
For administrative requests (shutdown, reload, etc.), the
server checks only the user table entry, because that is the only table
that specifies administrative privileges. Access is granted if the entry
allows the requested operation and denied otherwise. For example, if you
want to execute mysqladmin shutdown but your user table entry
doesn't grant the shutdown privilege to you, access is denied
without even checking the db or host tables. (They
contain no Shutdown_priv column, so there is no need to do so.)
For database-related requests (insert, update, etc.), the
server first checks the user's global (superuser) privileges by looking in
the user table entry. If the entry allows the requested operation,
access is granted. If the global privileges in the user table are
insufficient, the server determines the user's database-specific privileges
by checking the db and host tables:
db table for a match on the Host,
Db, and User fields. The Host and User fields are
matched to the connecting user's hostname and MySQL user name. The
Db field is matched to the database the user wants to access. If
there is no entry for the Host and User, access is denied.
db table entry and its Host field is
not blank, that entry defines the user's database-specific privileges.
db table entry's Host field is blank, it
signifies that the host table enumerates which hosts should be allowed
access to the database. In this case, a further lookup is done in the
host table to find a match on the Host and Db fields.
If no host table entry matches, access is denied. If there is a
match, the user's database-specific privileges are computed as the
intersection (not the union!) of the privileges in the db and
host table entries, that is, the privileges that are 'Y' in both
entries. (This way you can grant general privileges in the db table
entry and then selectively restrict them on a host-by-host basis using the
host table entries.)
After determining the database-specific privileges granted by the db
and host table entries, the server adds them to the global privileges
granted by the user table. If the result allows the requested
operation, access is granted. Otherwise, the server checks the user's
table and column privileges in the tables_priv and columns_priv
tables and adds those to the user's privileges. Access is allowed or denied
based on the result.
Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
It may not be apparent why, if the global user entry privileges are
initially found to be insufficient for the requested operation, the server
adds those privileges to the database-, table-, and column-specific privileges
later. The reason is that a request might require more than one type of
privilege. For example, if you execute an INSERT ... SELECT
statement, you need both insert and select privileges.
Your privileges might be such that the user table entry grants one
privilege and the db table entry grants the other. In this case, you
have the necessary privileges to perform the request, but the server cannot
tell that from either table by itself; the privileges granted by the entries
in both tables must be combined.
The host table can be used to maintain a list of secure servers.
At TcX, the host table contains a list of all machines on the local
network. These are granted all privileges.
You can also use the host table to indicate hosts that are not
secure. Suppose you have a machine public.your.domain that is located
in a public area that you do not consider secure. You can allow access to
all hosts on your network except that machine by using host table
entries
like this:
+--------------------+----+- | Host | Db | ... +--------------------+----+- | public.your.domain | % | ... (all privileges set to 'N') | %.your.domain | % | ... (all privileges set to 'Y') +--------------------+----+-
Naturally, you should always test your entries in the grant tables (for
example, using mysqlaccess) to make sure your access privileges are
actually set up the way you think they are.
When mysqld starts, all grant table contents are read into memory and
become effective at that point.
Modifications to the grant tables that you perform using GRANT,
REVOKE, or SET PASSWORD are noticed by the server immediately.
If you modify the grant tables manually (using INSERT, UPDATE,
etc.), you should execute a FLUSH PRIVILEGES statement or run
mysqladmin flush-privileges or mysqladmin reload to tell the
server to reload the grant tables. Otherwise your changes will have no
effect until you restart the server. If you change the grant tables manually
but forget to reload the privileges, you will be wondering why your changes
don't seem to make any difference!
When the server notices that the grant tables have been changed, existing client connections are affected as follows:
USE db_name
command.
Global privilege changes and password changes take effect the next time the client connects.
After installing MySQL, you set up the initial access privileges by
running scripts/mysql_install_db.
See section 4.7.1 Quick Installation Overview.
The mysql_install_db script starts up the mysqld
server, then initializes the grant tables to contain the following set
of privileges:
root user is created as a superuser who can do
anything. Connections must be made from the local host.
NOTE:
The initial root password is empty, so anyone can connect as root
without a password and be granted all privileges.
'test' or starting with 'test_'. Connections must be
made from the local host. This means any local user can connect without a
password and be treated as the anonymous user.
mysqladmin shutdown or mysqladmin processlist.
NOTE: The default privileges are different for Windows. See section 4.13.4 Running MySQL on Windows.
Because your installation is initially wide open, one of the first things you
should do is specify a password for the MySQL
root user. You can do this as follows (note that you specify the
password using the PASSWORD() function):
shell> mysql -u root mysql
mysql> UPDATE user SET Password=PASSWORD('new_password')
WHERE user='root';
mysql> FLUSH PRIVILEGES;
You can, in MySQL Version 3.22 and above, use the SET PASSWORD
statement:
shell> mysql -u root mysql
mysql> SET PASSWORD FOR root=PASSWORD('new_password');
Another way to set the password is by using the mysqladmin command:
shell> mysqladmin -u root password new_password
Only users with write/update access to the mysql database can change the
password for others users. All normal users (not anonymous ones) can only
change their own password with either of the above commands or with
SET PASSWORD=PASSWORD('new password').
Note that if you update the password in the user table directly using
the first method, you must tell the server to re-read the grant tables (with
FLUSH PRIVILEGES), because the change will go unnoticed otherwise.
Once the root password has been set, thereafter you must supply that
password when you connect to the server as root.
You may wish to leave the root password blank so that you don't need
to specify it while you perform additional setup or testing. However, be sure
to set it before using your installation for any real production work.
See the scripts/mysql_install_db script to see how it sets up
the default privileges. You can use this as a basis to see how to
add other users.
If you want the initial privileges to be different than those just described
above, you can modify mysql_install_db before you run it.
To re-create the grant tables completely, remove all the `.frm',
`.MYI', and `.MYD' files in the directory containing the
mysql database. (This is the directory named `mysql' under
the database directory, which is listed when you run mysqld
--help.) Then run the mysql_install_db script, possibly after
editing it first to have the privileges you want.
NOTE: For MySQL versions older than Version 3.22.10,
you should NOT delete the `.frm' files. If you accidentally do this,
you should copy them back from your MySQL distribution before
running mysql_install_db.
You can add users two different ways: by using GRANT statements
or by manipulating the MySQL grant tables directly. The
preferred method is to use GRANT statements, because they are
more concise and less error-prone.
The examples below show how to use the mysql client to set up new
users. These examples assume that privileges are set up according to the
defaults described in the previous section. This means that to make changes,
you must be on the same machine where mysqld is running, you must
connect as the MySQL root user, and the root user must
have the insert privilege for the mysql database and the
reload administrative privilege. Also, if you have changed the
root user password, you must specify it for the mysql commands
below.
You can add new users by issuing GRANT statements:
shell> mysql --user=root mysql
mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysql> GRANT ALL PRIVILEGES ON *.* TO monty@"%"
IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost;
mysql> GRANT USAGE ON *.* TO dummy@localhost;
These GRANT statements set up three new users:
monty
'some_pass' to do so. Note that we must issue
GRANT statements for both monty@localhost and
monty@"%". If we don't add the entry with localhost, the
anonymous user entry for localhost that is created by
mysql_install_db will take precedence when we connect from the local
host, because it has a more specific Host field value and thus comes
earlier in the user table sort order.
admin
localhost without a password and who is
granted the reload and process administrative privileges.
This allows the user to execute the mysqladmin reload,
mysqladmin refresh, and mysqladmin flush-* commands, as well as
mysqladmin processlist . No database-related privileges are granted.
(They can be granted later by issuing additional GRANT statements.)
dummy
'N' -- the USAGE privilege
type allows you to create a user with no privileges. It is assumed that you
will grant database-specific privileges later.
You can also add the same user access information directly by issuing
INSERT statements and then telling the server to reload the grant
tables:
shell> mysql --user=root mysql
mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y')
mysql> INSERT INTO user VALUES('%','monty',PASSWORD('some_pass'),
'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y')
mysql> INSERT INTO user SET Host='localhost',User='admin',
Reload_priv='Y', Process_priv='Y';
mysql> INSERT INTO user (Host,User,Password)
VALUES('localhost','dummy','');
mysql> FLUSH PRIVILEGES;
Depending on your MySQL version, you may have to use a different
number of 'Y' values above (versions prior to Version 3.22.11 had fewer
privilege columns). For the admin user, the more readable extended
INSERT syntax that is available starting with Version 3.22.11 is used.
Note that to set up a superuser, you need only create a user table
entry with the privilege fields set to 'Y'. No db or
host table entries are necessary.
The privilege columns in the user table were not set explicitly in the
last INSERT statement (for the dummy user), so those columns
are assigned the default value of 'N'. This is the same thing that
GRANT USAGE does.
The following example adds a user custom who can connect from hosts
localhost, server.domain, and whitehouse.gov. He wants
to access the bankaccount database only from localhost,
the expenses database only from whitehouse.gov, and
the customer database from all three hosts. He wants
to use the password stupid from all three hosts.
To set up this user's privileges using GRANT statements, run these
commands:
shell> mysql --user=root mysql
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON bankaccount.*
TO custom@localhost
IDENTIFIED BY 'stupid';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON expenses.*
TO custom@whitehouse.gov
IDENTIFIED BY 'stupid';
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
ON customer.*
TO custom@'%'
IDENTIFIED BY 'stupid';
To set up the user's privileges by modifying the grant tables directly,
run these commands (note the FLUSH PRIVILEGES at the end):
shell> mysql --user=root mysql
mysql> INSERT INTO user (Host,User,Password)
VALUES('localhost','custom',PASSWORD('stupid'));
mysql> INSERT INTO user (Host,User,Password)
VALUES('server.domain','custom',PASSWORD('stupid'));
mysql> INSERT INTO user (Host,User,Password)
VALUES('whitehouse.gov','custom',PASSWORD('stupid'));
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES
('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y');
mysql> INSERT INTO db
(Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
Create_priv,Drop_priv)
VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y');
mysql> FLUSH PRIVILEGES;
The first three INSERT statements add user table entries that
allow user custom to connect from the various hosts with the given
password, but grant no permissions to him (all privileges are set to the
default value of 'N'). The next three INSERT statements add
db table entries that grant privileges to custom for the
bankaccount, expenses, and customer databases, but only
when accessed from the proper hosts. As usual, when the grant tables are
modified directly, the server must be told to reload them (with
FLUSH PRIVILEGES) so that the privilege changes take effect.
If you want to give a specific user access from any machine in a given
domain, you can issue a GRANT statement like the following:
mysql> GRANT ...
ON *.*
TO myusername@"%.mydomainname.com"
IDENTIFIED BY 'mypassword';
To do the same thing by modifying the grant tables directly, do this:
mysql> INSERT INTO user VALUES ('%.mydomainname.com', 'myusername',
PASSWORD('mypassword'),...);
mysql> FLUSH PRIVILEGES;
You can also use xmysqladmin, mysql_webadmin, and even
xmysql to insert, change, and update values in the grant tables.
You can find these utilities in the
Contrib directory of the MySQL
Website.
In most cases you should use GRANT to set up your users/passwords,
so the following only applies for advanced users. See section 7.34 GRANT and REVOKE Syntax.
The examples in the preceding sections illustrate an important principle:
when you store a non-empty password using INSERT or UPDATE
statements, you must use the PASSWORD() function to encrypt it. This
is because the user table stores passwords in encrypted form, not as
plaintext. If you forget that fact, you are likely to attempt to set
passwords like this:
shell> mysql -u root mysql
mysql> INSERT INTO user (Host,User,Password)
VALUES('%','jeffrey','biscuit');
mysql> FLUSH PRIVILEGES;
The result is that the plaintext value 'biscuit' is stored as the
password in the user table. When the user jeffrey attempts to
connect to the server using this password, the mysql client encrypts
it with PASSWORD() and sends the result to the server. The server
compares the value in the user table (the encrypted value of
'biscuit') to the encrypted password (which is not
'biscuit'). The comparison fails and the server rejects the
connection:
shell> mysql -u jeffrey -pbiscuit test Access denied
Passwords must be encrypted when they are inserted in the user
table, so the INSERT statement should have been specified like this
instead:
mysql> INSERT INTO user (Host,User,Password)
VALUES('%','jeffrey',PASSWORD('biscuit'));
You must also use the PASSWORD() function when you use SET
PASSWORD statements:
mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');
If you set passwords using the GRANT ... IDENTIFIED BY statement
or the mysqladmin password command, the PASSWORD() function
is unnecessary. They both take care of encrypting the password for you,
so you would specify a password of 'biscuit' like this:
mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';
or
shell> mysqladmin -u jeffrey password biscuit
NOTE: PASSWORD() does not perform password encryption in the
same way that Unix passwords are encrypted. You should not assume that if
your Unix password and your MySQL password are the same, that
PASSWORD() will result in the same encrypted value as is stored in the
Unix password file. See section 6.4 MySQL User Names and Passwords.
Access denied Errors
If you encounter Access denied errors when you try to connect to the
MySQL server, the list below indicates some courses of
action you can take to correct the problem:
mysql_install_db
script to set up the initial grant table contents? If not, do so.
See section 6.12 Setting Up the Initial MySQL Privileges. Test the initial privileges by executing
this command:
shell> mysql -u root testThe server should let you connect without error. You should also make sure you have a file `user.MYD' in the MySQL database directory. Ordinarily, this is `PATH/var/mysql/user.MYD', where
PATH is the
pathname to the MySQL installation root.
shell> mysql -u root mysqlThe server should let you connect because the MySQL
root user
has no password initially. That is also a security risk, so setting the
root password is something you should do while you're setting up
your other MySQL users.
If you try to connect as root and get this error:
Access denied for user: '@unknown' to database mysqlthis means that you don't have an entry in the
user table with a
User column value of 'root' and that mysqld cannot
resolve the hostname for your client. In this case, you must restart the
server with the --skip-grant-tables option and edit your
`/etc/hosts' or `\windows\hosts' file to add an entry for your
host.
mysql_fix_privilege_tables script? If not, do so. The structure of
the grant tables changed with MySQL Version 3.22.11 when the
GRANT statement became functional.
PASSWORD() function if you set the password with the
INSERT, UPDATE, or SET PASSWORD statements. The
PASSWORD() function is unnecessary if you specify the password using
the GRANT ... INDENTIFIED BY statement or the mysqladmin
password command.
See section 6.14 Setting Up Passwords.
localhost is a synonym for your local hostname, and is also the
default host to which clients try to connect if you specify no host
explicitly. However, connections to localhost do not work if you are
running on a system that uses MIT-pthreads (localhost connections are
made using Unix sockets, which are not supported by MIT-pthreads). To avoid
this problem on such systems, you should use the --host option to name
the server host explicitly. This will make a TCP/IP connection to the
mysqld server. In this case, you must have your real hostname in
user table entries on the server host. (This is true even if you are
running a client program on the same host as the server.)
Access denied error when trying to connect to the
database with mysql -u user_name db_name, you may have a problem
with the user table. Check this by executing mysql -u root
mysql and issuing this SQL statement:
mysql> SELECT * FROM user;The result should include an entry with the
Host and User
columns matching your computer's hostname and your MySQL user name.
Access denied error message will tell you who you are trying
to log in as, the host from which you are trying to connect, and whether
or not you were using a password. Normally, you should have one entry in
the user table that exactly matches the hostname and user name
that were given in the error message. For example if you get an error
message that contains Using password: NO, this means that you
tried to login without an password.
user table that matches that host:
Host ... is not allowed to connect to this MySQL serverYou can fix this by using the command-line tool
mysql (on the
server host!) to add a row to the user, db, or host
table for the user/hostname combination from which you are trying to
connect and then execute mysqladmin flush-privileges. If you are
not running MySQL Version 3.22 and you don't know the IP number or
hostname of the machine from which you are connecting, you should put an
entry with '%' as the Host column value in the user
table and restart mysqld with the --log option on the
server machine. After trying to connect from the client machine, the
information in the MySQL log will indicate how you really did
connect. (Then replace the '%' in the user table entry
with the actual hostname that shows up in the log. Otherwise, you'll
have a system that is insecure.)
Another reason for this error on Linux is that you are using a binary
MySQL version that is compiled with a different glibc version
than the one you are using. In this case you should either upgrade your
OS/glibc or download the source MySQL version and compile this
yourself. A source RPM is normally trivial to compile and install, so
this isn't a big problem.
shell> mysqladmin -u root -pxxxx -h some-hostname ver Access denied for user: 'root' (Using password: YES)This means that MySQL got some error when trying to resolve the IP to a hostname. In this case you can execute
mysqladmin
flush-hosts to reset the internal DNS cache. Some permanent solutions
are:
--skip-name-resolve.
--skip-host-cache.
localhost if you are running the server and the client
on the same machine.
/etc/hosts.
mysql -u root test works but mysql -h your_hostname -u root
test results in Access denied, then you may not have the correct name
for your host in the user table. A common problem here is that the
Host value in the user table entry specifies an unqualified hostname,
but your system's name resolution routines return a fully qualified domain
name (or vice-versa). For example, if you have an entry with host
'tcx' in the user table, but your DNS tells MySQL that
your hostname is 'tcx.subnet.se', the entry will not work. Try adding
an entry to the user table that contains the IP number of your host as
the Host column value. (Alternatively, you could add an entry to the
user table with a Host value that contains a wild card--for
example, 'tcx.%'. However, use of hostnames ending with `%' is
insecure and is not recommended!)
mysql -u user_name test works but mysql -u user_name
other_db_name doesn't work, you don't have an entry for other_db_name
listed in the db table.
mysql -u user_name db_name works when executed on the server
machine, but mysql -u host_name -u user_name db_name doesn't work when
executed on another client machine, you don't have the client machine listed
in the user table or the db table.
Access denied, remove from the
user table all entries that have Host values containing
wild cards (entries that contain `%' or `_'). A very common error
is to insert a new entry with Host='%' and
User='some user', thinking that this will allow you to specify
localhost to connect from the same machine. The reason that this
doesn't work is that the default privileges include an entry with
Host='localhost' and User=''. Because that entry
has a Host value 'localhost' that is more specific than
'%', it is used in preference to the new entry when connecting from
localhost! The correct procedure is to insert a second entry with
Host='localhost' and User='some_user', or to
remove the entry with Host='localhost' and
User=''.
db or
host table:
Access to database deniedIf the entry selected from the
db table has an empty value in the
Host column, make sure there are one or more corresponding entries in
the host table specifying which hosts the db table entry
applies to.
If you get the error when using the SQL commands SELECT ...
INTO OUTFILE or LOAD DATA INFILE, your entry in the user table
probably doesn't have the file privilege enabled.
Access denied when you run a client without any options, make
sure you haven't specified an old password in any of your option files!
See section 4.16.5 Option Files.
INSERT or
UPDATE statement) and your changes seem to be ignored, remember
that you must issue a FLUSH PRIVILEGES statement or execute a
mysqladmin flush-privileges command to cause the server to re-read
the privilege tables. Otherwise your changes have no effect until the
next time the server is restarted. Remember that after you set the
root password with an UPDATE command, you won't need to
specify it until after you flush the privileges, because the server
won't know you've changed the password yet!
mysql -u user_name db_name or mysql
-u user_name -pyour_pass db_name. If you are able to connect using the
mysql client, there is a problem with your program and not with the
access privileges. (Note that there is no space between -p and the
password; you can also use the --password=your_pass syntax to specify
the password. If you use the -p option alone, MySQL will prompt you
for the password.)
mysqld daemon with the
--skip-grant-tables option. Then you can change the MySQL
grant tables and use the mysqlaccess script to check whether or not
your modifications have the desired effect. When you are satisfied with your
changes, execute mysqladmin flush-privileges to tell the mysqld
server to start using the new grant tables. Note: Reloading the
grant tables overrides the --skip-grant-tables option. This allows
you to tell the server to begin using the grant tables again without bringing
it down and restarting it.
mysqld daemon with a debugging
option (for example, --debug=d,general,query). This will print host and
user information about attempted connections, as well as information about
each command issued. See section H.1 Debugging a MySQL server.
mysqldump mysql command. As always, post your problem using
the mysqlbug script. See section 2.3 How to Report Bugs or Problems. In some cases you may need
to restart mysqld with --skip-grant-tables to run
mysqldump.
A string is a sequence of characters, surrounded by either single quote (`'') or double quote (`"') characters (only the single quote if you run in ANSI mode). Examples:
'a string' "another string"
Within a string, certain sequences have special meaning. Each of these sequences begins with a backslash (`\'), known as the escape character. MySQL recognizes the following escape sequences:
\0
NUL) character.
\n
\t
\r
\b
\'
\"
\\
\%
\_
Note that if you use `\%' or `\_' in some string contexts, these will return the strings `\%' and `\_' and not `%' and `_'.
There are several ways to include quotes within a string:
The SELECT statements shown below demonstrate how quoting and
escaping work:
mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello'; +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello"; +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "This\nIs\nFour\nlines"; +--------------------+ | This Is Four lines | +--------------------+
If you want to insert binary data into a BLOB column, the following
characters must be represented by escape sequences:
NUL
\
'
"
If you write C code, you can use the C API function
mysql_escape_string() to escape characters for the INSERT
statement. See section 22.3 C API Function Overview. In Perl, you can use the
quote method of the DBI package to convert special
characters to the proper escape sequences. See section 22.5.2 The DBI Interface.
You should use an escape function on any string that might contain any of the special characters listed above!
Integers are represented as a sequence of digits. Floats use `.' as a decimal separator. Either type of number may be preceded by `-' to indicate a negative value.
Examples of valid integers:
1221 0 -32
Examples of valid floating-point numbers:
294.42 -32032.6809e+10 148.00
An integer may be used in a floating-point context; it is interpreted as the equivalent floating-point number.
MySQL supports hexadecimal values. In number context these act like an integer (64-bit precision). In string context these act like a binary string where each pair of hex digits is converted to a character:
mysql> SELECT 0xa+0
-> 10
mysql> select 0x5061756c;
-> Paul
Hexadecimal strings are often used by ODBC to give values for BLOB columns.
NULL Values
The NULL value means ``no data'' and is different from values such
as 0 for numeric types or the empty string for string types.
See section 20.17 Problems with NULL Values.
NULL may be represented by \N when using the text file import
or export formats (LOAD DATA INFILE, SELECT ... INTO OUTFILE).
See section 7.23 LOAD DATA INFILE Syntax.
Database, table, index, column, and alias names all follow the same rules in MySQL.
Note that the rules changed starting with MySQL Version 3.23.6 when we introduced quoting of identifiers (database, table, and column names) with ``'. `"' will also work to quote identifiers if you run in ANSI mode. See section 5.2 Running MySQL in ANSI Mode.
| Identifier | Max length | Allowed characters |
| Database | 64 | Any character that is allowed in a directory name except `/'. |
| Table | 64 | Any character that is allowed in a file name, except `/' or `.'. |
| Column | 64 | All characters. |
| Alias | 255 | All characters. |
Note that in addition to the above, you can't have ASCII(0) or ASCII(255) in an identifier.
Note that if the identifer is a restricted word or contains special characters
you must always quote it with ` when you use it:
SELECT * from `select` where `select`.id > 100;
In previous versions of MySQL, the name rules are as follows:
--default-character-set option
to mysqld.
See section 10.1.1 The Character Set Used for Data and Sorting.
It is recommended that you do not use names like 1e, because
an expression like 1e+1 is ambiguous. It may be interpreted as the
expression 1e + 1 or as the number 1e+1.
In MySQL you can refer to a column using any of the following forms:
| Column reference | Meaning |
col_name | Column col_name
from whichever table used in the query contains a column of that name.
|
tbl_name.col_name | Column col_name from table
tbl_name of the current database.
|
db_name.tbl_name.col_name | Column col_name from table
tbl_name of the database db_name. This form is available in
MySQL Version 3.22 or later.
|
`column_name` | A column that is a keyword or contains special characters. |
You need not specify a tbl_name or db_name.tbl_name prefix for
a column reference in a statement unless the reference would be ambiguous.
For example, suppose tables t1 and t2 each contain a column
c, and you retrieve c in a SELECT statement that uses
both t1 and t2. In this case, c is ambiguous because it
is not unique among the tables used in the statement, so you must indicate
which table you mean by writing t1.c or t2.c. Similarly, if
you are retrieving from a table t in database db1 and from a
table t in database db2, you must refer to columns in those
tables as db1.t.col_name and db2.t.col_name.
The syntax .tbl_name means the table tbl_name in the current
database. This syntax is accepted for ODBC compatibility, because some ODBC
programs prefix table names with a `.' character.
In MySQL, databases and tables correspond to directories and files within those directories. Consequently, the case sensitivity of the underlying operating system determines the case sensitivity of database and table names. This means database and table names are case sensitive in Unix and case insensitive in Windows.
NOTE: Although database and table names are case insensitive for
Windows, you should not refer to a given database or table using different
cases within the same query. The following query would not work because it
refers to a table both as my_table and as MY_TABLE:
mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1;
Column names are case insensitive in all cases.
Aliases on tables are case sensitive. The following query would not work
because it refers to the alias both as a and as A:
mysql> SELECT col_name FROM tbl_name AS a
WHERE a.col_name = 1 OR A.col_name = 2;
Aliases on columns are case insensitive.
MySQL supports thread-specific variables with the
@variablename syntax. A variable name may consist of
alphanumeric characters from the current character set and also
`_', `$', and `.' . The default character set is
ISO-8859-1 Latin1; this may be changed with the
--default-character-set option to mysqld. See section 10.1.1 The Character Set Used for Data and Sorting.
Variables don't have to be initialized. They contain NULL by default
and can store an integer, real, or string value. All variables for
a thread are automatically freed when the thread exits.
You can set a variable with the SET syntax:
SET @variable= { integer expression | real expression | string expression }
[,@variable= ...].
You can also set a variable in an expression with the @variable:=expr
syntax:
select @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3; +----------------------+------+------+------+ | @t1:=(@t2:=1)+@t3:=4 | @t1 | @t2 | @t3 | +----------------------+------+------+------+ | 5 | 5 | 1 | 4 | +----------------------+------+------+------+
(We had to use the := syntax here, because = was reserved for
comparisons.)
User variables may be used where expressions are allowed. Note that
this does not currently include use in contexts where a number is explicitly
required, such as in the LIMIT clause of a SELECT statement,
or the IGNORE number LINES clause of a LOAD DATA statement.
NOTE: In a SELECT statement, each expression is only
evaluated when it's sent to the client. This means that in the HAVING,
GROUP BY, or ORDER BY clause, you can't refer to an expression
that involves variables that are set in the SELECT part. For example,
the following statement will NOT work as expected:
SELECT (@aa:=id) AS a, (@aa+3) AS b FROM table_name HAVING b=5;
The reason is that @aa will not contain the value of the current
row, but the value of id for the previous accepted row.
MySQL supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available and summarizes the storage requirements for each column type, then provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values.
The column types supported by MySQL are listed below. The following code letters are used in the descriptions:
M
D
M-2.
Square brackets (`[' and `]') indicate parts of type specifiers that are optional.
Note that if you specify ZEROFILL for a column, MySQL will
automatically add the UNSIGNED attribute to the column.
TINYINT[(M)] [UNSIGNED] [ZEROFILL]
-128 to 127. The
unsigned range is 0 to 255.
SMALLINT[(M)] [UNSIGNED] [ZEROFILL]
-32768 to 32767. The
unsigned range is 0 to 65535.
MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]
-8388608 to
8388607. The unsigned range is 0 to 16777215.
INT[(M)] [UNSIGNED] [ZEROFILL]
-2147483648 to
2147483647. The unsigned range is 0 to 4294967295.
INTEGER[(M)] [UNSIGNED] [ZEROFILL]
INT.
BIGINT[(M)] [UNSIGNED] [ZEROFILL]
-9223372036854775808 to
9223372036854775807. The unsigned range is 0 to
18446744073709551615. Note that all arithmetic is done using
signed BIGINT or DOUBLE values, so you shouldn't use
unsigned big integers larger than 9223372036854775807 (63 bits)
except with bit functions! Note that `-', `+', and `*'
will use BIGINT arithmetic when both arguments are INTEGER
values! This means that if you multiply two big integers (or results
from functions that return integers) you may get unexpected results if
the result is larger than 9223372036854775807.
FLOAT(precision) [ZEROFILL]
precision can be
<=24 for a single-precision floating-point number and between 25
and 53 for a double-precision floating-point number. These types are like
the FLOAT and DOUBLE types described immediately below.
FLOAT(X) has the same range as the corresponding FLOAT and
DOUBLE types, but the display size and number of decimals is undefined.
In MySQL Version 3.23, this is a true floating-point value. In
earlier MySQL versions, FLOAT(precision) always has 2 decimals.
This syntax is provided for ODBC compatibility.
FLOAT[(M,D)] [ZEROFILL]
-3.402823466E+38 to
-1.175494351E-38, 0, and 1.175494351E-38 to
3.402823466E+38. The M is the display width and D is the
number of decimals. FLOAT without an argument or with an argument of
<= 24 stands for a single-precision floating-point number.
DOUBLE[(M,D)] [ZEROFILL]
-1.7976931348623157E+308 to
-2.2250738585072014E-308, 0, and
2.2250738585072014E-308 to 1.7976931348623157E+308. The M
is the display width and D is the number of decimals. DOUBLE
without an argument or FLOAT(X) where 25 <= X <= 53 stands for a
double-precision floating-point number.
DOUBLE PRECISION[(M,D)] [ZEROFILL]
REAL[(M,D)] [ZEROFILL]
DOUBLE.
DECIMAL[(M[,D])] [ZEROFILL]
CHAR column: ``unpacked'' means the number is stored as a string,
using one character for each digit of the value. The decimal point
and, for negative numbers, the `-' sign, are not counted in M. If
D is 0, values will have no decimal point or fractional part.
The maximum range of DECIMAL values is the same as for
DOUBLE, but the actual range for a given DECIMAL column
may be constrained by the choice of M and D.
If D is left out it's set to 0. If M is left out it's set to 10.
Note that in MySQL Version 3.22 the M argument includes the
sign and the decimal point.
NUMERIC(M,D) [ZEROFILL]
DECIMAL.
DATE
'1000-01-01' to '9999-12-31'.
MySQL displays DATE values in 'YYYY-MM-DD' format, but
allows you to assign values to DATE columns using either strings or
numbers.
DATETIME
'1000-01-01
00:00:00' to '9999-12-31 23:59:59'. MySQL displays
DATETIME values in 'YYYY-MM-DD HH:MM:SS' format, but allows you
to assign values to DATETIME columns using either strings or numbers.
TIMESTAMP[(M)]
'1970-01-01 00:00:00' to sometime in the
year 2037. MySQL displays TIMESTAMP values in
YYYYMMDDHHMMSS, YYMMDDHHMMSS, YYYYMMDD, or YYMMDD
format, depending on whether M is 14 (or missing), 12,
8, or 6, but allows you to assign values to TIMESTAMP
columns using either strings or numbers. A TIMESTAMP column is useful
for recording the date and time of an INSERT or UPDATE
operation because it is automatically set to the date and time of the most
recent operation if you don't give it a value yourself. You can also set it
to the current date and time by assigning it a NULL value. See section 7.3.6 Date and Time Types.
A TIMESTAMP is always stored in 4 bytes. The M argument only
affects how the TIMESTAMP column is displayed.
Note that TIMESTAMP(X) columns where X is 8 or 14 are reported to
be numbers while other TIMESTAMP(X) columns are reported to be
strings. This is just to ensure that one can reliably dump and restore
the table with these types!
TIME
'-838:59:59' to '838:59:59'.
MySQL displays TIME values in 'HH:MM:SS' format, but
allows you to assign values to TIME columns using either strings or
numbers.
YEAR[(2|4)]
1901 to 2155, 0000 in the 4-digit year format,
and 1970-2069 if you use the 2-digit format (70-69). MySQL displays
YEAR values in YYYY format, but allows you to assign values to
YEAR columns using either strings or numbers. (The YEAR type is
new in MySQL Version 3.22.)
[NATIONAL] CHAR(M) [BINARY]
M is 1 to 255 characters.
Trailing spaces are removed when the value is retrieved. CHAR values
are sorted and compared in case-insensitive fashion according to the
default character set unless the BINARY keyword is given.
NATIONAL CHAR (short form NCHAR) is the ANSI SQL way to
define that a CHAR column should use the default CHARACTER set. This is
the default in MySQL.
CHAR is a shorthand for CHARACTER.
MySQL allows you to create a column of type
CHAR(0). This is mainly useful when you have to be compliant with
some old applications that depend on the existence of a column but that do not
actually use the value. This is also quite nice when you need a
column that only can take 2 values: A CHAR(0), that is not defined
as NOT NULL, will only occupy one bit and can only take 2 values:
NULL or "".
[NATIONAL] VARCHAR(M) [BINARY]
M is 1 to 255 characters. VARCHAR values are sorted and
compared in case-insensitive fashion unless the BINARY keyword is
given. See section 7.7.1 Silent Column Specification Changes.
VARCHAR is a shorthand for CHARACTER VARYING.
TINYBLOB
TINYTEXT
BLOB or TEXT column with a maximum length of 255 (2^8 - 1)
characters. See section 7.7.1 Silent Column Specification Changes.
BLOB
TEXT
BLOB or TEXT column with a maximum length of 65535 (2^16 - 1)
characters. See section 7.7.1 Silent Column Specification Changes.
MEDIUMBLOB
MEDIUMTEXT
BLOB or TEXT column with a maximum length of 16777215
(2^24 - 1) characters. See section 7.7.1 Silent Column Specification Changes.
LONGBLOB
LONGTEXT
BLOB or TEXT column with a maximum length of 4294967295
(2^32 - 1) characters. See section 7.7.1 Silent Column Specification Changes. Note that because
the server/client protocol and MyISAM tables has currently a limit of
16M per communication packet / table row, you can't yet use this
the whole range of this type.
ENUM('value1','value2',...)
'value1', 'value2', ..., or NULL. An ENUM
can have a maximum of 65535 distinct values.
SET('value1','value2',...)
'value1', 'value2',
... A SET can have a maximum of 64 members.
The storage requirements for each of the column types supported by MySQL are listed below by category.
7.3.2 Numeric types
| Column type | Storage required |
TINYINT | 1 byte |
SMALLINT | 2 bytes |
MEDIUMINT | 3 bytes |
INT | 4 bytes |
INTEGER | 4 bytes |
BIGINT | 8 bytes |
FLOAT(X) | 4 if X <= 24 or 8 if 25 <= X <= 53 |
FLOAT | 4 bytes |
DOUBLE | 8 bytes |
DOUBLE PRECISION | 8 bytes |
REAL | 8 bytes |
DECIMAL(M,D) | M bytes (D+2, if M < D)
|
NUMERIC(M,D) | M bytes (D+2, if M < D)
|
7.3.3 Date and time types
| Column type | Storage required |
DATE | 3 bytes |
DATETIME | 8 bytes |
TIMESTAMP | 4 bytes |
TIME | 3 bytes |
YEAR | 1 byte |
| Column type | Storage required |
CHAR(M) | M bytes, 1 <= M <= 255
|
VARCHAR(M) | L+1 bytes, where L <= M and
1 <= M <= 255
|
TINYBLOB, TINYTEXT | L+1 bytes,
where L < 2^8
|
BLOB, TEXT | L+2 bytes,
where L < 2^16
|
MEDIUMBLOB, MEDIUMTEXT | L+3 bytes,
where L < 2^24
|
LONGBLOB, LONGTEXT | L+4 bytes,
where L < 2^32
|
ENUM('value1','value2',...) | 1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) |
SET('value1','value2',...) | 1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) |
VARCHAR and the BLOB and TEXT types are variable-length
types, for which the storage requirements depend on the actual length of
column values (represented by L in the preceding table), rather than
on the type's maximum possible size. For example, a VARCHAR(10)
column can hold a string with a maximum length of 10 characters. The actual
storage required is the length of the string (L), plus 1 byte to
record the length of the string. For the string 'abcd', L is 4
and the storage requirement is 5 bytes.
The BLOB and TEXT types require 1, 2, 3, or 4 bytes to record
the length of the column value, depending on the maximum possible length of
the type.
If a table includes any variable-length column types, the record format will also be variable-length. Note that when a table is created, MySQL may, under certain conditions, change a column from a variable-length type to a fixed-length type, or vice-versa. See section 7.7.1 Silent Column Specification Changes.
The size of an ENUM object is determined by the number of different
enumeration values. One byte is used for enumerations with up to 255 possible
values. Two bytes are used for enumerations with up to 65535 values.
The size of a SET object is determined by the number of different
set members. If the set size is N, the object occupies (N+7)/8
bytes, rounded up to 1, 2, 3, 4, or 8 bytes. A SET can have a maximum
of 64 members.
MySQL supports all of the ANSI/ISO SQL92 numeric types. These
types include the exact numeric data types (NUMERIC,
DECIMAL, INTEGER, and SMALLINT), as well as the
approximate numeric data types (FLOAT, REAL, and
DOUBLE PRECISION). The keyword INT is a synonym for
INTEGER, and the keyword DEC is a synonym for
DECIMAL.
The NUMERIC and DECIMAL types are implemented as the same
type by MySQL, as permitted by the SQL92 standard. They are
used for values for which it is important to preserve exact precision,
for example with monetary data. When declaring a column of one of these
types the precision and scale can be (and usually is) specified; for
example:
salary DECIMAL(9,2)
In this example, 9 (precision) represents the number of
significant decimal digits that will be stored for values, and
2 (scale) represents the number of digits that will be
stored following the decimal point. In this case, therefore, the range
of values that can be stored in the salary column is from
-9999999.99 to 9999999.99. In ANSI/ISO SQL92, the syntax
DECIMAL(p) is equivalent to DECIMAL(p,0). Similarly, the
syntax DECIMAL is equivalent to DECIMAL(p,0), where the
implementation is allowed to decide the value of p.
MySQL does not currently support either of these variant forms
of the DECIMAL/NUMERIC data types. This is not generally
a serious problem, as the principal benefits of these types derive from
the ability to control both precision and scale explicitly.
DECIMAL and NUMERIC values are stored as strings, rather
than as binary floating-point numbers, in order to preserve the decimal
precision of those values. One character is used for each digit of the
value, the decimal point (if scale > 0), and the `-' sign
(for negative numbers). If scale is 0, DECIMAL and
NUMERIC values contain no decimal point or fractional part.
The maximum range of DECIMAL and NUMERIC values is the
same as for DOUBLE, but the actual range for a given
DECIMAL or NUMERIC column can be constrained by the
precision or scale for a given column. When such a column
is assigned a value with more digits following the decimal point than
are allowed by the specified scale, the value is rounded to that
scale. When a DECIMAL or NUMERIC column is
assigned a value whose magnitude exceeds the range implied by the
specified (or defaulted) precision and scale,
MySQL stores the value representing the corresponding end
point of that range.
As an extension to the ANSI/ISO SQL92 standard, MySQL also
supports the integral types TINYINT, MEDIUMINT, and
BIGINT as listed in the tables above. Another extension is
supported by MySQL for optionally specifying the display width
of an integral value in parentheses following the base keyword for the
type (for example, INT(4)). This optional width specification is
used to left-pad the display of values whose width is less than the
width specified for the column, but does not constrain the range of
values that can be stored in the column, nor the number of digits that
will be displayed for values whose width exceeds that specified for the
column. When used in conjunction with the optional extension attribute
ZEROFILL, the default padding of spaces is replaced with zeroes.
For example, for a column declared as INT(5) ZEROFILL, a value
of 4 is retrieved as 00004. Note that if you store larger
values than the display width in an integer column, you may experience
problems when MySQL generates temporary tables for some
complicated joins, as in these cases MySQL trusts that the
data did fit into the original column width.
All integral types can have an optional (non-standard) attribute
UNSIGNED. Unsigned values can be used when you want to allow
only positive numbers in a column and you need a little bigger numeric
range for the column.
The FLOAT type is used to represent approximate numeric data
types. The ANSI/ISO SQL92 standard allows an optional specification of
the precision (but not the range of the exponent) in bits following the
keyword FLOAT in parentheses. The MySQL implementation
also supports this optional precision specification. When the keyword
FLOAT is used for a column type without a precision
specification, MySQL uses four bytes to store the values. A
variant syntax is also supported, with two numbers given in parentheses
following the FLOAT keyword. With this option, the first number
continues to represent the storage requirements for the value in bytes,
and the second number specifies the number of digits to be stored and
displayed following the decimal point (as with DECIMAL and
NUMERIC). When MySQL is asked to store a number for
such a column with more decimal digits following the decimal point than
specified for the column, the value is rounded to eliminate the extra
digits when the value is stored.
The REAL and DOUBLE PRECISION types do not accept
precision specifications. As an extension to the ANSI/ISO SQL92
standard, MySQL recognizes DOUBLE as a synonym for the
DOUBLE PRECISION type. In contrast with the standard's
requirement that the precision for REAL be smaller than that used
for DOUBLE PRECISION, MySQL implements both as 8-byte
double-precision floating-point values (when not running in ``ANSI mode'').
For maximum portability, code requiring storage of approximate numeric
data values should use FLOAT or DOUBLE PRECISION with no
specification of precision or number of decimal points.
When asked to store a value in a numeric column that is outside the column type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.
For example, the range of an INT column is -2147483648 to
2147483647. If you try to insert -9999999999 into an
INT column, the value is clipped to the lower endpoint of the range,
and -2147483648 is stored instead. Similarly, if you try to insert
9999999999, 2147483647 is stored instead.
If the INT column is UNSIGNED, the size of the column's
range is the same but its endpoints shift up to 0 and 4294967295.
If you try to store -9999999999 and 9999999999,
the values stored in the column become 0 and 4294967296.
Conversions that occur due to clipping are reported as ``warnings'' for
ALTER TABLE, LOAD DATA INFILE, UPDATE, and
multi-row INSERT statements.
The date and time types are DATETIME, DATE,
TIMESTAMP, TIME, and YEAR. Each of these has a
range of legal values, as well as a ``zero'' value that is used when you
specify a really illegal value. Note that MySQL allows you to store
certain 'not strictly' legal date values, for example 1999-11-31.
The reason for this is that we think it's the responsibility of the
application to handle date checking, not the SQL servers. To make the
date checking 'fast', MySQL only checks that the month is in
the range of 0-12 and the day is in the range of 0-31. The above ranges
are defined this way because MySQL allows you to store, in a
DATE or DATETIME column, dates where the day or month-day
is zero. This is extremely useful for applications that need to store
a birth-date for which you don't know the exact date. In this case you
simply store the date like 1999-00-00 or 1999-01-00. (You
cannot expect to get a correct value from functions like DATE_SUB()
or DATE_ADD for dates like these.)
Here are some general considerations to keep in mind when working with date and time types:
'98-09-04'), rather than
in the month-day-year or day-month-year orders commonly used elsewhere (for
example, '09-04-98', '04-09-98').
TIME values are clipped to
the appropriate endpoint of the TIME range.) The table below
shows the format of the ``zero'' value for each type:
| Column type | ``Zero'' value |
DATETIME | '0000-00-00 00:00:00'
|
DATE | '0000-00-00'
|
TIMESTAMP | 00000000000000 (length depends on display size)
|
TIME | '00:00:00'
|
YEAR | 0000
|
'0' or 0, which are easier to write.
NULL in MyODBC Version 2.50.12 and above,
because ODBC can't handle such values.
MySQL itself is Y2K-safe (see section 1.7 Year 2000 Compliance), but input values presented to MySQL may not be. Any input containing 2-digit year values is ambiguous, because the century is unknown. Such values must be interpreted into 4-digit form because MySQL stores years internally using four digits.
For DATETIME, DATE, TIMESTAMP, and YEAR types,
MySQL interprets dates with ambiguous year values using the
following rules:
00-69 are converted to 2000-2069.
70-99 are converted to 1970-1999.
Remember that these rules provide only reasonable guesses as to what your data mean. If the heuristics used by MySQL don't produce the correct values, you should provide unambiguous input containing 4-digit year values.
ORDER BY will sort 2-digit YEAR/DATE/DATETIME types properly.
Note also that some functions like MIN() and MAX() will convert a
TIMESTAMP/DATE to a number. This means that a timestamp with a
2-digit year will not work properly with these functions. The fix in this
case is to convert the TIMESTAMP/DATE to 4-digit year format or
use something like MIN(DATE_ADD(timestamp,INTERVAL 0 DAYS)).
DATETIME, DATE, and TIMESTAMP Types
The DATETIME, DATE, and TIMESTAMP types are related.
This section describes their characteristics, how they are similar, and how
they differ.
The DATETIME type is used when you need values that contain both date
and time information. MySQL retrieves and displays DATETIME
values in 'YYYY-MM-DD HH:MM:SS' format. The supported range is
'1000-01-01 00:00:00' to '9999-12-31 23:59:59'. (``Supported''
means that although earlier values might work, there is no guarantee that
they will.)
The DATE type is used when you need only a date value, without a time
part. MySQL retrieves and displays DATE values in
'YYYY-MM-DD' format. The supported range is '1000-01-01' to
'9999-12-31'.
The TIMESTAMP column type provides a type that you can use to
automatically mark INSERT or UPDATE operations with the current
date and time. If you have multiple TIMESTAMP columns, only the first
one is updated automatically.
Automatic updating of the first TIMESTAMP column occurs under any of
the following conditions:
INSERT or
LOAD DATA INFILE statement.
UPDATE statement and some
other column changes value. (Note that an UPDATE that sets a column
to the value it already has will not cause the TIMESTAMP column to be
updated, because if you set a column to its current value, MySQL
ignores the update for efficiency.)
TIMESTAMP column to NULL.
TIMESTAMP columns other than the first may also be set to the current
date and time. Just set the column to NULL or to NOW().
You can set any TIMESTAMP column to a value different than the current
date and time by setting it explicitly to the desired value. This is true
even for the first TIMESTAMP column. You can use this property if,
for example, you want a TIMESTAMP to be set to the current date and
time when you create a row, but not to be changed whenever the row is updated
later:
TIMESTAMP column explicitly to its current value.
On the other hand, you may find it just as easy to use a DATETIME
column that you initialize to NOW() when the row is created and
leave alone for subsequent updates.
TIMESTAMP values may range from the beginning of 1970 to sometime in
the year 2037, with a resolution of one second. Values are displayed as
numbers.
The format in which MySQL retrieves and displays TIMESTAMP
values depends on the display size, as illustrated by the table below. The
`full' TIMESTAMP format is 14 digits, but TIMESTAMP columns may
be created with shorter display sizes:
| Column type | Display format |
TIMESTAMP(14) | YYYYMMDDHHMMSS
|
TIMESTAMP(12) | YYMMDDHHMMSS
|
TIMESTAMP(10) | YYMMDDHHMM
|
TIMESTAMP(8) | YYYYMMDD
|
TIMESTAMP(6) | YYMMDD
|
TIMESTAMP(4) | YYMM
|
TIMESTAMP(2) | YY
|
All TIMESTAMP columns have the same storage size, regardless of
display size. The most common display sizes are 6, 8, 12, and 14. You can
specify an arbitrary display size at table creation time, but values of 0 or
greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to
13 are coerced to the next higher even number.
You can specify DATETIME, DATE, and TIMESTAMP values using
any of a common set of formats:
'YYYY-MM-DD HH:MM:SS' or 'YY-MM-DD
HH:MM:SS' format. A ``relaxed'' syntax is allowed--any punctuation
character may be used as the delimiter between date parts or time parts.
For example, '98-12-31 11:30:45', '98.12.31 11+30+45',
'98/12/31 11*30*45', and '98@12@31 11^30^45' are
equivalent.
'YYYY-MM-DD' or 'YY-MM-DD' format.
A ``relaxed'' syntax is allowed here, too. For example, '98-12-31',
'98.12.31', '98/12/31', and '98@12@31' are
equivalent.
'YYYYMMDDHHMMSS' or
'YYMMDDHHMMSS' format, provided that the string makes sense as a
date. For example, '19970523091528' and '970523091528' are
interpreted as '1997-05-23 09:15:28', but '971122129015' is
illegal (it has a nonsensical minute part) and becomes '0000-00-00
00:00:00'.
'YYYYMMDD' or 'YYMMDD'
format, provided that the string makes sense as a date. For example,
'19970523' and '970523' are interpreted as
'1997-05-23', but '971332' is illegal (it has nonsensical month
and day parts) and becomes '0000-00-00'.
YYYYMMDDHHMMSS or YYMMDDHHMMSS
format, provided that the number makes sense as a date. For example,
19830905132800 and 830905132800 are interpreted as
'1983-09-05 13:28:00'.
YYYYMMDD or YYMMDD
format, provided that the number makes sense as a date. For example,
19830905 and 830905 are interpreted as '1983-09-05'.
DATETIME, DATE, or TIMESTAMP context, such as
NOW() or CURRENT_DATE.
Illegal DATETIME, DATE, or TIMESTAMP values are converted
to the ``zero'' value of the appropriate type ('0000-00-00 00:00:00',
'0000-00-00', or 00000000000000).
For values specified as strings that include date part delimiters, it is not
necessary to specify two digits for month or day values that are less than
10. '1979-6-9' is the same as '1979-06-09'. Similarly,
for values specified as strings that include time part delimiters, it is not
necessary to specify two digits for hour, month, or second values that are
less than 10. '1979-10-30 1:2:3' is the same as
'1979-10-30 01:02:03'.
Values specified as numbers should be 6, 8, 12, or 14 digits long. If the
number is 8 or 14 digits long, it is assumed to be in YYYYMMDD or
YYYYMMDDHHMMSS format and that the year is given by the first 4
digits. If the number is 6 or 12 digits long, it is assumed to be in
YYMMDD or YYMMDDHHMMSS format and that the year is given by the
first 2 digits. Numbers that are not one of these lengths are interpreted
as though padded with leading zeros to the closest length.
Values specified as non-delimited strings are interpreted using their length
as given. If the string is 8 or 14 characters long, the year is assumed to
be given by the first 4 characters. Otherwise the year is assumed to be
given by the first 2 characters. The string is interpreted from left to
right to find year, month, day, hour, minute, and second values, for as many
parts as are present in the string. This means you should not use strings
that have fewer than 6 characters. For example, if you specify '9903',
thinking that will represent March, 1999, you will find that MySQL
inserts a ``zero'' date into your table. This is because the year and month
values are 99 and 03, but the day part is missing (zero), so
the value is not a legal date.
TIMESTAMP columns store legal values using the full precision with
which the value was specified, regardless of the display size. This has
several implications:
TIMESTAMP(4) or TIMESTAMP(2). Otherwise, the value will not
be a legal date and 0 will be stored.
ALTER TABLE to widen a narrow TIMESTAMP column,
information will be displayed that previously was ``hidden''.
TIMESTAMP column does not cause information to
be lost, except in the sense that less information is shown when the values
are displayed.
TIMESTAMP values are stored to full precision, the only
function that operates directly on the underlying stored value is
UNIX_TIMESTAMP(). Other functions operate on the formatted retrieved
value. This means you cannot use functions such as HOUR() or
SECOND() unless the relevant part of the TIMESTAMP value is
included in the formatted value. For example, the HH part of a
TIMESTAMP column is not displayed unless the display size is at least
10, so trying to use HOUR() on shorter TIMESTAMP values
produces a meaningless result.
You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information:
DATE value to a DATETIME or TIMESTAMP
object, the time part of the resulting value is set to '00:00:00',
because the DATE value contains no time information.
DATETIME or TIMESTAMP value to a DATE
object, the time part of the resulting value is deleted, because the
DATE type stores no time information.
DATETIME, DATE, and TIMESTAMP
values all can be specified using the same set of formats, the types do not
all have the same range of values. For example, TIMESTAMP values
cannot be earlier than 1970 or later than 2037. This means
that a date such as '1968-01-01', while legal as a DATETIME or
DATE value, is not a valid TIMESTAMP value and will be
converted to 0 if assigned to such an object.
Be aware of certain pitfalls when specifying date values:
'10:11:12' might look like a time value
because of the `:' delimiter, but if used in a date context will be
interpreted as the year '2010-11-12'. The value '10:45:15'
will be converted to '0000-00-00' because '45' is not a legal
month.
00-69 are converted to 2000-2069.
70-99 are converted to 1970-1999.
TIME Type
MySQL retrieves and displays TIME values in 'HH:MM:SS'
format (or 'HHH:MM:SS' format for large hours values). TIME
values may range from '-838:59:59' to '838:59:59'. The reason
the hours part may be so large is that the TIME type may be used not
only to represent a time of day (which must be less than 24 hours), but also
elapsed time or a time interval between two events (which may be much greater
than 24 hours, or even negative).
You can specify TIME values in a variety of formats:
'D HH:MM:SS.fraction' format. (Note that
MySQL doesn't yet store the fraction for the time column). One
can also use one of the following ``relaxed'' syntax:
HH:MM:SS.fraction, HH:MM:SS, HH:MM, D HH:MM:SS,
D HH:MM, D HH or SS. Here D is days between 0-33.
'HHMMSS' format, provided that
it makes sense as a time. For example, '101112' is understood as
'10:11:12', but '109712' is illegal (it has a nonsensical
minute part) and becomes '00:00:00'.
HHMMSS format, provided that it makes sense as a time.
For example, 101112 is understood as '10:11:12'. The following
alternative formats are also understood: SS, MMSS,HHMMSS,
HHMMSS.fraction. Note that MySQL doesn't yet store the
fraction part.
TIME context, such as CURRENT_TIME.
For TIME values specified as strings that include a time part
delimiter, it is not necessary to specify two digits for hours, minutes, or
seconds values that are less than 10. '8:3:2' is the same as
'08:03:02'.
Be careful about assigning ``short'' TIME values to a TIME
column. MySQL interprets values using the assumption that the
rightmost digits represent seconds. (MySQL interprets TIME
values as elapsed time rather than as time of day.) For example, you might
think of '11:12', '1112', and 1112 as meaning
'11:12:00' (12 minutes after 11 o'clock), but MySQL
interprets them as '00:11:12' (11 minutes, 12 seconds). Similarly,
'12' and 12 are interpreted as '00:00:12'.
Values that lie outside the TIME range
but are otherwise legal are clipped to the appropriate
endpoint of the range. For example, '-850:00:00' and
'850:00:00' are converted to '-838:59:59' and
'838:59:59'.
Illegal TIME values are converted to '00:00:00'. Note that
because '00:00:00' is itself a legal TIME value, there is no way
to tell, from a value of '00:00:00' stored in a table, whether the
original value was specified as '00:00:00' or whether it was illegal.
YEAR Type
The YEAR type is a 1-byte type used for representing years.
MySQL retrieves and displays YEAR values in YYYY
format. The range is 1901 to 2155.
You can specify YEAR values in a variety of formats:
'1901' to '2155'.
1901 to 2155.
'00' to '99'. Values in the
ranges '00' to '69' and '70' to '99' are
converted to YEAR values in the ranges 2000 to 2069 and
1970 to 1999.
1 to 99. Values in the
ranges 1 to 69 and 70 to 99 are converted to
YEAR values in the ranges 2001 to 2069 and 1970
to 1999. Note that the range for two-digit numbers is slightly
different than the range for two-digit strings, because you cannot specify zero
directly as a number and have it be interpreted as 2000. You
must specify it as a string '0' or '00' or it will be
interpreted as 0000.
YEAR context, such as NOW().
Illegal YEAR values are converted to 0000.
The string types are CHAR, VARCHAR, BLOB, TEXT,
ENUM, and SET.
CHAR and VARCHAR Types
The CHAR and VARCHAR types are similar, but differ in the
way they are stored and retrieved.
The length of a CHAR column is fixed to the length that you declare
when you create the table. The length can be any value between 1 and 255.
(As of MySQL Version 3.23, the length of CHAR may be 0 to 255.)
When CHAR values are stored, they are right-padded with spaces to the
specified length. When CHAR values are retrieved, trailing spaces are
removed.
Values in VARCHAR columns are variable-length strings. You can
declare a VARCHAR column to be any length between 1 and 255, just as
for CHAR columns. However, in contrast to CHAR, VARCHAR
values are stored using only as many characters as are needed, plus one byte
to record the length. Values are not padded; instead, trailing spaces are
removed when values are stored. (This space removal differs from the ANSI
SQL specification.)
If you assign a value to a CHAR or VARCHAR column that
exceeds the column's maximum length, the value is truncated to fit.
The table below illustrates the differences between the two types of columns
by showing the result of storing various string values into CHAR(4)
and VARCHAR(4) columns:
| Value | CHAR(4) | Storage required | VARCHAR(4) | Storage required |
'' | ' ' | 4 bytes | '' | 1 byte |
'ab' | 'ab ' | 4 bytes | 'ab' | 3 bytes |
'abcd' | 'abcd' | 4 bytes | 'abcd' | 5 bytes |
'abcdefgh' | 'abcd' | 4 bytes | 'abcd' | 5 bytes |
The values retrieved from the CHAR(4) and VARCHAR(4) columns
will be the same in each case, because trailing spaces are removed from
CHAR columns upon retrieval.
Values in CHAR and VARCHAR columns are sorted and compared
in case-insensitive fashion, unless the BINARY attribute was
specified when the table was created. The BINARY attribute means
that column values are sorted and compared in case-sensitive fashion
according to the ASCII order of the machine where the MySQL
server is running. BINARY doesn't affect how the column is stored
or retrieved.
The BINARY attribute is sticky. This means that if a column marked
BINARY is used in an expression, the whole expression is compared as a
BINARY value.
MySQL may silently change the type of a CHAR or VARCHAR
column at table creation time.
See section 7.7.1 Silent Column Specification Changes.
BLOB and TEXT Types
A BLOB is a binary large object that can hold a variable amount of
data. The four BLOB types TINYBLOB, BLOB,
MEDIUMBLOB, and LONGBLOB differ only in the maximum length of
the values they can hold.
See section 7.3.1 Column Type Storage Requirements.
The four TEXT types TINYTEXT, TEXT, MEDIUMTEXT,
and LONGTEXT correspond to the four BLOB types and have the
same maximum lengths and storage requirements. The only difference between
BLOB and TEXT types is that sorting and comparison is performed
in case-sensitive fashion for BLOB values and case-insensitive fashion
for TEXT values. In other words, a TEXT is a case-insensitive
BLOB.
If you assign a value to a BLOB or TEXT column that exceeds
the column type's maximum length, the value is truncated to fit.
In most respects, you can regard a TEXT column as a VARCHAR
column that can be as big as you like. Similarly, you can regard a
BLOB column as a VARCHAR BINARY column. The differences are:
BLOB and TEXT columns with
MySQL Version 3.23.2 and newer. Older versions of
MySQL did not support this.
BLOB and TEXT columns
when values are stored, as there is for VARCHAR columns.
BLOB and TEXT columns cannot have DEFAULT values.
MyODBC defines BLOB values as LONGVARBINARY and
TEXT values as LONGVARCHAR.
Because BLOB and TEXT values may be extremely long, you
may run up against some constraints when using them:
GROUP BY or ORDER BY on a BLOB or
TEXT column, you must convert the column value into a fixed-length
object. The standard way to do this is with the SUBSTRING
function. For example:
mysql> select comment from tbl_name,substring(comment,20) as substr
ORDER BY substr;
If you don't do this, only the first max_sort_length bytes of the
column are used when sorting. The default value of max_sort_length is
1024; this value can be changed using the -O option when starting the
mysqld server. You can group on an expression involving BLOB or
TEXT values by specifying the column position or by using an alias:
mysql> select id,substring(blob_col,1,100) from tbl_name
GROUP BY 2;
mysql> select id,substring(blob_col,1,100) as b from tbl_name
GROUP BY b;
BLOB or TEXT object is determined by its
type, but the largest value you can actually transmit between the client and
server is determined by the amount of available memory and the size of the
communications buffers. You can change the message buffer size, but you must
do so on both the server and client ends. See section 12.2.3 Tuning Server Parameters.
Note that each BLOB or TEXT value is represented
internally by a separately allocated object. This is in contrast to all
other column types, for which storage is allocated once per column when
the table is opened.
ENUM Type
An ENUM is a string object whose value normally is chosen from a list
of allowed values that are enumerated explicitly in the column specification
at table creation time.
The value may also be the empty string ("") or NULL under
certain circumstances:
ENUM (that is, a string not
present in the list of allowed values), the empty string is inserted
instead as a special error value.
ENUM is declared NULL, NULL is also a legal value
for the column, and the default value is NULL. If an ENUM is
declared NOT NULL, the default value is the first element of the
list of allowed values.
Each enumeration value has an index:
SELECT statement to find rows into which invalid
ENUM values were assigned:
mysql> SELECT * FROM tbl_name WHERE enum_col=0;
NULL value is NULL.
For example, a column specified as ENUM("one", "two", "three") can
have any of the values shown below. The index of each value is also shown:
| Value | Index |
NULL | NULL
|
"" | 0 |
"one" | 1 |
"two" | 2 |
"three" | 3 |
An enumeration can have a maximum of 65535 elements.
Lettercase is irrelevant when you assign values to an ENUM column.
However, values retrieved from the column later have lettercase matching the
values that were used to specify the allowable values at table creation time.
If you retrieve an ENUM in a numeric context, the column value's
index is returned. For example, you can retrieve numeric values from
an ENUM column like this:
mysql> SELECT enum_col+0 FROM tbl_name;
If you store a number into an ENUM, the number is treated as an
index, and the value stored is the enumeration member with that index.
(However, this will not work with LOAD DATA, which treats all
input as strings.)
ENUM values are sorted according to the order in which the enumeration
members were listed in the column specification. (In other words,
ENUM values are sorted according to their index numbers.) For
example, "a" sorts before "b" for ENUM("a", "b"), but
"b" sorts before "a" for ENUM("b", "a"). The empty
string sorts before non-empty strings, and NULL values sort before
all other enumeration values.
If you want to get all possible values for an ENUM column, you should
use: SHOW COLUMNS FROM table_name LIKE enum_column_name and parse
the ENUM definition in the second column.
SET Type
A SET is a string object that can have zero or more values, each of
which must be chosen from a list of allowed values specified when the table
is created. SET column values that consist of multiple set members
are specified with members separated by commas (`,'). A consequence of
this is that SET member values cannot themselves contain commas.
For example, a column specified as SET("one", "two") NOT NULL can have
any of these values:
"" "one" "two" "one,two"
A SET can have a maximum of 64 different members.
MySQL stores SET values numerically, with the low-order bit
of the stored value corresponding to the first set member. If you retrieve a
SET value in a numeric context, the value retrieved has bits set
corresponding to the set members that make up the column value. For example,
you can retrieve numeric values from a SET column like this:
mysql> SELECT set_col+0 FROM tbl_name;
If a number is stored into a SET column, the bits that
are set in the binary representation of the number determine the
set members in the column value. Suppose a column is specified as
SET("a","b","c","d"). Then the members have the following bit
values:
SET member | Decimal value | Binary value |
a | 1 | 0001
|
b | 2 | 0010
|
c | 4 | 0100
|
d | 8 | 1000
|
If you assign a value of 9 to this column, that is 1001 in
binary, so the first and fourth SET value members "a" and
"d" are selected and the resulting value is "a,d".
For a value containing more than one SET element, it does not matter
what order the elements are listed in when you insert the value. It also
does not matter how many times a given element is listed in the value.
When the value is retrieved later, each element in the value will appear
once, with elements listed according to the order in which they were
specified at table creation time. For example, if a column is specified as
SET("a","b","c","d"), then "a,d", "d,a", and
"d,a,a,d,d" will all appear as "a,d" when retrieved.
SET values are sorted numerically. NULL values sort before
non-NULL SET values.
Normally, you perform a SELECT on a SET column using
the LIKE operator or the FIND_IN_SET() function:
mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%';
mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0;
But the following will also work:
mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; mysql> SELECT * FROM tbl_name WHERE set_col & 1;
The first of these statements looks for an exact match. The second looks for values containing the first set member.
If you want to get all possible values for a SET column, you should
use: SHOW COLUMNS FROM table_name LIKE set_column_name and parse
the SET definition in the second column.
For the most efficient use of storage, try to use the most precise type in
all cases. For example, if an integer column will be used for values in the
range between 1 and 99999, MEDIUMINT UNSIGNED is the
best type.
Accurate representation of monetary values is a common problem. In
MySQL, you should use the DECIMAL type. This is stored as
a string, so no loss of accuracy should occur. If accuracy is not
too important, the DOUBLE type may also be good enough.
For high precision, you can always convert to a fixed-point type stored
in a BIGINT. This allows you to do all calculations with integers
and convert results back to floating-point values only when necessary.
All MySQL column types can be indexed. Use of indexes on the
relevant columns is the best way to improve the performance of SELECT
operations.
A table may have up to 16 indexes. The maximum index length is 256 bytes, although this may be changed when compiling MySQL.
For CHAR and VARCHAR columns, you can index a prefix of a
column. This is much faster and requires less disk space than indexing the
whole column. The syntax to use in the CREATE TABLE statement to
index a column prefix looks like this:
KEY index_name (col_name(length))
The example below creates an index for the first 10 characters of the
name column:
mysql> CREATE TABLE test (
name CHAR(200) NOT NULL,
KEY index_name (name(10)));
For BLOB and TEXT columns, you must index a prefix of the
column. You cannot index the entire column.
In MySQL Version 3.23.23 or later, you can also create special
FULLTEXT indexes. They are used for full-text search. Only the
MyISAM table type supports FULLTEXT indexes. They can be
created only from VARCHAR and TEXT columns.
Indexing always happens over the entire column and partial indexing is not
supported. See section 24.2 MySQL Full-text Search for details.
MySQL can create indexes on multiple columns. An index may
consist of up to 15 columns. (On CHAR and VARCHAR columns you
can also use a prefix of the column as a part of an index).
A multiple-column index can be considered a sorted array containing values that are created by concatenating the values of the indexed columns.
MySQL uses multiple-column indexes in such a way that queries are
fast when you specify a known quantity for the first column of the index in a
WHERE clause, even if you don't specify values for the other columns.
Suppose a table is created using the following specification:
mysql> CREATE TABLE test (
id INT NOT NULL,
last_name CHAR(30) NOT NULL,
first_name CHAR(30) NOT NULL,
PRIMARY KEY (id),
INDEX name (last_name,first_name));
Then the index name is an index over last_name and
first_name. The index will be used for queries that specify
values in a known range for last_name, or for both last_name
and first_name.
Therefore, the name index will be used in the following queries:
mysql> SELECT * FROM test WHERE last_name="Widenius";
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND first_name="Michael";
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND (first_name="Michael" OR first_name="Monty");
mysql> SELECT * FROM test WHERE last_name="Widenius"
AND first_name >="M" AND first_name < "N";
However, the name index will NOT be used in the following queries:
mysql> SELECT * FROM test WHERE first_name="Michael";
mysql> SELECT * FROM test WHERE last_name="Widenius"
OR first_name="Michael";
For more information on the manner in which MySQL uses indexes to improve query performance, see section 12.4 How MySQL Uses Indexes.
To make it easier to use code written for SQL implementations from other vendors, MySQL maps column types as shown in the table below. These mappings make it easier to move table definitions from other database engines to MySQL:
| Other vendor type | MySQL type |
BINARY(NUM) | CHAR(NUM) BINARY
|
CHAR VARYING(NUM) | VARCHAR(NUM)
|
FLOAT4 | FLOAT
|
FLOAT8 | DOUBLE
|
INT1 | TINYINT
|
INT2 | SMALLINT
|
INT3 | MEDIUMINT
|
INT4 | INT
|
INT8 | BIGINT
|
LONG VARBINARY | MEDIUMBLOB
|
LONG VARCHAR | MEDIUMTEXT
|
MIDDLEINT | MEDIUMINT
|
VARBINARY(NUM) | VARCHAR(NUM) BINARY
|
Column type mapping occurs at table creation time. If you create a table
with types used by other vendors and then issue a DESCRIBE tbl_name
statement, MySQL reports the table structure using the equivalent
MySQL types.
SELECT and WHERE Clauses
A select_expression or where_definition in a SQL statement
can consist of any expression using the functions described below.
An expression that contains NULL always produces a NULL value
unless otherwise indicated in the documentation for the operators and
functions involved in the expression.
NOTE: There must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around arguments are permitted, though.
You can force MySQL to accept spaces after the function name by
starting mysqld with --ansi or using the
CLIENT_IGNORE_SPACE to mysql_connect(), but in this case all
function names will become reserved words. See section 5.2 Running MySQL in ANSI Mode.
For the sake of brevity, examples display the output from the mysql
program in abbreviated form. So this:
mysql> select MOD(29,9); 1 rows in set (0.00 sec) +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+
is displayed like this:
mysql> select MOD(29,9);
-> 2
( ... )
mysql> select 1+2*3;
-> 7
mysql> select (1+2)*3;
-> 9
The usual arithmetic operators are available. Note that in the case of
`-', `+', and `*', the result is calculated with
BIGINT (64-bit) precision if both arguments are integers!
+
mysql> select 3+5;
-> 8
-
mysql> select 3-5;
-> -2
*
mysql> select 3*5;
-> 15
mysql> select 18014398509481984*18014398509481984.0;
-> 324518553658426726783156020576256.0
mysql> select 18014398509481984*18014398509481984;
-> 0
The result of the last expression is incorrect because the result of the integer
multiplication exceeds the 64-bit range of BIGINT calculations.
/
mysql> select 3/5;
-> 0.60
Division by zero produces a NULL result:
mysql> select 102/(1-1);
-> NULL
A division will be calculated with BIGINT arithmetic only if performed
in a context where its result is converted to an integer!
MySQL uses BIGINT (64-bit) arithmetic for bit operations, so
these operators have a maximum range of 64 bits.
|
mysql> select 29 | 15;
-> 31
&
mysql> select 29 & 15;
-> 13
<<
BIGINT) number to the left:
mysql> select 1 << 2
-> 4
>>
BIGINT) number to the right:
mysql> select 4 >> 2
-> 1
~
mysql> select 5 & ~1
-> 4
BIT_COUNT(N)
N:
mysql> select BIT_COUNT(29);
-> 4
All logical functions return 1 (TRUE) or 0 (FALSE):
NOT
!
1 if the argument is 0, otherwise returns
0.
Exception: NOT NULL returns NULL:
mysql> select NOT 1;
-> 0
mysql> select NOT NULL;
-> NULL
mysql> select ! (1+1);
-> 0
mysql> select ! 1+1;
-> 1
The last example returns 1 because the expression evaluates
the same way as (!1)+1.
OR
||
1 if either argument is not 0 and not
NULL:
mysql> select 1 || 0;
-> 1
mysql> select 0 || 0;
-> 0
mysql> select 1 || NULL;
-> 1
AND
&&
0 if either argument is 0 or NULL,
otherwise returns 1:
mysql> select 1 && NULL;
-> 0
mysql> select 1 && 0;
-> 0
Comparison operations result in a value of 1 (TRUE), 0 (FALSE),
or NULL. These functions work for both numbers and strings. Strings
are automatically converted to numbers and numbers to strings as needed (as
in Perl).
MySQL performs comparisons using the following rules:
NULL, the result of the comparison
is NULL, except for the <=> operator.
TIMESTAMP or DATETIME column and
the other argument is a constant, the constant is converted
to a timestamp before the comparison is performed. This is done to be more
ODBC-friendly.
By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English).
The examples below illustrate conversion of strings to numbers for comparison operations:
mysql> SELECT 1 > '6x';
-> 0
mysql> SELECT 7 > '6x';
-> 1
mysql> SELECT 0 > 'x6';
-> 0
mysql> SELECT 0 = 'x6';
-> 1
=
mysql> select 1 = 0;
-> 0
mysql> select '0' = 0;
-> 1
mysql> select '0.0' = 0;
-> 1
mysql> select '0.01' = 0;
-> 0
mysql> select '.01' = 0.01;
-> 1
<>
!=
mysql> select '.01' <> '0.01';
-> 1
mysql> select .01 <> '0.01';
-> 0
mysql> select 'zapp' <> 'zappp';
-> 1
<=
mysql> select 0.1 <= 2;
-> 1
<
mysql> select 2 <= 2;
-> 1
>=
mysql> select 2 >= 2;
-> 1
>
mysql> select 2 > 2;
-> 0
<=>
mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1 1 0
IS NULL
IS NOT NULL
NULL:
mysql> select 1 IS NULL, 0 IS NULL, NULL IS NULL:
-> 0 0 1
mysql> select 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
-> 1 1 0
expr BETWEEN min AND max
expr is greater than or equal to min and expr is
less than or equal to max, BETWEEN returns 1,
otherwise it returns 0. This is equivalent to the expression
(min <= expr AND expr <= max) if all the arguments are of the
same type. The first argument (expr) determines how the
comparison is performed as follows:
expr is a TIMESTAMP, DATE, or DATETIME
column, MIN() and MAX() are formatted to the same format if
they are constants.
expr is a case-insensitive string expression, a case-insensitive
string comparison is done.
expr is a case-sensitive string expression, a case-sensitive
string comparison is done.
expr is an integer expression, an integer comparison is done.
mysql> select 1 BETWEEN 2 AND 3;
-> 0
mysql> select 'b' BETWEEN 'a' AND 'c';
-> 1
mysql> select 2 BETWEEN 2 AND '3';
-> 1
mysql> select 2 BETWEEN 2 AND 'x-3';
-> 0
expr IN (value,...)
1 if expr is any of the values in the IN list,
else returns 0. If all values are constants, then all values are
evaluated according to the type of expr and sorted. The search for the
item is then done using a binary search. This means IN is very quick
if the IN value list consists entirely of constants. If expr
is a case-sensitive string expression, the string comparison is performed in
case-sensitive fashion:
mysql> select 2 IN (0,3,5,'wefwf');
-> 0
mysql> select 'wefwf' IN (0,3,5,'wefwf');
-> 1
expr NOT IN (value,...)
NOT (expr IN (value,...)).
ISNULL(expr)
expr is NULL, ISNULL() returns 1, otherwise
it returns 0:
mysql> select ISNULL(1+1);
-> 0
mysql> select ISNULL(1/0);
-> 1
Note that a comparison of NULL values using = will always be
false!
COALESCE(list)
NULL element in list:
mysql> select COALESCE(NULL,1);
-> 1
mysql> select COALESCE(NULL,NULL,NULL);
-> NULL
INTERVAL(N,N1,N2,N3,...)
0 if N < N1, 1 if N < N2
and so on. All arguments are treated as integers. It is required that
N1 < N2 < N3 < ... < Nn for this function
to work correctly. This is because a binary search is used (very fast):
mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200);
-> 3
mysql> select INTERVAL(10, 1, 10, 100, 1000);
-> 2
mysql> select INTERVAL(22, 23, 30, 44, 200);
-> 0
Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.
expr LIKE pat [ESCAPE 'escape-char']
1 (TRUE) or 0
(FALSE). With LIKE you can use the following two wild-card characters
in the pattern:
% | Matches any number of characters, even zero characters |
_ | Matches exactly one character |
mysql> select 'David!' LIKE 'David_';
-> 1
mysql> select 'David!' LIKE '%D%v%';
-> 1
To test for literal instances of a wild-card character, precede the character
with the escape character. If you don't specify the ESCAPE character,
`\' is assumed:
\% | Matches one % character
|
\_ | Matches one _ character
|
mysql> select 'David!' LIKE 'David\_';
-> 0
mysql> select 'David_' LIKE 'David\_';
-> 1
To specify a different escape character, use the ESCAPE clause:
mysql> select 'David_' LIKE 'David|_' ESCAPE '|';
-> 1
LIKE is allowed on numeric expressions! (This is a MySQL
extension to the ANSI SQL LIKE.)
mysql> select 10 LIKE '1%';
-> 1
Note: Because MySQL uses the C escape syntax in strings (for example,
`\n'), you must double any `\' that you use in your LIKE
strings. For example, to search for `\n', specify it as `\\n'. To
search for `\', specify it as `\\\\' (the backslashes are stripped
once by the parser and another time when the pattern match is done, leaving
a single backslash to be matched).
expr NOT LIKE pat [ESCAPE 'escape-char']
NOT (expr LIKE pat [ESCAPE 'escape-char']).
expr REGEXP pat
expr RLIKE pat
expr against a pattern
pat. The pattern can be an extended regular expression.
See section I Description of MySQL regular expression syntax. Returns 1 if expr matches pat, otherwise
returns 0. RLIKE is a synonym for REGEXP, provided for
mSQL compatibility. Note: Because MySQL uses the C escape
syntax in strings (for example, `\n'), you must double any `\' that
you use in your REGEXP strings. As of MySQL Version 3.23.4,
REGEXP is case insensitive for normal (not binary) strings:
mysql> select 'Monty!' REGEXP 'm%y%%';
-> 0
mysql> select 'Monty!' REGEXP '.*';
-> 1
mysql> select 'new*\n*line' REGEXP 'new\\*.\\*line';
-> 1
mysql> select "a" REGEXP "A", "a" REGEXP BINARY "A";
-> 1 0
REGEXP and RLIKE use the current character set (ISO-8859-1
Latin1 by default) when deciding the type of a character.
expr NOT REGEXP pat
expr NOT RLIKE pat
NOT (expr REGEXP pat).
STRCMP(expr1,expr2)
STRCMP()
returns 0 if the strings are the same, -1 if the first
argument is smaller than the second according to the current sort order,
and 1 otherwise:
mysql> select STRCMP('text', 'text2');
-> -1
mysql> select STRCMP('text2', 'text');
-> 1
mysql> select STRCMP('text', 'text');
-> 0
MATCH (col1,col2,...) AGAINST (expr)
MATCH ... AGAINST() is used for full-text search and returns
relevance - similarity measure between the text in columns
(col1,col2,...) and the query expr. Relevance is a
positive floating-point number. Zero relevance means no similarity.
For MATCH ... AGAINST() to work, a FULLTEXT index
must be created first. See section 7.7 CREATE TABLE Syntax.
MATCH ... AGAINST() is available in MySQL Version
3.23.23 or later. For details and usage examples
see section 24.2 MySQL Full-text Search.
BINARYBINARY operator casts the string following it to a binary string.
This is an easy way to force a column comparison to be case sensitive even
if the column isn't defined as BINARY or BLOB:
mysql> select "a" = "A";
-> 1
mysql> select BINARY "a" = "A";
-> 0
BINARY was introduced in MySQL Version 3.23.0.
Note that in some context MySQL will not be able to use the
index efficiently when you cast an indexed column to BINARY.
IFNULL(expr1,expr2)
expr1 is not NULL, IFNULL() returns expr1,
else it returns expr2. IFNULL() returns a numeric or string
value, depending on the context in which it is used:
mysql> select IFNULL(1,0);
-> 1
mysql> select IFNULL(NULL,10);
-> 10
mysql> select IFNULL(1/0,10);
-> 10
mysql> select IFNULL(1/0,'yes');
-> 'yes'
NULLIF(expr1,expr2)
expr1 = expr2 is true, return NULL else return expr1.
This is the same as CASE WHEN x = y THEN NULL ELSE x END:
mysql> select NULLIF(1,1);
-> NULL
mysql> select NULLIF(1,2);
-> 1
Note that expr1 is evaluated twice in MySQL if the arguments
are equal.
IF(expr1,expr2,expr3)
expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then
IF() returns expr2, else it returns expr3.
IF() returns a numeric or string value, depending on the context
in which it is used:
mysql> select IF(1>2,2,3);
-> 3
mysql> select IF(1<2,'yes','no');
-> 'yes'
mysql> select IF(strcmp('test','test1'),'no','yes');
-> 'no'
expr1 is evaluated as an integer value, which means that if you are
testing floating-point or string values, you should do so using a comparison
operation:
mysql> select IF(0.1,1,0);
-> 0
mysql> select IF(0.1<>0,1,0);
-> 1
In the first case above, IF(0.1) returns 0 because 0.1
is converted to an integer value, resulting in a test of IF(0). This
may not be what you expect. In the second case, the comparison tests the
original floating-point value to see whether it is non-zero. The result
of the comparison is used as an integer.
The default return type of IF() (which may matter when it is
stored into a temporary table) is calculated in MySQL Version
3.23 as follows:
| Expression | Return value |
| expr2 or expr3 returns string | string |
| expr2 or expr3 returns a floating-point value | floating-point |
| expr2 or expr3 returns an integer | integer |
CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END
CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END
result where
value=compare-value. The second version returns the result for
the first condition, which is true. If there was no matching result
value, then the result after ELSE is returned. If there is no
ELSE part then NULL is returned:
mysql> SELECT CASE 1 WHEN 1 THEN "one" WHEN 2 THEN "two" ELSE "more" END;
-> "one"
mysql> SELECT CASE WHEN 1>0 THEN "true" ELSE "false" END;
-> "true"
mysql> SELECT CASE BINARY "B" when "a" then 1 when "b" then 2 END;
-> NULL
All mathematical functions return NULL in case of an error.
-
mysql> select - 2;
-> -2
Note that if this operator is used with a BIGINT, the return value is a
BIGINT! This means that you should avoid using - on integers that
may have the value of -2^63!
ABS(X)
X:
mysql> select ABS(2);
-> 2
mysql> select ABS(-32);
-> 32
This function is safe to use with BIGINT values.
SIGN(X)
-1, 0, or 1, depending
on whether X is negative, zero, or positive:
mysql> select SIGN(-32);
-> -1
mysql> select SIGN(0);
-> 0
mysql> select SIGN(234);
-> 1
MOD(N,M)
%
% operator in C).
Returns the remainder of N divided by M:
mysql> select MOD(234, 10);
-> 4
mysql> select 253 % 7;
-> 1
mysql> select MOD(29,9);
-> 2
This function is safe to use with BIGINT values.
FLOOR(X)
X:
mysql> select FLOOR(1.23);
-> 1
mysql> select FLOOR(-1.23);
-> -2
Note that the return value is converted to a BIGINT!
CEILING(X)
X:
mysql> select CEILING(1.23);
-> 2
mysql> select CEILING(-1.23);
-> -1
Note that the return value is converted to a BIGINT!
ROUND(X)
X, rounded to the nearest integer:
mysql> select ROUND(-1.23);
-> -1
mysql> select ROUND(-1.58);
-> -2
mysql> select ROUND(1.58);
-> 2
ROUND(X,D)
X, rounded to a number with D decimals.
If D is 0, the result will have no decimal point or fractional
part:
mysql> select ROUND(1.298, 1);
-> 1.3
mysql> select ROUND(1.298, 0);
-> 1
EXP(X)
e (the base of natural logarithms) raised to
the power of X:
mysql> select EXP(2);
-> 7.389056
mysql> select EXP(-2);
-> 0.135335
LOG(X)
X:
mysql> select LOG(2);
-> 0.693147
mysql> select LOG(-2);
-> NULL
If you want the log of a number X to some arbitary base B, use
the formula LOG(X)/LOG(B).
LOG10(X)
X:
mysql> select LOG10(2);
-> 0.301030
mysql> select LOG10(100);
-> 2.000000
mysql> select LOG10(-100);
-> NULL
POW(X,Y)
POWER(X,Y)
X raised to the power of Y:
mysql> select POW(2,2);
-> 4.000000
mysql> select POW(2,-2);
-> 0.250000
SQRT(X)
X:
mysql> select SQRT(4);
-> 2.000000
mysql> select SQRT(20);
-> 4.472136
PI()
mysql> select PI();
-> 3.141593
COS(X)
X, where X is given in radians:
mysql> select COS(PI());
-> -1.000000
SIN(X)
X, where X is given in radians:
mysql> select SIN(PI());
-> 0.000000
TAN(X)
X, where X is given in radians:
mysql> select TAN(PI()+1);
-> 1.557408
ACOS(X)
X, that is, the value whose cosine is
X. Returns NULL if X is not in the range -1 to
1:
mysql> select ACOS(1);
-> 0.000000
mysql> select ACOS(1.0001);
-> NULL
mysql> select ACOS(0);
-> 1.570796
ASIN(X)
X, that is, the value whose sine is
X. Returns NULL if X is not in the range -1 to
1:
mysql> select ASIN(0.2);
-> 0.201358
mysql> select ASIN('foo');
-> 0.000000
ATAN(X)
X, that is, the value whose tangent is
X:
mysql> select ATAN(2);
-> 1.107149
mysql> select ATAN(-2);
-> -1.107149
ATAN2(Y,X)
X and Y. It is
similar to calculating the arc tangent of Y / X, except that the
signs of both arguments are used to determine the quadrant of the
result:
mysql> select ATAN(-2,2);
-> -0.785398
mysql> select ATAN(PI(),0);
-> 1.570796
COT(X)
X:
mysql> select COT(12);
-> -1.57267341
mysql> select COT(0);
-> NULL
RAND()
RAND(N)
0 to 1.0.
If an integer argument N is specified, it is used as the seed value:
mysql> select RAND();
-> 0.5925
mysql> select RAND(20);
-> 0.1811
mysql> select RAND(20);
-> 0.1811
mysql> select RAND();
-> 0.2079
mysql> select RAND();
-> 0.7888
You can't use a column with RAND() values in an ORDER BY
clause, because ORDER BY would evaluate the column multiple times.
In MySQL Version 3.23, you can, however, do:
SELECT * FROM table_name ORDER BY RAND()
This is useful to get a random sample of a set SELECT * FROM
table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000.
Note that a RAND() in a WHERE clause will be re-evaluated
every time the WHERE is executed.
LEAST(X,Y,...)
INTEGER context, or all arguments
are integer-valued, they are compared as integers.
REAL context, or all arguments are
real-valued, they are compared as reals.
mysql> select LEAST(2,0);
-> 0
mysql> select LEAST(34.0,3.0,5.0,767.0);
-> 3.0
mysql> select LEAST("B","A","C");
-> "A"
In MySQL versions prior to Version 3.22.5, you can use MIN()
instead of LEAST.
GREATEST(X,Y,...)
LEAST:
mysql> select GREATEST(2,0);
-> 2
mysql> select GREATEST(34.0,3.0,5.0,767.0);
-> 767.0
mysql> select GREATEST("B","A","C");
-> "C"
In MySQL versions prior to Version 3.22.5, you can use MAX()
instead of GREATEST.
DEGREES(X)
X, converted from radians to degrees:
mysql> select DEGREES(PI());
-> 180.000000
RADIANS(X)
X, converted from degrees to radians:
mysql> select RADIANS(90);
-> 1.570796
TRUNCATE(X,D)
X, truncated to D decimals. If D
is 0, the result will have no decimal point or fractional part:
mysql> select TRUNCATE(1.223,1);
-> 1.2
mysql> select TRUNCATE(1.999,1);
-> 1.9
mysql> select TRUNCATE(1.999,0);
-> 1
String-valued functions return NULL if the length of the result would
be greater than the max_allowed_packet server parameter. See section 12.2.3 Tuning Server Parameters.
For functions that operate on string positions, the first position is numbered 1.
ASCII(str)
str. Returns 0 if str is the empty string. Returns
NULL if str is NULL:
mysql> select ASCII('2');
-> 50
mysql> select ASCII(2);
-> 50
mysql> select ASCII('dx');
-> 100
See also the ORD() function.
ORD(str)
((first byte ASCII code)*256+(second byte ASCII code))[*256+third byte ASCII code...].
If the leftmost character is not a multi-byte character, returns the same
value as the like ASCII() function does:
mysql> select ORD('2');
-> 50
CONV(N,from_base,to_base)
N, converted from base from_base
to base to_base. Returns NULL if any argument is NULL.
The argument N is interpreted as an integer, but may be specified as
an integer or a string. The minimum base is 2 and the maximum base is
36. If to_base is a negative number, N is regarded as a
signed number. Otherwise, N is treated as unsigned. CONV works
with 64-bit precision:
mysql> select CONV("a",16,2);
-> '1010'
mysql> select CONV("6E",18,8);
-> '172'
mysql> select CONV(-17,10,-18);
-> '-H'
mysql> select CONV(10+"10"+'10'+0xa,10,10);
-> '40'
BIN(N)
N, where
N is a longlong (BIGINT) number. This is equivalent to
CONV(N,10,2). Returns NULL if N is NULL:
mysql> select BIN(12);
-> '1100'
OCT(N)
N, where
N is a longlong number. This is equivalent to CONV(N,10,8).
Returns NULL if N is NULL:
mysql> select OCT(12);
-> '14'
HEX(N)
N, where
N is a longlong (BIGINT) number. This is equivalent to
CONV(N,10,16). Returns NULL if N is NULL:
mysql> select HEX(255);
-> 'FF'
CHAR(N,...)
CHAR() interprets the arguments as integers and returns a string
consisting of the characters given by the ASCII code values of those
integers. NULL values are skipped:
mysql> select CHAR(77,121,83,81,'76');
-> 'MySQL'
mysql> select CHAR(77,77.3,'77.3');
-> 'MMM'
CONCAT(str1,str2,...)
NULL if any argument is NULL. May have more than 2 arguments.
A numeric argument is converted to the equivalent string form:
mysql> select CONCAT('My', 'S', 'QL');
-> 'MySQL'
mysql> select CONCAT('My', NULL, 'QL');
-> NULL
mysql> select CONCAT(14.3);
-> '14.3'
CONCAT_WS(separator, str1, str2,...)
CONCAT_WS() stands for CONCAT With Separator and is a special form of
CONCAT(). The first argument is the separator for the rest of the
arguments. The separator can be a string as well as the rest of the
arguments. If the separator is NULL, the result will be NULL.
The function will skip any NULLs and empty strings, after the
separator argument. The separator will be added between the strings to be
concatenated:
mysql> select CONCAT_WS(",","First name","Second name","Last Name");
-> 'First name,Second name,Last Name'
mysql> select CONCAT_WS(",","First name",NULL,"Last Name");
-> 'First name,Last Name'
LENGTH(str)
OCTET_LENGTH(str)
CHAR_LENGTH(str)
CHARACTER_LENGTH(str)
str:
mysql> select LENGTH('text');
-> 4
mysql> select OCTET_LENGTH('text');
-> 4
Note that for CHAR_LENGTH(), multi-byte characters are only counted
once.
LOCATE(substr,str)
POSITION(substr IN str)
substr
in string str. Returns 0 if substr is not in str:
mysql> select LOCATE('bar', 'foobarbar');
-> 4
mysql> select LOCATE('xbar', 'foobar');
-> 0
This function is multi-byte safe.
LOCATE(substr,str,pos)
substr in
string str, starting at position pos.
Returns 0 if substr is not in str:
mysql> select LOCATE('bar', 'foobarbar',5);
-> 7
This function is multi-byte safe.
INSTR(str,substr)
substr in
string str. This is the same as the two-argument form of
LOCATE(), except that the arguments are swapped:
mysql> select INSTR('foobarbar', 'bar');
-> 4
mysql> select INSTR('xbar', 'foobar');
-> 0
This function is multi-byte safe.
LPAD(str,len,padstr)
str, left-padded with the string padstr
until str is len characters long. If str is longer
than len' then it will be shortened to len characters.
mysql> select LPAD('hi',4,'??');
-> '??hi'
RPAD(str,len,padstr)
str, right-padded with the string
padstr until str is len characters long. If
str is longer than len' then it will be shortened to
len characters.
mysql> select RPAD('hi',5,'?');
-> 'hi???'
LEFT(str,len)
len characters from the string str:
mysql> select LEFT('foobarbar', 5);
-> 'fooba'
This function is multi-byte safe.
RIGHT(str,len)
len characters from the string str:
mysql> select RIGHT('foobarbar', 4);
-> 'rbar'
This function is multi-byte safe.
SUBSTRING(str,pos,len)
SUBSTRING(str FROM pos FOR len)
MID(str,pos,len)
len characters long from string str,
starting at position pos.
The variant form that uses FROM is ANSI SQL92 syntax:
mysql> select SUBSTRING('Quadratically',5,6);
-> 'ratica'
This function is multi-byte safe.
SUBSTRING(str,pos)
SUBSTRING(str FROM pos)
str starting at position pos:
mysql> select SUBSTRING('Quadratically',5);
-> 'ratically'
mysql> select SUBSTRING('foobarbar' FROM 4);
-> 'barbar'
This function is multi-byte safe.
SUBSTRING_INDEX(str,delim,count)
str before count
occurrences of the delimiter delim.
If count is positive, everything to the left of the final delimiter
(counting from the left) is returned.
If count is negative, everything to the right of the final delimiter
(counting from the right) is returned:
mysql> select SUBSTRING_INDEX('www.mysql.com', '.', 2);
-> 'www.mysql'
mysql> select SUBSTRING_INDEX('www.mysql.com', '.', -2);
-> 'mysql.com'
This function is multi-byte safe.
LTRIM(str)
str with leading space characters removed:
mysql> select LTRIM(' barbar');
-> 'barbar'
RTRIM(str)
str with trailing space characters removed:
mysql> select RTRIM('barbar ');
-> 'barbar'
This function is multi-byte safe.
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
str with all remstr prefixes and/or suffixes
removed. If none of the specifiers BOTH, LEADING or
TRAILING are given, BOTH is assumed. If remstr is not
specified, spaces are removed:
mysql> select TRIM(' bar ');
-> 'bar'
mysql> select TRIM(LEADING 'x' FROM 'xxxbarxxx');
-> 'barxxx'
mysql> select TRIM(BOTH 'x' FROM 'xxxbarxxx');
-> 'bar'
mysql> select TRIM(TRAILING 'xyz' FROM 'barxxyz');
-> 'barx'
This function is multi-byte safe.
SOUNDEX(str)
str. Two strings that sound almost the
same should have identical soundex strings. A standard soundex string
is 4 characters long, but the SOUNDEX() function returns an
arbitrarily long string. You can use SUBSTRING() on the result to get
a standard soundex string. All non-alphanumeric characters are ignored
in the given string. All international alpha characters outside the A-Z range
are treated as vowels:
mysql> select SOUNDEX('Hello');
-> 'H400'
mysql> select SOUNDEX('Quadratically');
-> 'Q36324'
SPACE(N)
N space characters:
mysql> select SPACE(6);
-> ' '
REPLACE(str,from_str,to_str)
str with all all occurrences of the string
from_str replaced by the string to_str:
mysql> select REPLACE('www.mysql.com', 'w', 'Ww');
-> 'WwWwWw.mysql.com'
This function is multi-byte safe.
REPEAT(str,count)
str repeated count
times. If count <= 0, returns an empty string. Returns NULL if
str or count are NULL:
mysql> select REPEAT('MySQL', 3);
-> 'MySQLMySQLMySQL'
REVERSE(str)
str with the order of the characters reversed:
mysql> select REVERSE('abc');
-> 'cba'
This function is multi-byte safe.
INSERT(str,pos,len,newstr)
str, with the substring beginning at position
pos and len characters long replaced by the string
newstr:
mysql> select INSERT('Quadratic', 3, 4, 'What');
-> 'QuWhattic'
This function is multi-byte safe.
ELT(N,str1,str2,str3,...)
str1 if N = 1, str2 if N =
2, and so on. Returns NULL if N is less than 1
or greater than the number of arguments. ELT() is the complement of
FIELD():
mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo');
-> 'ej'
mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo');
-> 'foo'
FIELD(str,str1,str2,str3,...)
str in the str1, str2,
str3, ... list.
Returns 0 if str is not found.
FIELD() is the complement of ELT():
mysql> select FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 2
mysql> select FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
-> 0
FIND_IN_SET(str,strlist)
1 to N if the string str is in the list
strlist consisting of N substrings. A string list is a string
composed of substrings separated by `,' characters. If the first
argument is a constant string and the second is a column of type SET,
the FIND_IN_SET() function is optimized to use bit arithmetic!
Returns 0 if str is not in strlist or if strlist
is the empty string. Returns NULL if either argument is NULL.
This function will not work properly if the first argument contains a
`,':
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
-> 2
MAKE_SET(bits,str1,str2,...)
bits set. str1 corresponds to bit 0, str2 to bit 1,
etc. NULL strings in str1, str2, ...
are not appended to the result:
mysql> SELECT MAKE_SET(1,'a','b','c');
-> 'a'
mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
-> 'hello,world'
mysql> SELECT MAKE_SET(0,'a','b','c');
-> ''
EXPORT_SET(bits,on,off,[separator,[number_of_bits]])
mysql> select EXPORT_SET(5,'Y','N',',',4)
-> Y,N,Y,N
LCASE(str)
LOWER(str)
str with all characters changed to lowercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> select LCASE('QUADRATICALLY');
-> 'quadratically'
This function is multi-byte safe.
UCASE(str)
UPPER(str)
str with all characters changed to uppercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> select UCASE('Hej');
-> 'HEJ'
This function is multi-byte safe.
LOAD_FILE(file_name)
max_allowed_packet.
If the file doesn't exist or can't be read due to one of the above reasons,
the function returns NULL:
mysql> UPDATE table_name
SET blob_column=LOAD_FILE("/tmp/picture")
WHERE id=1;
If you are not using MySQL Version 3.23, you have to do the reading
of the file inside your application and create an INSERT statement
to update the database with the file information. One way to do this, if
you are using the MySQL++ library, can be found at
http://www.mysql.com/documentation/mysql++/mysql++-examples.html.
MySQL automatically converts numbers to strings as necessary, and vice-versa:
mysql> SELECT 1+"1";
-> 2
mysql> SELECT CONCAT(2,' test');
-> '2 test'
If you want to convert a number to a string explicitly, pass it as the
argument to CONCAT().
If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons.
See section 7.3.6 Date and Time Types for a description of the range of values each type has and the valid formats in which date and time values may be specified.
Here is an example that uses date functions. The query below selects
all records with a date_col value from within the last 30 days:
mysql> SELECT something FROM table
WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;
DAYOFWEEK(date)
date (1 = Sunday, 2 = Monday, ... 7 =
Saturday). These index values correspond to the ODBC standard:
mysql> select DAYOFWEEK('1998-02-03');
-> 3
WEEKDAY(date)
date (0 = Monday, 1 = Tuesday, ... 6 = Sunday):
mysql> select WEEKDAY('1997-10-04 22:23:00');
-> 5
mysql> select WEEKDAY('1997-11-05');
-> 2
DAYOFMONTH(date)
date, in the range 1 to
31:
mysql> select DAYOFMONTH('1998-02-03');
-> 3
DAYOFYEAR(date)
date, in the range 1 to
366:
mysql> select DAYOFYEAR('1998-02-03');
-> 34
MONTH(date)
date, in the range 1 to 12:
mysql> select MONTH('1998-02-03');
-> 2
DAYNAME(date)
date:
mysql> select DAYNAME("1998-02-05");
-> 'Thursday'
MONTHNAME(date)
date:
mysql> select MONTHNAME("1998-02-05");
-> 'February'
QUARTER(date)
date, in the range 1
to 4:
mysql> select QUARTER('98-04-01');
-> 2
WEEK(date)
WEEK(date,first)
date, in the range
0 to 53 (yes, there may be the beginnings of a week 53),
for locations where Sunday is the first day of the week. The
two-argument form of WEEK() allows you to specify whether the
week starts on Sunday or Monday. The week starts on Sunday if the
second argument is 0, on Monday if the second argument is
1:
mysql> select WEEK('1998-02-20');
-> 7
mysql> select WEEK('1998-02-20',0);
-> 7
mysql> select WEEK('1998-02-20',1);
-> 8
mysql> select WEEK('1998-12-31',1);
-> 53
YEAR(date)
date, in the range 1000 to 9999:
mysql> select YEAR('98-02-03');
-> 1998
YEARWEEK(date)
YEARWEEK(date,first)
WEEK(). Note that the year may be
different from the year in the date argument for the first and the last
week of the year:
mysql> select YEARWEEK('1987-01-01');
-> 198653
HOUR(time)
time, in the range 0 to 23:
mysql> select HOUR('10:05:03');
-> 10
MINUTE(time)
time, in the range 0 to 59:
mysql> select MINUTE('98-02-03 10:05:03');
-> 5
SECOND(time)
time, in the range 0 to 59:
mysql> select SECOND('10:05:03');
-> 3
PERIOD_ADD(P,N)
N months to period P (in the format YYMM or
YYYYMM). Returns a value in the format YYYYMM.
Note that the period argument P is not a date value:
mysql> select PERIOD_ADD(9801,2);
-> 199803
PERIOD_DIFF(P1,P2)
P1 and P2.
P1 and P2 should be in the format YYMM or YYYYMM.
Note that the period arguments P1 and P2 are not
date values:
mysql> select PERIOD_DIFF(9802,199703);
-> 11
DATE_ADD(date,INTERVAL expr type)
DATE_SUB(date,INTERVAL expr type)
ADDDATE(date,INTERVAL expr type)
SUBDATE(date,INTERVAL expr type)
ADDDATE() and SUBDATE() are synonyms for
DATE_ADD() and DATE_SUB().
In MySQL Version 3.23, you can use + and - instead of
DATE_ADD() and DATE_SUB() if the expression on the right side is
a date or datetime column. (See example)
date is a DATETIME or DATE value specifying the starting
date. expr is an expression specifying the interval value to be added
or substracted from the starting date. expr is a string; it may start
with a `-' for negative intervals. type is a keyword indicating
how the expression should be interpreted.
The EXTRACT(type FROM date) function returns the 'type'
interval from the date.
The following table shows how the type and expr arguments
are related:
type value | Expected expr format
|
SECOND | SECONDS
|
MINUTE | MINUTES
|
HOUR | HOURS
|
DAY | DAYS
|
MONTH | MONTHS
|
YEAR | YEARS
|
MINUTE_SECOND | "MINUTES:SECONDS"
|
HOUR_MINUTE | "HOURS:MINUTES"
|
DAY_HOUR | "DAYS HOURS"
|
YEAR_MONTH | "YEARS-MONTHS"
|
HOUR_SECOND | "HOURS:MINUTES:SECONDS"
|
DAY_MINUTE | "DAYS HOURS:MINUTES"
|
DAY_SECOND | "DAYS HOURS:MINUTES:SECONDS"
|
expr format.
Those shown in the table are the suggested delimiters. If the date
argument is a DATE value and your calculations involve only
YEAR, MONTH, and DAY parts (that is, no time parts), the
result is a DATE value. Otherwise the result is a DATETIME
value:
mysql> SELECT "1997-12-31 23:59:59" + INTERVAL 1 SECOND;
-> 1998-01-01 00:00:00
mysql> SELECT INTERVAL 1 DAY + "1997-12-31";
-> 1998-01-01
mysql> SELECT "1998-01-01" - INTERVAL 1 SECOND;
-> 1997-12-31 23:59:59
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL 1 SECOND);
-> 1998-01-01 00:00:00
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL 1 DAY);
-> 1998-01-01 23:59:59
mysql> SELECT DATE_ADD("1997-12-31 23:59:59",
INTERVAL "1:1" MINUTE_SECOND);
-> 1998-01-01 00:01:00
mysql> SELECT DATE_SUB("1998-01-01 00:00:00",
INTERVAL "1 1:1:1" DAY_SECOND);
-> 1997-12-30 22:58:59
mysql> SELECT DATE_ADD("1998-01-01 00:00:00",
INTERVAL "-1 10" DAY_HOUR);
-> 1997-12-30 14:00:00
mysql> SELECT DATE_SUB("1998-01-02", INTERVAL 31 DAY);
-> 1997-12-02
mysql> SELECT EXTRACT(YEAR FROM "1999-07-02");
-> 1999
mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03");
-> 199907
mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03");
-> 20102
If you specify an interval value that is too short (does not include all the
interval parts that would be expected from the type keyword),
MySQL assumes you have left out the leftmost parts of the interval
value. For example, if you specify a type of DAY_SECOND, the
value of expr is expected to have days, hours, minutes, and seconds
parts. If you specify a value like "1:10", MySQL assumes
that the days and hours parts are missing and the value represents minutes
and seconds. In other words, "1:10" DAY_SECOND is interpreted in such
a way that it is equivalent to "1:10" MINUTE_SECOND. This is
analogous to the way that MySQL interprets TIME values
as representing elapsed time rather than as time of day.
Note that if you add or subtract a date value against something that
contains a time part, the date value will be automatically converted to a
datetime value:
mysql> select date_add("1999-01-01", interval 1 day);
-> 1999-01-02
mysql> select date_add("1999-01-01", interval 1 hour);
-> 1999-01-01 01:00:00
If you use really incorrect dates, the result is NULL. If you add
MONTH, YEAR_MONTH, or YEAR and the resulting date
has a day that is larger than the maximum day for the new month, the day is
adjusted to the maximum days in the new month:
mysql> select DATE_ADD('1998-01-30', Interval 1 month);
-> 1998-02-28
Note from the preceding example that the word INTERVAL and the
type keyword are not case sensitive.
TO_DAYS(date)
date, returns a daynumber (the number of days since year
0):
mysql> select TO_DAYS(950501);
-> 728779
mysql> select TO_DAYS('1997-10-07');
-> 729669
TO_DAYS() is not intended for use with values that precede the advent
of the Gregorian calendar (1582), because it doesn't take into account the
days that were lost when the calender was changed.
FROM_DAYS(N)
N, returns a DATE value:
mysql> select FROM_DAYS(729669);
-> '1997-10-07'
FROM_DAYS() is not intended for use with values that precede the
advent of the Gregorian calendar (1582), because it doesn't take into account
the days that were lost when the calender was changed.
DATE_FORMAT(date,format)
date value according to the format string. The
following specifiers may be used in the format string:
%M | Month name (January..December)
|
%W | Weekday name (Sunday..Saturday)
|
%D | Day of the month with English suffix (1st, 2nd, 3rd, etc.)
|
%Y | Year, numeric, 4 digits |
%y | Year, numeric, 2 digits |
%X | Year for the week where Sunday is the first day of the week, numeric, 4 digits, used with '%V' |
%x | Year for the week, where Monday is the first day of the week, numeric, 4 digits, used with '%v' |
%a | Abbreviated weekday name (Sun..Sat)
|
%d | Day of the month, numeric (00..31)
|
%e | Day of the month, numeric (0..31)
|
%m | Month, numeric (01..12)
|
%c | Month, numeric (1..12)
|
%b | Abbreviated month name (Jan..Dec)
|
%j | Day of year (001..366)
|
%H | Hour (00..23)
|
%k | Hour (0..23)
|
%h | Hour (01..12)
|
%I | Hour (01..12)
|
%l | Hour (1..12)
|
%i | Minutes, numeric (00..59)
|
%r | Time, 12-hour (hh:mm:ss [AP]M)
|
%T | Time, 24-hour (hh:mm:ss)
|
%S | Seconds (00..59)
|
%s | Seconds (00..59)
|
%p | AM or PM
|
%w | Day of the week (0=Sunday..6=Saturday)
|
%U | Week (0..53), where Sunday is the first day of the week
|
%u | Week (0..53), where Monday is the first day of the week
|
%V | Week (1..53), where Sunday is the first day of the week. Used with '%X'
|
%v | Week (1..53), where Monday is the first day of the week. Used with '%x'
|
%% | A literal `%'. |
mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y');
-> 'Saturday October 1997'
mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s');
-> '22:23:00'
mysql> select DATE_FORMAT('1997-10-04 22:23:00',
'%D %y %a %d %m %b %j');
-> '4th 97 Sat 04 10 Oct 277'
mysql> select DATE_FORMAT('1997-10-04 22:23:00',
'%H %k %I %r %T %S %w');
-> '22 22 10 10:23:00 PM 22:23:00 00 6'
mysql> select DATE_FORMAT('1999-01-01', '%X %V');
-> '1998 52'
As of MySQL Version 3.23, the `%' character is required before
format specifier characters. In earlier versions of MySQL,
`%' was optional.
TIME_FORMAT(time,format)
DATE_FORMAT() function above, but the
format string may contain only those format specifiers that handle
hours, minutes, and seconds. Other specifiers produce a NULL value or
0.
CURDATE()
CURRENT_DATE
'YYYY-MM-DD' or YYYYMMDD
format, depending on whether the function is used in a string or numeric
context:
mysql> select CURDATE();
-> '1997-12-15'
mysql> select CURDATE() + 0;
-> 19971215
CURTIME()
CURRENT_TIME
'HH:MM:SS' or HHMMSS
format, depending on whether the function is used in a string or numeric
context:
mysql> select CURTIME();
-> '23:50:26'
mysql> select CURTIME() + 0;
-> 235026
NOW()
SYSDATE()
CURRENT_TIMESTAMP
'YYYY-MM-DD HH:MM:SS'
or YYYYMMDDHHMMSS format, depending on whether the function is used in
a string or numeric context:
mysql> select NOW();
-> '1997-12-15 23:50:26'
mysql> select NOW() + 0;
-> 19971215235026
UNIX_TIMESTAMP()
UNIX_TIMESTAMP(date)
'1970-01-01 00:00:00' GMT). If UNIX_TIMESTAMP() is called with
a date argument, it returns the value of the argument as seconds since
'1970-01-01 00:00:00' GMT. date may be a DATE string,
a DATETIME string, a TIMESTAMP, or a number in the format
YYMMDD or YYYYMMDD in local time:
mysql> select UNIX_TIMESTAMP();
-> 882226357
mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00');
-> 875996580
When UNIX_TIMESTAMP is used on a TIMESTAMP column, the function
will receive the value directly, with no implicit
``string-to-unix-timestamp'' conversion.
If you give UNIX_TIMESTAMP() a wrong or out-of-range date, it will
return 0.
FROM_UNIXTIME(unix_timestamp)
unix_timestamp argument as a value in
'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on
whether the function is used in a string or numeric context:
mysql> select FROM_UNIXTIME(875996580);
-> '1997-10-04 22:23:00'
mysql> select FROM_UNIXTIME(875996580) + 0;
-> 19971004222300
FROM_UNIXTIME(unix_timestamp,format)
format string. format may contain the same specifiers as
those listed in the entry for the DATE_FORMAT() function:
mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(),
'%Y %D %M %h:%i:%s %x');
-> '1997 23rd December 03:43:30 x'
SEC_TO_TIME(seconds)
seconds argument, converted to hours, minutes, and seconds,
as a value in 'HH:MM:SS' or HHMMSS format, depending on whether
the function is used in a string or numeric context:
mysql> select SEC_TO_TIME(2378);
-> '00:39:38'
mysql> select SEC_TO_TIME(2378) + 0;
-> 3938
TIME_TO_SEC(time)
time argument, converted to seconds:
mysql> select TIME_TO_SEC('22:23:00');
-> 80580
mysql> select TIME_TO_SEC('00:39:38');
-> 2378
DATABASE()
mysql> select DATABASE();
-> 'test'
If there is no current database, DATABASE() returns the empty string.
USER()
SYSTEM_USER()
SESSION_USER()
mysql> select USER();
-> 'davida@localhost'
In MySQL Version 3.22.11 or later, this includes the client hostname
as well as the user name. You can extract just the user name part like this
(which works whether or not the value includes a hostname part):
mysql> select substring_index(USER(),"@",1);
-> 'davida'
PASSWORD(str)
str. This is
the function that is used for encrypting MySQL passwords for storage
in the Password column of the user grant table:
mysql> select PASSWORD('badpwd');
-> '7f84554057dd964b'
PASSWORD() encryption is non-reversible.
PASSWORD() does not perform password encryption in the same way that
Unix passwords are encrypted. You should not assume that if your Unix
password and your MySQL password are the same, PASSWORD()
will result in the same encrypted value as is stored in the Unix password
file. See ENCRYPT().
ENCRYPT(str[,salt])
str using the Unix crypt() system call. The
salt argument should be a string with two characters.
(As of MySQL Version 3.22.16, salt may be longer than two characters.):
mysql> select ENCRYPT("hello");
-> 'VxuFAJXVARROc'
If crypt() is not available on your system, ENCRYPT() always
returns NULL.
ENCRYPT() ignores all but the first 8 characters of str, at
least on some systems. This will be determined by the behavior of the
underlying crypt() system call.
ENCODE(str,pass_str)
str using pass_str as the password.
To decrypt the result, use DECODE().
The results is a binary string of the same length as string.
If you want to save it in a column, use a BLOB column type.
DECODE(crypt_str,pass_str)
crypt_str using pass_str as the
password. crypt_str should be a string returned from
ENCODE().
MD5(string)
mysql> select MD5("testing")
-> 'ae2b1fca515949e5d54fb22b8ed95575'
This is an "RSA Data Security, Inc. MD5 Message-Digest Algorithm".
LAST_INSERT_ID([expr])
AUTO_INCREMENT column.
See section 22.4.30 mysql_insert_id().
mysql> select LAST_INSERT_ID();
-> 195
The last ID that was generated is maintained in the server on a
per-connection basis. It will not be changed by another client. It will not
even be changed if you update another AUTO_INCREMENT column with a
non-magic value (that is, a value that is not NULL and not 0).
If expr is given as an argument to LAST_INSERT_ID() in an
UPDATE clause, then the value of the argument is returned as a
LAST_INSERT_ID() value. This can be used to simulate sequences.
First create the table:
mysql> create table sequence (id int not null); mysql> insert into sequence values (0);Then the table can be used to generate sequence numbers like this:
mysql> update sequence set id=LAST_INSERT_ID(id+1);You can generate sequences without calling
LAST_INSERT_ID(), but the
utility of using the function this way is that the ID value is maintained in
the server as the last automatically generated value. You can retrieve the
new ID as you would read any normal AUTO_INCREMENT value in
MySQL. For example, LAST_INSERT_ID() (without an argument)
will return the new ID. The C API function mysql_insert_id()
can also be used to get the value.
FORMAT(X,D)
X to a format like '#,###,###.##', rounded
to D decimals. If D is 0, the result will have no
decimal point or fractional part:
mysql> select FORMAT(12332.123456, 4);
-> '12,332.1235'
mysql> select FORMAT(12332.1,4);
-> '12,332.1000'
mysql> select FORMAT(12332.2,0);
-> '12,332'
VERSION()
mysql> select VERSION();
-> '3.23.13-log'
Note that if your version ends with -log this means that logging is
enabled.
CONNECTION_ID()
thread_id) for the connection.
Every connection has its own unique id:
mysql> select CONNECTION_ID();
-> 1
GET_LOCK(str,timeout)
str, with a
timeout of timeout seconds. Returns 1 if the lock was obtained
successfully, 0 if the attempt timed out, or NULL if an error
occurred (such as running out of memory or the thread was killed with
mysqladmin kill). A lock is released when you execute
RELEASE_LOCK(), execute a new GET_LOCK(), or the thread
terminates. This function can be used to implement application locks or to
simulate record locks. It blocks requests by other clients for locks with
the same name; clients that agree on a given lock string name can use the
string to perform cooperative advisory locking:
mysql> select GET_LOCK("lock1",10);
-> 1
mysql> select GET_LOCK("lock2",10);
-> 1
mysql> select RELEASE_LOCK("lock2");
-> 1
mysql> select RELEASE_LOCK("lock1");
-> NULL
Note that the second RELEASE_LOCK() call returns NULL because
the lock "lock1" was automatically released by the second
GET_LOCK() call.
RELEASE_LOCK(str)
str that was obtained with
GET_LOCK(). Returns 1 if the lock was released, 0 if the
lock wasn't locked by this thread (in which case the lock is not released),
and NULL if the named lock didn't exist. The lock will not exist if
it was never obtained by a call to GET_LOCK() or if it already has
been released.
BENCHMARK(count,expr)
BENCHMARK() function executes the expression expr
repeatedly count times. It may be used to time how fast MySQL
processes the expression. The result value is always 0. The intended
use is in the mysql client, which reports query execution times:
mysql> select BENCHMARK(1000000,encode("hello","goodbye"));
+----------------------------------------------+
| BENCHMARK(1000000,encode("hello","goodbye")) |
+----------------------------------------------+
| 0 |
+----------------------------------------------+
1 row in set (4.74 sec)
The time reported is elapsed time on the client end, not CPU time on the
server end. It may be advisable to execute BENCHMARK() several
times, and interpret the result with regard to how heavily loaded the
server machine is.
INET_NTOA(expr)
mysql> select INET_NTOA(3520061480);
-> "209.207.224.40"
INET_ATON(expr)
mysql> select INET_ATON("209.207.224.40");
-> 3520061480
GROUP BY Clauses
If you use a group function in a statement containing no GROUP BY
clause, it is equivalent to grouping on all rows.
COUNT(expr)
NULL values in the rows
retrieved by a SELECT statement:
mysql> select student.student_name,COUNT(*)
from student,course
where student.student_id=course.student_id
GROUP BY student_name;
COUNT(*) is somewhat different in that it returns a count of
the number of rows retrieved, whether or not they contain NULL
values.
COUNT(*) is optimized to
return very quickly if the SELECT retrieves from one table, no
other columns are retrieved, and there is no WHERE clause.
For example:
mysql> select COUNT(*) from student;
COUNT(DISTINCT expr,[expr...])
NULL values:
mysql> select COUNT(DISTINCT results) from student;In MySQL you can get the number of distinct expression combinations that don't contain NULL by giving a list of expressions. In ANSI SQL you would have to do a concatenation of all expressions inside
CODE(DISTINCT ..).
AVG(expr)
expr:
mysql> select student_name, AVG(test_score)
from student
GROUP BY student_name;
MIN(expr)
MAX(expr)
expr. MIN() and
MAX() may take a string argument; in such cases they return the
minimum or maximum string value. See section 12.4 How MySQL Uses Indexes.
mysql> select student_name, MIN(test_score), MAX(test_score)
from student
GROUP BY student_name;
SUM(expr)
expr. Note that if the return set has no rows,
it returns NULL!
STD(expr)
STDDEV(expr)
expr. This is an extension to
ANSI SQL. The STDDEV() form of this function is provided for Oracle
compatability.
BIT_OR(expr)
OR of all bits in expr. The calculation is
performed with 64-bit (BIGINT) precision.
BIT_AND(expr)
AND of all bits in expr. The calculation is
performed with 64-bit (BIGINT) precision.
MySQL has extended the use of GROUP BY. You can use columns or
calculations in the SELECT expressions that don't appear in
the GROUP BY part. This stands for any possible value for this
group. You can use this to get better performance by avoiding sorting and
grouping on unnecessary items. For example, you don't need to group on
customer.name in the following query:
mysql> select order.custid,customer.name,max(payments)
from order,customer
where order.custid = customer.custid
GROUP BY order.custid;
In ANSI SQL, you would have to add customer.name to the GROUP
BY clause. In MySQL, the name is redundant if you don't run in
ANSI mode.
Don't use this feature if the columns you omit from the GROUP BY part
aren't unique in the group!
In some cases, you can use MIN() and MAX() to obtain a specific
column value even if it isn't unique. The following gives the value of
column from the row containing the smallest value in the sort
column:
substr(MIN(concat(sort,space(6-length(sort)),column),7,length(column)))
Note that if you are using MySQL Version 3.22 (or earlier) or if
you are trying to follow ANSI SQL, you can't use expressions in GROUP
BY or ORDER BY clauses. You can work around this limitation by
using an alias for the expression:
mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name
GROUP BY id,val ORDER BY val;
In MySQL Version 3.23 you can do:
mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND();
CREATE DATABASE SyntaxCREATE DATABASE [IF NOT EXISTS] db_name
CREATE DATABASE creates a database with the given name. Rules for
allowable database names are given in section 7.1.5 Database, Table, Index, Column, and Alias Names. An error occurs if
the database already exists and you didn't specify IF NOT EXISTS.
Databases in MySQL are implemented as directories containing files
that correspond to tables in the database. Because there are no tables in a
database when it is initially created, the CREATE DATABASE statement
only creates a directory under the MySQL data directory.
You can also create databases with mysqladmin.
See section 14.1 Overview of the Different MySQL Programs.
DROP DATABASE SyntaxDROP DATABASE [IF EXISTS] db_name
DROP DATABASE drops all tables in the database and deletes the
database. If you do a DROP DATABASE on a symbolic linked
database, both the link and the original database is deleted. Be
VERY careful with this command!
DROP DATABASE returns the number of files that were removed from
the database directory. Normally, this is three times the number of
tables, because normally each table corresponds to a `.MYD' file, a
`.MYI' file, and a `.frm' file.
The DROP DATABASE command removes from the given database
directory all files with the following extensions:
| .BAK | .DAT | .HSH | .ISD |
| .ISM | .ISM | .MRG | .MYD |
| .MYI | .db | .frm |
All subdirectories that consists of 2 digits (RAID directories)
are also removed.
In MySQL Version 3.22 or later, you can use the keywords
IF EXISTS to prevent an error from occurring if the database doesn't
exist.
You can also drop databases with mysqladmin. See section 14.1 Overview of the Different MySQL Programs.
CREATE TABLE Syntax
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)]
[table_options] [select_statement]
create_definition:
col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT]
[PRIMARY KEY] [reference_definition]
or PRIMARY KEY (index_col_name,...)
or KEY [index_name] (index_col_name,...)
or INDEX [index_name] (index_col_name,...)
or UNIQUE [INDEX] [index_name] (index_col_name,...)
or FULLTEXT [INDEX] [index_name] (index_col_name,...)
or [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...)
[reference_definition]
or CHECK (expr)
type:
TINYINT[(length)] [UNSIGNED] [ZEROFILL]
or SMALLINT[(length)] [UNSIGNED] [ZEROFILL]
or MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL]
or INT[(length)] [UNSIGNED] [ZEROFILL]
or INTEGER[(length)] [UNSIGNED] [ZEROFILL]
or BIGINT[(length)] [UNSIGNED] [ZEROFILL]
or REAL[(length,decimals)] [UNSIGNED] [ZEROFILL]
or DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL]
or FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL]
or DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL]
or NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL]
or CHAR(length) [BINARY]
or VARCHAR(length) [BINARY]
or DATE
or TIME
or TIMESTAMP
or DATETIME
or TINYBLOB
or BLOB
or MEDIUMBLOB
or LONGBLOB
or TINYTEXT
or TEXT
or MEDIUMTEXT
or LONGTEXT
or ENUM(value1,value2,value3,...)
or SET(value1,value2,value3,...)
index_col_name:
col_name [(length)]
reference_definition:
REFERENCES tbl_name [(index_col_name,...)]
[MATCH FULL | MATCH PARTIAL]
[ON DELETE reference_option]
[ON UPDATE reference_option]
reference_option:
RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT
table_options:
TYPE = {ISAM | MYISAM | HEAP | MERGE}
or AUTO_INCREMENT = #
or AVG_ROW_LENGTH = #
or CHECKSUM = {0 | 1}
or COMMENT = "string"
or MAX_ROWS = #
or MIN_ROWS = #
or PACK_KEYS = {0 | 1}
or PASSWORD = "string"
or DELAY_KEY_WRITE = {0 | 1}
or ROW_FORMAT= { default | dynamic | static | compressed }
or RAID_TYPE= {1 | STRIPED | RAID0 } RAID_CHUNKS=# RAID_CHUNKSIZE=#;
or UNION = (table_name,[table_name...])
select_statement:
[IGNORE | REPLACE] SELECT ... (Some legal select statement)
CREATE TABLE
creates a table with the given name in the current database. Rules for
allowable table names are given in section 7.1.5 Database, Table, Index, Column, and Alias Names. An error occurs if
there is no current database or if the table already exists.
In MySQL Version 3.22 or later, the table name can be specified as
db_name.tbl_name. This works whether or not there is a current
database.
In MySQL Version 3.23, you can use the TEMPORARY keyword when
you create a table. A temporary table will automatically be deleted if a
connection dies and the name is per connection. This means that two different
connections can both use the same temporary table name without conflicting
with each other or with an existing table of the same name. (The existing table
is hidden until the temporary table is deleted).
In MySQL Version 3.23 or later, you can use the keywords
IF NOT EXISTS so that an error does not occur if the table already
exists. Note that there is no verification that the table structures are
identical.
Each table tbl_name is represented by some files in the database
directory. In the case of MyISAM-type tables you will get:
| File | Purpose |
tbl_name.frm | Table definition (form) file |
tbl_name.MYD | Data file |
tbl_name.MYI | Index file |
For more information on the properties of the various column types, see section 7.3 Column Types:
NULL nor NOT NULL is specified, the column
is treated as though NULL had been specified.
AUTO_INCREMENT.
When you insert a value of NULL (recommended) or 0 into an
AUTO_INCREMENT column, the column is set to value+1, where
value is the largest value for the column currently in the table.
AUTO_INCREMENT sequences begin with 1.
See section 22.4.30 mysql_insert_id().
If you delete the row containing the maximum value for an
AUTO_INCREMENT column, the value will be reused with an ISAM
table but not with a MyISAM table. If you delete all rows in the
table with DELETE FROM table_name (without a WHERE) in
AUTOCOMMIT mode, the sequence starts over for both table types.
NOTE: There can be only one AUTO_INCREMENT column per
table, and it must be indexed. MySQL Version 3.23 will also only
work properly if the auto_increment column only has positive
values. Inserting a negative number is regarded as inserting a very large
positive number. This is done to avoid precision problems when
numbers 'wrap' over from positive to negative and also to ensure that one
doesn't accidently get an auto_increment column that contains 0.
To make MySQL compatible with some ODBC applications, you can find
the last inserted row with the following query:
SELECT * FROM tbl_name WHERE auto_col IS NULL
NULL values are handled differently for TIMESTAMP columns than
for other column types. You cannot store a literal NULL in a
TIMESTAMP column; setting the column to NULL sets it to the
current date and time. Because TIMESTAMP columns behave this way, the
NULL and NOT NULL attributes do not apply in the normal way and
are ignored if you specify them.
On the other hand, to make it easier for MySQL clients to use
TIMESTAMP columns, the server reports that such columns may be
assigned NULL values (which is true), even though TIMESTAMP
never actually will contain a NULL value. You can see this when you
use DESCRIBE tbl_name to get a description of your table.
Note that setting a TIMESTAMP column to 0 is not the same
as setting it to NULL, because 0 is a valid TIMESTAMP
value.
DEFAULT value is specified for a column, MySQL
automatically assigns one.
If the column may take NULL as a value, the default value is
NULL.
If the column is declared as NOT NULL, the default value depends on
the column type:
AUTO_INCREMENT
attribute, the default is 0. For an AUTO_INCREMENT column, the
default value is the next value in the sequence.
TIMESTAMP, the default is the
appropriate zero value for the type. For the first TIMESTAMP
column in a table, the default value is the current date and time.
See section 7.3.6 Date and Time Types.
ENUM, the default value is the empty string.
For ENUM, the default is the first enumeration value.
NOW() or CURRENT_DATE.
KEY is a synonym for INDEX.
UNIQUE key can have only distinct values. An
error occurs if you try to add a new row with a key that matches an existing
row.
PRIMARY KEY is a unique KEY with the extra constraint
that all key columns must be defined as NOT NULL. In MySQL
the key is named PRIMARY. A table can have only one PRIMARY KEY.
If you don't have a PRIMARY KEY and some applications ask for the
PRIMARY KEY in your tables, MySQL will return the first
UNIQUE key, which doesn't have any NULL columns, as the
PRIMARY KEY.
PRIMARY KEY can be a multiple-column index. However, you cannot
create a multiple-column index using the PRIMARY KEY key attibute in a
column specification. Doing so will mark only that single column as primary.
You must use the PRIMARY KEY(index_col_name, ...) syntax.
PRIMARY or UNIQUE key consists of only one column and this
is of type integer, you can also refer to it as _rowid
(new in Version 3.23.11).
index_col_name, with an optional suffix (_2,
_3, ...) to make it unique. You can see index names for a
table using SHOW INDEX FROM tbl_name.
See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
MyISAM table type supports indexes on columns that can have
NULL values. In other cases you must declare such columns
NOT NULL or an error results.
col_name(length) syntax, you can specify an index that
uses only a part of a CHAR or VARCHAR column. This can
make the index file much smaller.
See section 7.3.9 Column Indexes.
MyISAM table type supports indexing on BLOB and
TEXT columns. When putting an index on a BLOB or TEXT
column you MUST always specify the length of the index:
CREATE TABLE test (blob_col BLOB, index(blob_col(10)));
ORDER BY or GROUP BY with a TEXT or
BLOB column, only the first max_sort_length bytes are used.
See section 7.3.7.2 The BLOB and TEXT Types.
MyISAM table type supports FULLTEXT indexes. They can be created
only from VARCHAR and TEXT columns.
Indexing always happens over the entire column, partial indexing is not
supported. See section 24.2 MySQL Full-text Search for details of operation.
FOREIGN KEY, CHECK, and REFERENCES clauses don't
actually do anything. The syntax for them is provided only for compatibility,
to make it easier to port code from other SQL servers and to run applications
that create tables with references.
See section 5.4 Functionality Missing from MySQL.
NULL column takes one bit extra, rounded up to the nearest byte.
row length = 1
+ (sum of column lengths)
+ (number of NULL columns + 7)/8
+ (number of variable-length columns)
table_options and SELECT options are only
implemented in MySQL Version 3.23 and above.
The different table types are:
| BDB or Berkeley_db | Transaction-safe tables See section 8.5 BDB or Berkeley_db Tables. |
| HEAP | The data for this table is only stored in memory. See section 8.4 HEAP Tables. |
| ISAM | The original table handler. See section 8.3 ISAM Tables. |
| MERGE | A collection of MyISAM tables used as one table. See section 8.2 MERGE Tables. |
| MyISAM | The new binary portable table handler. See section 8.1 MyISAM Tables. |
AUTO_INCREMENT | The next auto_increment value you want to set for your table (MyISAM). |
AVG_ROW_LENGTH | An approximation of the average row length for your table. You only need to set this for large tables with variable size records. |
CHECKSUM | Set this to 1 if you want MySQL to maintain a checksum for all rows (makes the table a little slower to update but makes it easier to find corrupted tables) (MyISAM). |
COMMENT | A 60-character comment for your table. |
MAX_ROWS | Max number of rows you plan to store in the table. |
MIN_ROWS | Minimum number of rows you plan to store in the table. |
PACK_KEYS | Set this to 1 if you want to have a smaller index. This usually makes updates slower and reads faster (MyISAM, ISAM). |
PASSWORD | Encrypt the .frm file with a password. This option doesn't do anything in the standard MySQL version.
|
DELAY_KEY_WRITE | Set this to 1 if want to delay key table updates until the table is closed (MyISAM). |
ROW_FORMAT | Defines how the rows should be stored (for the future). |
MyISAM table, MySQL uses the product of
max_rows * avg_row_length to decide how big the resulting table
will be. If you don't specify any of the above options, the maximum size
for a table will be 4G (or 2G if your operating systems only supports 2G
tables). The reason for this is just to keep down the pointer sizes
to make the index smaller and faster if you don't really need big files.
If you don't use PACK_KEYS, the default is to only pack strings,
not numbers. If you use PACK_KEYS=1, numbers will be packed as well.
When packing binary number keys, MySQL will use prefix compression.
This means that you will only get a big benefit of this if you have
many numbers that are the same. Prefix compression means that every
key needs one extra byte to indicate how many bytes of the previous key are
the same for the next key (note that the pointer to the row is stored
in high-byte-first-order directly after the key, to improve
compression.) This means that if you have many equal keys on two rows
in a row, all following 'same' keys will usually only take 2 bytes
(including the pointer to the row). Compare this to the ordinary case
where the following keys will take storage_size_for_key +
pointer_size (usually 4). On the other hand, if all keys are
totally different, you will lose 1 byte per key, if the key isn't a
key that can have NULL values (In this case the packed key length will
be stored in the same byte that is used to mark if a key is NULL.)
SELECT after the CREATE STATEMENT,
MySQL will create new fields for all elements in the
SELECT. For example:
mysql> CREATE TABLE test (a int not null auto_increment,
primary key (a), key(b))
TYPE=HEAP SELECT b,c from test2;
This will create a HEAP table with 3 columns. Note that the table will
automatically be deleted if any errors occur while copying data
into the table.
RAID_TYPE option will help you to break the 2G/4G limit for
the MyISAM data file (not the index file) on
operating systems that don't support big files. You can get also more speed
from the I/O bottleneck by putting RAID directories on different
physical disks. RAID_TYPE will work on any OS, as long as you have
configured MySQL with --with-raid. For now the only allowed
RAID_TYPE is STRIPED (1 and RAID0 are aliases
for this).
If you specify RAID_TYPE=STRIPED for a MyISAM table,
MyISAM will create RAID_CHUNKS subdirectories named 00,
01, 02 in the database directory. In each of these directories
MyISAM will create a table_name.MYD. When writing data
to the data file, the RAID handler will map the first
RAID_CHUNKSIZE *1024 bytes to the first file, the next
RAID_CHUNKSIZE *1024 bytes to the next file and so on.
UNION is used when you want to use a collection of identical
tables as one. This only works with MERGE tables. See section 8.2 MERGE Tables.
For the moment you need to have SELECT, UPDATE, and
DELETE privileges on the tables you map to a MERGE table.
All mapped tables must be in the same database as the MERGE table.
PRIMARY key will be placed first, followed
by all UNIQUE keys and then the normal keys. This helps the
MySQL optimizer to prioritize which key to use and also more quickly
detect duplicated UNIQUE keys.
In some cases, MySQL silently changes a column specification from
that given in a CREATE TABLE statement. (This may also occur with
ALTER TABLE.):
VARCHAR columns with a length less than four are changed to
CHAR.
VARCHAR, TEXT, or BLOB),
all CHAR columns longer than three characters are changed to
VARCHAR columns. This doesn't affect how you use the columns in
any way; in MySQL, VARCHAR is just a different way to
store characters. MySQL performs this conversion because it
saves space and makes table operations faster. See section 8 MySQL Table Types.
TIMESTAMP display sizes must be even and in the range from 2 to 14.
If you specify a display size of 0 or greater than 14, the size is coerced
to 14. Odd-valued sizes in the range from 1 to 13 are coerced
to the next higher even number.
NULL in a TIMESTAMP column; setting
it to NULL sets it to the current date and time. Because
TIMESTAMP columns behave this way, the NULL and NOT NULL
attributes do not apply in the normal way and are ignored if you specify
them. DESCRIBE tbl_name always reports that a TIMESTAMP
column may be assigned NULL values.
If you want to see whether or not MySQL used a column type other
than the one you specified, issue a DESCRIBE tbl_name statement after
creating or altering your table.
Certain other column type changes may occur if you compress a table
using myisampack. See section 8.1.2.3 Compressed Table Characteristics.
ALTER TABLE Syntax
ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...]
alter_specification:
ADD [COLUMN] create_definition [FIRST | AFTER column_name ]
or ADD [COLUMN] (create_definition, create_definition,...)
or ADD INDEX [index_name] (index_col_name,...)
or ADD PRIMARY KEY (index_col_name,...)
or ADD UNIQUE [index_name] (index_col_name,...)
or ADD FULLTEXT [index_name] (index_col_name,...)
or ADD [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...)
[reference_definition]
or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
or CHANGE [COLUMN] old_col_name create_definition
or MODIFY [COLUMN] create_definition
or DROP [COLUMN] col_name
or DROP PRIMARY KEY
or DROP INDEX index_name
or RENAME [TO] new_tbl_name
or ORDER BY col
or table_options
ALTER TABLE allows you to change the structure of an existing table.
For example, you can add or delete columns, create or destroy indexes, change
the type of existing columns, or rename columns or the table itself. You can
also change the comment for the table and type of the table.
See section 7.7 CREATE TABLE Syntax.
If you use ALTER TABLE to change a column specification but
DESCRIBE tbl_name indicates that your column was not changed, it is
possible that MySQL ignored your modification for one of the reasons
described in section 7.7.1 Silent Column Specification Changes. For example, if you try to change
a VARCHAR column to CHAR, MySQL will still use
VARCHAR if the table contains other variable-length columns.
ALTER TABLE works by making a temporary copy of the original table.
The alteration is performed on the copy, then the original table is
deleted and the new one is renamed. This is done in such a way that
all updates are automatically redirected to the new table without
any failed updates. While ALTER TABLE is executing, the original
table is readable by other clients. Updates and writes to the table
are stalled until the new table is ready:
ALTER TABLE, you need select, insert,
delete, update, create, and drop
privileges on the table.
IGNORE is a MySQL extension to ANSI SQL92.
It controls how ALTER TABLE works if there are duplicates on
unique keys in the new table.
If IGNORE isn't specified, the copy is aborted and rolled back.
If IGNORE is specified, then for rows with duplicates on a unique
key, only the first row is used; the others are deleted.
ADD, ALTER, DROP, and
CHANGE clauses in a single ALTER TABLE statement. This is a
MySQL extension to ANSI SQL92, which allows only one of each clause
per ALTER TABLE statement.
CHANGE col_name, DROP col_name, and DROP
INDEX are MySQL extensions to ANSI SQL92.
MODIFY is an Oracle extension to ALTER TABLE.
TRUNCATE is an Oracle extension. See section 7.18 TRUNCATE Syntax.
COLUMN is a pure noise word and can be omitted.
ALTER TABLE tbl_name RENAME TO new_name without any other
options, MySQL simply renames the files that correspond to the table
tbl_name. There is no need to create the temporary table.
See section 7.9 RENAME TABLE Syntax.
create_definition clauses use the same syntax for ADD and
CHANGE as for CREATE TABLE. Note that this syntax includes
the column name, not just the column type.
See section 7.7 CREATE TABLE Syntax.
CHANGE old_col_name create_definition
clause. To do so, specify the old and new column names and the type that
the column currently has. For example, to rename an INTEGER column
from a to b, you can do this:
mysql> ALTER TABLE t1 CHANGE a b INTEGER;If you want to change a column's type but not the name,
CHANGE
syntax still requires two column names even if they are the same. For
example:
mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL;However, as of MySQL Version 3.22.16a, you can also use
MODIFY
to change a column's type without renaming it:
mysql> ALTER TABLE t1 MODIFY b BIGINT NOT NULL;
CHANGE or MODIFY to shorten a column for which
an index exists on part of the column (for instance, if you have an index
on the first 10 characters of a VARCHAR column), you cannot make
the column shorter than the number of characters that are indexed.
CHANGE or MODIFY,
MySQL tries to convert data to the new type as well as possible.
FIRST or
ADD ... AFTER col_name to add a column at a specific position within
a table row. The default is to add the column last.
ALTER COLUMN specifies a new default value for a column
or removes the old default value.
If the old default is removed and the column can be NULL, the new
default is NULL. If the column cannot be NULL, MySQL
assigns a default value.
Default value assignment is described in
section 7.7 CREATE TABLE Syntax.
DROP INDEX removes an index. This is a MySQL extension to
ANSI SQL92.
DROP PRIMARY KEY drops the primary index. If no such
index exists, it drops the first UNIQUE index in the table.
(MySQL marks the first UNIQUE key as the PRIMARY KEY
if no PRIMARY KEY was specified explicitly.)
ORDER BY allows you to create the new table with the rows in a
specific order. Note that the table will not remain in this order after
inserts and deletes. In some cases, it may make sorting easier for
MySQL if the table is in order by the column that you wish to
order it by later. This option is mainly useful when you know that you
are mostly going to query the rows in a certain order; By using this
option after big changes to the table, you may be able to get higher
performance.
ALTER TABLE on a MyISAM table, all non-unique
indexes are created in a separate batch (like in REPAIR).
This should make ALTER TABLE much faster when you have many indexes.
mysql_info(), you can find out how many
records were copied, and (when IGNORE is used) how many records were
deleted due to duplication of unique key values.
FOREIGN KEY, CHECK, and REFERENCES clauses don't
actually do anything. The syntax for them is provided only for compatibility,
to make it easier to port code from other SQL servers and to run applications
that create tables with references.
See section 5.4 Functionality Missing from MySQL.
Here is an example that shows some of the uses of ALTER TABLE. We
begin with a table t1 that is created as shown below:
mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10));
To rename the table from t1 to t2:
mysql> ALTER TABLE t1 RENAME t2;
To change column a from INTEGER to TINYINT NOT NULL
(leaving the name the same), and to change column b from
CHAR(10) to CHAR(20) as well as renaming it from b to
c:
mysql> ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20);
To add a new TIMESTAMP column named d:
mysql> ALTER TABLE t2 ADD d TIMESTAMP;
To add an index on column d, and make column a the primary key:
mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a);
To remove column c:
mysql> ALTER TABLE t2 DROP COLUMN c;
To add a new AUTO_INCREMENT integer column named c:
mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT,
ADD INDEX (c);
Note that we indexed c, because AUTO_INCREMENT columns must be
indexed, and also that we declare c as NOT NULL, because
indexed columns cannot be NULL.
When you add an AUTO_INCREMENT column, column values are filled in
with sequence numbers for you automatically. You can set the first
sequence number by executing SET INSERT_ID=# before
ALTER TABLE or using the AUTO_INCREMENT = # table option.
See section 7.33 SET Syntax.
See section 20.21 Problems with ALTER TABLE..
RENAME TABLE SyntaxRENAME TABLE tbl_name TO new_table_name[, tbl_name2 TO new_table_name2,...]
The rename is done atomically, which means that no other thread can access any of the tables while the rename is running. This makes it possible to replace a table with an empty one:
CREATE TABLE new_table (...); RENAME TABLE old_table TO backup_table, new_table TO old_table;
The rename is done from left to right, which means that if you want to swap two tables names, you have to:
RENAME TABLE old_table TO backup_table,
new_table TO old_table,
backup_table TO old_table;
As long as two databases are on the same disk you can also rename from one database to another:
RENAME TABLE current_database.table_name TO other_database.table_name;
When you execute RENAME, you can't have any locked tables or
active transactions. You must also have the ALTER and DROP
privilege on the original table and CREATE and INSERT
privilege on the new table.
If MySQL encounters any errors in a multiple table rename, it will do a reverse rename for all renamed tables to get everything back to the original state.
DROP TABLE SyntaxDROP TABLE [IF EXISTS] tbl_name [, tbl_name,...] [RESTRICT | CASCADE]
DROP TABLE removes one or more tables. All table data and the table
definition are removed, so be careful with this command!
In MySQL Version 3.22 or later, you can use the keywords
IF EXISTS to prevent an error from occurring for tables that don't
exist.
RESTRICT and CASCADE are allowed to make porting easier.
For the moment they don't do anything.
OPTIMIZE TABLE SyntaxOPTIMIZE TABLE tbl_name[,tbl_name]...
OPTIMIZE TABLE should be used if you have deleted a large part of a
table or if you have made many changes to a table with variable-length rows
(tables that have VARCHAR, BLOB, or TEXT columns).
Deleted records are maintained in a linked list and subsequent INSERT
operations reuse old record positions. You can use OPTIMIZE TABLE to
reclaim the unused space and to defragment the data file.
For the moment OPTIMIZE TABLE only works on MyISAM and
BDB tables. For BDB tables, OPTIMIZE TABLE is
currently mapped to ANALYZE TABLE. See section 7.15 ANALYZE TABLE Syntax.
You can get optimize table to work on other table types by starting
mysqld with --skip-new or --safe-mode, but in this
case OPTIMIZE TABLE is just mapped to ALTER TABLE.
OPTIMIZE TABLE works the following way:
OPTIMIZE TABLE for MyISAM tables is equvialent of running
myisamchk --quick --check-changed-tables --sort-index --analyze
on the table.
Note that the table is locked during the time OPTIMIZE TABLE is
running!
CHECK TABLE SyntaxCHECK TABLE tbl_name[,tbl_name...] [option [option...]] option = QUICK | FAST | EXTEND | CHANGED
CHECK TABLE only works on MyISAM and BDB tables. On
MyISAM tables it's the same thing as running myisamchk -m
table_name on the table.
Checks the table(s) for errors. For MyISAM tables the key statistics
is updated. The command returns a table with the following columns:
| Column | Value |
| Table | Table name. |
| Op | Always ``check''. |
| Msg_type | One of status, error, info, or warning.
|
| Msg_text | The message. |
Note that you can get many rows of information for each checked
table. The last row will be of Msg_type status and should
normally be OK. If you don't get OK, or Not
checked you should normally run a repair of the table. See section 15.1 Using myisamchk for Table Maintenance and Crash Recovery. Not checked means that the table the given TYPE
told MySQL that there wasn't any need to check the table.
The different check types stand for the following:
| Type | Meaning |
QUICK | Don't scan the rows to check for wrong links. |
FAST | Only check tables which haven't been closed properly. |
CHANGED | Only check tables which have been changed since last check or haven't been closed properly. |
EXTENDED | Do a full key lookup for all keys for each row. This ensures that the table is 100 % consistent, but will take a long time! |
Note that for BDB tables the different check options doesn't affect the check in any way!
You can combine check options as in:
CHECK TABLE test_table FAST QUICK;
Which only would do a quick check on the table if it wasn't closed properly.
If a table is corrupted, then it's most likely that the problem is in the indexes and not in the data part. All of the above check types checks the indexes throughly and should thus find most errors.
If you just want to check a table that you assume is ok, you should use
no check options or the QUICK option. The later should be used
when you are in a hurry and can take the very small risk that
QUICK didn't find an error in the data file (In most cases
MySQL should find, under normal usage, any error in the data
file. If this happens then the table will be marked as 'corrupted',
in which case the table can't be used until it's repaired).
FAST and CHANGED are mostly intended to be used from a
script (for example to be executed from cron) if you want to check your
table from time to time. In most cases you FAST is to be prefered
over CHANGED. (The only case when it isn't is when you suspect a
bug you have found a bug in the MyISAM code.).
EXTENDED is only to be used after you have run a normal check but
still get strange errors from a table when MySQL tries to
update a row or find a row by key (this is VERY unlikely to happen if a
normal check has succeeded!).
BACKUP TABLE SyntaxBACKUP TABLE tbl_name[,tbl_name...] TO '/path/to/backup/directory'
Make a copy of all the table files to the backup directory that are the
minimum needed to restore it. Currenlty only works for MyISAM
tables. For MyISAM table, copies .frm (definition) and
.MYD (data) files. The index file can be rebuilt from those two.
During the backup, read lock will be held for each table, one at time,
as they are being backed up. If you want to backup several tables as
a snapshot, you must first issue LOCK TABLES obtaining a read
lock for each table in the group.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``backup'' |
| Msg_type | One of status, error, info or warning.
|
| Msg_text | The message. |
Note that BACKUP TABLE is only available in MySQL
version 3.23.25 and later.
RESTORE TABLE SyntaxRESTORE TABLE tbl_name[,tbl_name...] FROM '/path/to/backup/directory'
Restores the table(s) from the backup that was made with
BACKUP TABLE. Existing tables will not be overwritten - if you
try to restore over an existing table, you will get an error. Restore
will take longer than BACKUP due to the need to rebuilt the index. The
more keys you have, the longer it is going to take. Just as
BACKUP TABLE, currently only works of MyISAM tables.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``restore'' |
| Msg_type | One of status, error, info or warning.
|
| Msg_text | The message. |
ANALYZE TABLE SyntaxANALYZE TABLE tbl_name[,tbl_name...]
Analyze and store the key distribution for the table. During the
analyze the table is locked with a read lock. This works on
MyISAM and BDB tables.
This is equivalent to running myisamchk -a on the table.
MySQL uses the stored key distribution to decide in which order tables should be joined when one does a join on something else than a constant.
The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``analyze'' |
| Msg_type | One of status, error, info or warning.
|
| Msg_text | The message. |
You can check the stored key distribution with the SHOW INDEX command.
See section 7.28.1 SHOW Information About Databases, Tables, Columns, and Indexes.
If the table hasn't changed since the last ANALYZE TABLE command,
the table will not be analyzed again.
REPAIR TABLE SyntaxREPAIR TABLE tbl_name[,tbl_name...] [QUICK] [EXTENDED]
REPAIR TABLE only works on MyISAM tables and is the same
as running myisamchk -r table_name on the table.
Repair the corrupted table. The command returns a table with the following columns:
| Column | Value |
| Table | Table name |
| Op | Always ``repair'' |
| Msg_type | One of status, error, info or warning.
|
| Msg_text | The message. |
Note that you can get many rows of information for each repaired
table. The last one row will be of Msg_type status and should
normally be OK. If you don't get OK, you should try
repairing the table with myisamchk -o, as REPAIR TABLE
does not yet implement all the options of myisamchk. In the near
future, we will make it more flexible.
If QUICK is given then MySQL will try to do a
REPAIR of only the index tree.
If you use EXTENDED then MySQL will create the index row
by row instead of creating one index at a time with sorting; This may be
better than sorting on fixed-length keys if you have long char()
keys that compress very good.
DELETE Syntax
DELETE [LOW_PRIORITY] FROM tbl_name
[WHERE where_definition] [LIMIT rows]
DELETE deletes rows from tbl_name that satisfy the condition
given by where_definition, and returns the number of records deleted.
If you issue a DELETE with no WHERE clause, all rows are
deleted. If you do this in AUTOCOMMIT mode, this works as
TRUNCATE. See section 7.18 TRUNCATE Syntax. One problem with this is that
DELETE will return zero as the number of affected records, but
this will be fixed in 4.0.
If you really want to know how many records are deleted when you are deleting
all rows, and are willing to suffer a speed penalty, you can use a
DELETE statement of this form:
mysql> DELETE FROM tbl_name WHERE 1>0;
Note that this is MUCH slower than DELETE FROM tbl_name with no
WHERE clause, because it deletes rows one at a time.
If you specify the keyword LOW_PRIORITY, execution of the
DELETE is delayed until no other clients are reading from the table.
Deleted records are maintained in a linked list and subsequent INSERT
operations reuse old record positions. To reclaim unused space and reduce
file sizes, use the OPTIMIZE TABLE statement or the myisamchk
utility to reorganize tables. OPTIMIZE TABLE is easier, but
myisamchk is faster.
See section 7.11 OPTIMIZE TABLE Syntax and section 15.4.3 Table Optimization.
The MySQL-specific LIMIT rows option to DELETE tells
the server the maximum number of rows to be deleted before control is
returned to the client. This can be used to ensure that a specific
DELETE command doesn't take too much time. You can simply repeat
the DELETE command until the number of affected rows is less than
the LIMIT value.
TRUNCATE SyntaxTRUNCATE table_name
Is in 3.23 and the same thing as DELETE FROM table_name. See section 7.17 DELETE Syntax.
The differences are:
TRUNCATE will automaticly end the current
transaction as if COMMIT would have been called.
SELECT Syntax
SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
[HIGH_PRIORITY]
[DISTINCT | DISTINCTROW | ALL]
select_expression,...
[INTO {OUTFILE | DUMPFILE} 'file_name' export_options]
[FROM table_references
[WHERE where_definition]
[GROUP BY {unsigned_integer | col_name | formula}]
[HAVING where_definition]
[ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...]
[LIMIT [offset,] rows]
[PROCEDURE procedure_name] ]
SELECT is used to retrieve rows selected from one or more tables.
select_expression indicates the columns you want to retrieve.
SELECT may also be used to retrieve rows computed without reference to
any table. For example:
mysql> SELECT 1 + 1;
-> 2
All keywords used must be given in exactly the order shown above. For example,
a HAVING clause must come after any GROUP BY clause and before
any ORDER BY clause.
SELECT expression may be given an alias using AS. The alias
is used as the expression's column name and can be used with
ORDER BY or HAVING clauses. For example:
mysql> select concat(last_name,', ',first_name) AS full_name
from mytable ORDER BY full_name;
FROM table_references clause indicates the tables from which to
retrieve rows. If you name more than one table, you are performing a
join. For information on join syntax, see section 7.20 JOIN Syntax.
col_name, tbl_name.col_name, or
db_name.tbl_name.col_name. You need not specify a tbl_name or
db_name.tbl_name prefix for a column reference in a SELECT
statement unless the reference would be ambiguous. See section 7.1.5 Database, Table, Index, Column, and Alias Names,
for examples of ambiguity that require the more explicit column reference
forms.
tbl_name [AS] alias_name:
mysql> select t1.name, t2.salary from employee AS t1, info AS t2
where t1.name = t2.name;
mysql> select t1.name, t2.salary from employee t1, info t2
where t1.name = t2.name;
ORDER BY and
GROUP BY clauses using column names, column aliases, or column
positions. Column positions begin with 1:
mysql> select college, region, seed from tournament
ORDER BY region, seed;
mysql> select college, region AS r, seed AS s from tournament
ORDER BY r, s;
mysql> select college, region, seed from tournament
ORDER BY 2, 3;
To sort in reverse order, add the DESC (descending) keyword to the
name of the column in the ORDER BY clause that you are sorting by.
The default is ascending order; this may be specified explicitly using
the ASC keyword.
HAVING clause can refer to any column or alias named in the
select_expression. It is applied last, just before items are sent to
the client, with no optimization. Don't use HAVING for items that
should be in the WHERE clause. For example, do not write this:
mysql> select col_name from tbl_name HAVING col_name > 0;Write this instead:
mysql> select col_name from tbl_name WHERE col_name > 0;In MySQL Version 3.22.5 or later, you can also write queries like this:
mysql> select user,max(salary) from users
group by user HAVING max(salary)>10;
In older MySQL versions, you can write this instead:
mysql> select user,max(salary) AS sum from users
group by user HAVING sum>10;
SQL_SMALL_RESULT, SQL_BIG_RESULT, SQL_BUFFER_RESULT,
STRAIGHT_JOIN, and HIGH_PRIORITY are MySQL extensions
to ANSI SQL92.
HIGH_PRIORITY will give the SELECT higher priority than
a statement that updates a table. You should only use this for queries
that are very fast and must be done at once. A SELECT HIGH_PRIORITY
query will run if the table is locked for read even if there is an update
statement that is waiting for the table to be free.
SQL_BIG_RESULT can be used with GROUP BY or DISTINCT
to tell the optimizer that the result set will have many rows. In this case,
MySQL will directly use disk-based temporary tables if needed.
MySQL will also, in this case, prefer sorting to doing a
temporary table with a key on the GROUP BY elements.
SQL_BUFFER_RESULT will force the result to be put into a temporary
table. This will help MySQL free the table locks early and will help
in cases where it takes a long time to send the result set to the client.
SQL_SMALL_RESULT, a MySQL-specific option, can be used
with GROUP BY or DISTINCT to tell the optimizer that the
result set will be small. In this case, MySQL will use fast
temporary tables to store the resulting table instead of using sorting. In
MySQL Version 3.23 this shouldn't normally be needed.
STRAIGHT_JOIN forces the optimizer to join the tables in the order in
which they are listed in the FROM clause. You can use this to speed up
a query if the optimizer joins the tables in non-optimal order.
See section 7.29 EXPLAIN Syntax (Get Information About a SELECT).
LIMIT clause can be used to constrain the number of rows returned
by the SELECT statement. LIMIT takes one or two numeric
arguments.
If two arguments are given, the first specifies the offset of the first row to
return, the second specifies the maximum number of rows to return.
The offset of the initial row is 0 (not 1):
mysql> select * from table LIMIT 5,10; # Retrieve rows 6-15If one argument is given, it indicates the maximum number of rows to return:
mysql> select * from table LIMIT 5; # Retrieve first 5 rowsIn other words,
LIMIT n is equivalent to LIMIT 0,n.
SELECT ... INTO OUTFILE 'file_name' form of SELECT writes
the selected rows to a file. The file is created on the server host and
cannot already exist (among other things, this prevents database tables and
files such as `/etc/passwd' from being destroyed). You must have the
file privilege on the server host to use this form of SELECT.
SELECT ... INTO OUTFILE is the complement of LOAD DATA
INFILE; the syntax for the export_options part of the statement
consists of the same FIELDS and LINES clauses that are used
with the LOAD DATA INFILE statement.
See section 7.23 LOAD DATA INFILE Syntax.
In the resulting text file, only the following characters are escaped by
the ESCAPED BY character:
ESCAPED BY character
FIELDS TERMINATED BY
LINES TERMINATED BY
ASCII 0 is converted to ESCAPED BY followed by 0
(ASCII 48).
The reason for the above is that you MUST escape any FIELDS
TERMINATED BY, ESCAPED BY, or LINES TERMINATED BY
characters to reliably be able to read the file
back. ASCII 0 is escaped to make it easier to view with some
pagers.
As the resulting file doesn't have to conform to the SQL syntax, nothing
else need be escaped.
If you use INTO DUMPFILE instead of INTO OUTFILE, MySQL
will only write one row into the file, without any column or line
terminations and without any escaping. This is useful if you want to
store a blob in a file.
JOIN Syntax
MySQL supports the following JOIN syntaxes for use in
SELECT statements:
table_reference, table_reference
table_reference [CROSS] JOIN table_reference
table_reference INNER JOIN table_reference join_condition
table_reference STRAIGHT_JOIN table_reference
table_reference LEFT [OUTER] JOIN table_reference join_condition
table_reference LEFT [OUTER] JOIN table_reference
table_reference NATURAL [LEFT [OUTER]] JOIN table_reference
{ oj table_reference LEFT OUTER JOIN table_reference ON conditional_expr }
table_reference RIGHT [OUTER] JOIN table_reference join_condition
table_reference RIGHT [OUTER] JOIN table_reference
table_reference NATURAL [RIGHT [OUTER]] JOIN table_reference
Where table_reference is defined as:
table_name [[AS] alias] [USE INDEX (key_list)] [IGNORE INDEX (key_list)]
and join_condition is defined as:
ON conditional_expr | USING (column_list)
Note that in versions before Version 3.23.16, the INNER JOIN didn't take
a join condition!
The last LEFT OUTER JOIN syntax shown above exists only for
compatibility with ODBC:
tbl_name AS alias_name or
tbl_name alias_name:
mysql> select t1.name, t2.salary from employee AS t1, info AS t2
where t1.name = t2.name;
INNER JOIN and , (comma) are semantically equivalent.
Both do a full join between the tables used. Normally, you specify how
the tables should be linked in the WHERE condition.
ON conditional is any conditional of the form that may be used in
a WHERE clause.
ON or
USING part in a LEFT JOIN, a row with all columns set to
NULL is used for the right table. You can use this fact to find
records in a table that have no counterpart in another table:
mysql> select table1.* from table1
LEFT JOIN table2 ON table1.id=table2.id
where table2.id is NULL;
This example finds all rows in table1 with an id value that is
not present in table2 (that is, all rows in table1 with no
corresponding row in table2). This assumes that table2.id is
declared NOT NULL, of course. See section 12.5.5 How MySQL Optimizes LEFT JOIN and RIGHT JOIN.
USING (column_list) clause names a list of columns that must
exist in both tables. A USING clause such as:
A LEFT JOIN B USING (C1,C2,C3,...)is defined to be semantically identical to an
ON expression like
this:
A.C1=B.C1 AND A.C2=B.C2 AND A.C3=B.C3,...
NATURAL [LEFT] JOIN of two tables is defined to be
semantically equivalent to an INNER JOIN or a LEFT JOIN
with a USING clause that names all columns that exist in both
tables.
RIGHT JOIN works analogously as LEFT JOIN. To keep code
portable across databases, it's recommended to use LEFT JOIN
instead of RIGHT JOIN.
STRAIGHT_JOIN is identical to JOIN, except that the left table
is always read before the right table. This can be used for those (few)
cases where the join optimizer puts the tables in the wrong order.
EXPLAIN shows that MySQL is
using the wrong index. By specifying USE INDEX (key_list), you
can tell MySQL to use only one of the specified indexes to
find rows in the table. The alternative syntax IGNORE INDEX
(key_list) can be used to tell MySQL to not use some
particular index.
Some examples:
mysql> select * from table1,table2 where table1.id=table2.id;
mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id;
mysql> select * from table1 LEFT JOIN table2 USING (id);
mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id
LEFT JOIN table3 ON table2.id=table3.id;
mysql> select * from table1 USE INDEX (key1,key2) WHERE key1=1 and key2=2 AND
key3=3;
mysql> select * from table1 IGNORE INDEX (key3) WHERE key1=1 and key2=2 AND
key3=3;
See section 12.5.5 How MySQL Optimizes LEFT JOIN and RIGHT JOIN.
INSERT Syntax
INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name [(col_name,...)]
VALUES (expression,...),(...),...
or INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name [(col_name,...)]
SELECT ...
or INSERT [LOW_PRIORITY | DELAYED] [IGNORE]
[INTO] tbl_name
SET col_name=expression, col_name=expression, ...
INSERT inserts new rows into an existing table. The INSERT ...
VALUES form of the statement inserts rows based on explicitly specified
values. The INSERT ... SELECT form inserts rows selected from another
table or tables. The INSERT ... VALUES form with multiple value lists
is supported in MySQL Version 3.22.5 or later. The
col_name=expression syntax is supported in MySQL Version 3.22.10 or
later.
tbl_name is the table into which rows should be inserted. The column
name list or the SET clause indicates which columns the statement
specifies values for:
INSERT ... VALUES or INSERT
... SELECT, values for all columns must be provided in the
VALUES() list or by the SELECT. If you don't know the order of
the columns in the table, use DESCRIBE tbl_name to find out.
CREATE TABLE Syntax.
expression may refer to any column that was set earlier in a value
list. For example, you can say this:
mysql> INSERT INTO tbl_name (col1,col2) VALUES(15,col1*2);But not this:
mysql> INSERT INTO tbl_name (col1,col2) VALUES(col2*2,15);
LOW_PRIORITY, execution of the
INSERT is delayed until no other clients are reading from the table.
In this case the client has to wait until the insert statement is completed,
which may take a long time if the table is in heavy use. This is in
contrast to INSERT DELAYED, which lets the client continue at once.
Note that LOW_PRIORITY should normally not be used with MyISAM
tables as this disables concurrent inserts.See section 8.1 MyISAM Tables.
IGNORE in an INSERT with many value
rows, any rows that duplicate an existing PRIMARY or UNIQUE
key in the table are ignored and are not inserted. If you do not specify
IGNORE, the insert is aborted if there is any row that duplicates an
existing key value. You can determine with the C API function
mysql_info() how many rows were inserted into the table.
DONT_USE_DEFAULT_FIELDS
option, INSERT statements generate an error unless you explicitly
specify values for all columns that require a non-NULL value.
See section 4.7.3 Typical configure Options.
INSERT INTO ... SELECT statement:
ORDER BY clause.
INSERT statement cannot appear in the
FROM clause of the SELECT part of the query because it's
forbidden in ANSI SQL to SELECT from the same table into which you are
inserting. (The problem is that the SELECT possibly would
find records that were inserted earlier during the same run. When using
sub-select clauses, the situation could easily be very confusing!)
AUTO_INCREMENT columns work as usual.
If you use INSERT ... SELECT or an INSERT ... VALUES
statement with multiple value lists, you can use the C API function
mysql_info() to get information about the query. The format of the
information string is shown below:
Records: 100 Duplicates: 0 Warnings: 0
Duplicates indicates the number of rows that couldn't be inserted
because they would duplicate some existing unique index value.
Warnings indicates the number of attempts to insert column values that
were problematic in some way. Warnings can occur under any of the following
conditions:
NULL into a column that has been declared NOT NULL.
The column is set to its default value.
'10.34 a'. The trailing
garbage is stripped and the remaining numeric part is inserted. If the value
doesn't make sense as a number at all, the column is set to 0.
CHAR, VARCHAR, TEXT, or
BLOB column that exceeds the column's maximum length. The value is
truncated to the column's maximum length.
The DELAYED option
for the
INSERT statement is a MySQL-specific option that is very
useful if you have clients that can't wait for the INSERT to complete.
This is a common problem when you use MySQL for logging and you also
periodically run SELECT statements that take a long time to complete.
DELAYED was introduced in MySQL Version 3.22.15. It is a
MySQL extension to ANSI SQL92.
When you use INSERT DELAYED, the client will get an OK at once
and the row will be inserted when the table is not in use by any other thread.
Another major benefit of using INSERT DELAYED is that inserts
from many clients are bundled together and written in one block. This is much
faster than doing many separate inserts.
Note that currently the queued rows are only stored in memory until they are
inserted into the table. This means that if you kill mysqld
the hard way (kill -9) or if mysqld dies unexpectedly, any
queued rows that weren't written to disk are lost!
The following describes in detail what happens when you use the
DELAYED option to INSERT or REPLACE. In this
description, the ``thread'' is the thread that received an INSERT
DELAYED command and ``handler'' is the thread that handles all
INSERT DELAYED statements for a particular table.
DELAYED statement for a table, a handler
thread is created to process all DELAYED statements for the table, if
no such handler already exists.
DELAYED
lock already; if not, it tells the handler thread to do so. The
DELAYED lock can be obtained even if other threads have a READ
or WRITE lock on the table. However, the handler will wait for all
ALTER TABLE locks or FLUSH TABLES to ensure that the table
structure is up to date.
INSERT statement, but instead of writing
the row to the table, it puts a copy of the final row into a queue that
is managed by the handler thread. Any syntax errors are noticed by the
thread and reported to the client program.
AUTO_INCREMENT
value for the resulting row; it can't obtain them from the server, because
the INSERT returns before the insert operation has been completed. If
you use the C API, the mysql_info() function doesn't return anything
meaningful, for the same reason.
delayed_insert_limit rows are written, the handler checks
whether or not any SELECT statements are still pending. If so, it
allows these to execute before continuing.
INSERT DELAYED commands are received within
delayed_insert_timeout seconds, the handler terminates.
delayed_queue_size rows are pending already in a specific
handler queue, the thread waits until there is room in the queue. This is
useful to ensure that the mysqld server doesn't use all memory for the
delayed memory queue.
delayed_insert in the Command column. It will
be killed if you execute a FLUSH TABLES command or kill it with
KILL thread_id. However, it will first store all queued rows into the
table before exiting. During this time it will not accept any new
INSERT commands from another thread. If you execute an INSERT
DELAYED command after this, a new handler thread will be created.
INSERT DELAYED commands have higher
priority than normal INSERT commands if there is an INSERT
DELAYED handler already running! Other update commands will have to wait
until the INSERT DELAYED queue is empty, someone kills the handler
thread (with KILL thread_id), or someone executes FLUSH TABLES.
INSERT
DELAYED commands:
| Variable | Meaning |
Delayed_insert_threads | Number of handler threads |
Delayed_writes | Number of rows written with INSERT DELAYED
|
Not_flushed_delayed_rows | Number of rows waiting to be written |
SHOW STATUS statement or
by executing a mysqladmin extended-status command.
Note that INSERT DELAYED is slower than a normal INSERT if the
table is not in use. There is also the additional overhead for the
server to handle a separate thread for each table on which you use
INSERT DELAYED. This means that you should only use INSERT
DELAYED when you are really sure you need it!
REPLACE Syntax
REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name [(col_name,...)]
VALUES (expression,...)
or REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name [(col_name,...)]
SELECT ...
or REPLACE [LOW_PRIORITY | DELAYED]
[INTO] tbl_name
SET col_name=expression, col_name=expression,...
REPLACE works exactly like INSERT, except that if an old
record in the table has the same value as a new record on a unique index,
the old record is deleted before the new record is inserted.
See section 7.21 INSERT Syntax.
In other words, you can't access the values of the old row from a
REPLACE statement. In some old MySQL version it looked
like you could do this, but that was a bug that has been corrected.
LOAD DATA INFILE Syntax
LOAD DATA [LOW_PRIORITY] [LOCAL] INFILE 'file_name.txt' [REPLACE | IGNORE]
INTO TABLE tbl_name
[FIELDS
[TERMINATED BY '\t']
[[OPTIONALLY] ENCLOSED BY '']
[ESCAPED BY '\\' ]
]
[LINES TERMINATED BY '\n']
[IGNORE number LINES]
[(col_name,...)]
The LOAD DATA INFILE statement reads rows from a text file into a
table at a very high speed. If the LOCAL keyword is specified, the
file is read from the client host. If LOCAL is not specified, the
file must be located on the server. (LOCAL is available in
MySQL Version 3.22.6 or later.)
For security reasons, when reading text files located on the server, the
files must either reside in the database directory or be readable by all.
Also, to use LOAD DATA INFILE on server files, you must have the
file privilege on the server host.
See section 6.7 Privileges Provided by MySQL.
If you specify the keyword LOW_PRIORITY, execution of the
LOAD DATA statement is delayed until no other clients are reading
from the table.
Using LOCAL will be a bit slower than letting the server access the
files directly, because the contents of the file must travel from the client
host to the server host. On the other hand, you do not need the
file privilege to load local files.
If you are using MySQL before Version 3.23.24 you can't read from a
FIFO with LOAD DATA INFILE. If you need to read from a FIFO (for
example the output from gunzip), use LOAD DATA LOCAL INFILE
instead.
You can also load data files by using the mysqlimport utility; it
operates by sending a LOAD DATA INFILE command to the server. The
--local option causes mysqlimport to read data files from the
client host. You can specify the --compress option to get better
performance over slow networks if the client and server support the
compressed protocol.
When locating files on the server host, the server uses the following rules:
Note that these rules mean a file given as `./myfile.txt' is read from
the server's data directory, whereas a file given as `myfile.txt' is
read from the database directory of the current database. For example,
the following LOAD DATA statement reads the file `data.txt'
from the database directory for db1 because db1 is the current
database, even though the statement explicitly loads the file into a
table in the db2 database:
mysql> USE db1; mysql> LOAD DATA INFILE "data.txt" INTO TABLE db2.my_table;
The REPLACE and IGNORE keywords control handling of input
records that duplicate existing records on unique key values. If you specify
REPLACE, new rows replace existing rows that have the same unique key
value. If you specify IGNORE, input rows that duplicate an existing
row on a unique key value are skipped. If you don't specify either option, an
error occurs when a duplicate key value is found, and the rest of the text
file is ignored.
If you load data from a local file using the LOCAL keyword, the server
has no way to stop transmission of the file in the middle of the operation,
so the default bahavior is the same as if IGNORE is specified.
If you use LOAD DATA INFILE on an empty MyISAM table,
all non-unique indexes are created in a separate batch (like in REPAIR).
This normally makes LOAD DATA INFILE much faster when you have many
indexes.
LOAD DATA INFILE is the complement of SELECT ... INTO OUTFILE.
See section 7.19 SELECT Syntax.
To write data from a database to a file, use SELECT ... INTO OUTFILE.
To read the file back into the database, use LOAD DATA INFILE.
The syntax of the FIELDS and LINES clauses is the same for
both commands. Both clauses are optional, but FIELDS
must precede LINES if both are specified.
If you specify a FIELDS clause,
each of its subclauses (TERMINATED BY, [OPTIONALLY] ENCLOSED
BY, and ESCAPED BY) is also optional, except that you must
specify at least one of them.
If you don't specify a FIELDS clause, the defaults are the
same as if you had written this:
FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\'
If you don't specify a LINES clause, the default
is the same as if you had written this:
LINES TERMINATED BY '\n'
In other words, the defaults cause LOAD DATA INFILE to act as follows
when reading input:
Conversely, the defaults cause SELECT ... INTO OUTFILE to act as
follows when writing output:
Note that to write FIELDS ESCAPED BY '\\', you must specify two
backslashes for the value to be read as a single backslash.
The IGNORE number LINES option can be used to ignore a header of
column names at the start of the file:
mysql> LOAD DATA INFILE "/tmp/file_name" into table test IGNORE 1 LINES;
When you use SELECT ... INTO OUTFILE in tandem with LOAD
DATA INFILE to write data from a database into a file and then read
the file back into the database later, the field and line handling
options for both commands must match. Otherwise, LOAD DATA
INFILE will not interpret the contents of the file properly. Suppose
you use SELECT ... INTO OUTFILE to write a file with
fields delimited by commas:
mysql> SELECT * INTO OUTFILE 'data.txt'
FIELDS TERMINATED BY ','
FROM ...
To read the comma-delimited file back in, the correct statement would be:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2
FIELDS TERMINATED BY ',';
If instead you tried to read in the file with the statement shown below, it
wouldn't work because it instructs LOAD DATA INFILE to look for
tabs between fields:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2
FIELDS TERMINATED BY '\t';
The likely result is that each input line would be interpreted as a single field.
LOAD DATA INFILE can be used to read files obtained from
external sources, too. For example, a file in dBASE format will have
fields separated by commas and enclosed in double quotes. If lines in
the file are terminated by newlines, the command shown below
illustrates the field and line handling options you would use to load
the file:
mysql> LOAD DATA INFILE 'data.txt' INTO TABLE tbl_name
FIELDS TERMINATED BY ',' ENCLOSED BY '"'
LINES TERMINATED BY '\n';
Any of the field or line handling options may specify an empty string
(''). If not empty, the FIELDS [OPTIONALLY] ENCLOSED BY
and FIELDS ESCAPED BY values must be a single character. The
FIELDS TERMINATED BY and LINES TERMINATED BY values may
be more than one character. For example, to write lines that are
terminated by carriage return-linefeed pairs, or to read a file
containing such lines, specify a LINES TERMINATED BY '\r\n'
clause.
FIELDS [OPTIONALLY] ENCLOSED BY controls quoting of fields. For
output (SELECT ... INTO OUTFILE), if you omit the word
OPTIONALLY, all fields are enclosed by the ENCLOSED BY
character. An example of such output (using a comma as the field
delimiter) is shown below:
"1","a string","100.20" "2","a string containing a , comma","102.20" "3","a string containing a \" quote","102.20" "4","a string containing a \", quote and comma","102.20"
If you specify OPTIONALLY, the ENCLOSED BY character is
used only to enclose CHAR and VARCHAR fields:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a \" quote",102.20 4,"a string containing a \", quote and comma",102.20
Note that occurrences of the ENCLOSED BY character within a
field value are escaped by prefixing them with the ESCAPED BY
character. Also note that if you specify an empty ESCAPED BY
value, it is possible to generate output that cannot be read properly by
LOAD DATA INFILE. For example, the output just shown above would
appear as shown below if the escape character is empty. Observe that the
second field in the fourth line contains a comma following the quote, which
(erroneously) appears to terminate the field:
1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a " quote",102.20 4,"a string containing a ", quote and comma",102.20
For input, the ENCLOSED BY character, if present, is stripped from the
ends of field values. (This is true whether or not OPTIONALLY is
specified; OPTIONALLY has no effect on input interpretation.)
Occurrences of the ENCLOSED BY character preceded by the
ESCAPED BY character are interpreted as part of the current field
value. In addition, duplicated ENCLOSED BY characters occurring
within fields are interpreted as single ENCLOSED BY characters if the
field itself starts with that character. For example, if ENCLOSED BY
'"' is specified, quotes are handled as shown below:
"The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss The ""BIG"" boss -> The ""BIG"" boss
FIELDS ESCAPED BY controls how to write or read special characters.
If the FIELDS ESCAPED BY character is not empty, it is used to prefix
the following characters on output:
FIELDS ESCAPED BY character
FIELDS [OPTIONALLY] ENCLOSED BY character
FIELDS TERMINATED BY and
LINES TERMINATED BY values
0 (what is actually written following the escape character is
ASCII '0', not a zero-valued byte)
If the FIELDS ESCAPED BY character is empty, no characters are escaped.
It is probably not a good idea to specify an empty escape character,
particularly if field values in your data contain any of the characters in
the list just given.
For input, if the FIELDS ESCAPED BY character is not empty, occurrences
of that character are stripped and the following character is taken literally
as part of a field value. The exceptions are an escaped `0' or
`N' (for example, \0 or \N if the escape character is
`\'). These sequences are interpreted as ASCII 0 (a zero-valued
byte) and NULL. See below for the rules on NULL handling.
For more information about `\'-escape syntax, see section 7.1 Literals: How to Write Strings and Numbers.
In certain cases, field and line handling options interact:
LINES TERMINATED BY is an empty string and FIELDS
TERMINATED BY is non-empty, lines are also terminated with
FIELDS TERMINATED BY.
FIELDS TERMINATED BY and FIELDS ENCLOSED BY values are
both empty (''), a fixed-row (non-delimited) format is used. With
fixed-row format, no delimiters are used between fields. Instead, column
values are written and read using the ``display'' widths of the columns. For
example, if a column is declared as INT(7), values for the column are
written using 7-character fields. On input, values for the column are
obtained by reading 7 characters. Fixed-row format also affects handling of
NULL values; see below. Note that fixed-size format will not work
if you are using a multi-byte character set.
Handling of NULL values varies, depending on the FIELDS and
LINES options you use:
FIELDS and LINES values,
NULL is written as \N for output and \N is read
as NULL for input (assuming the ESCAPED BY character
is `\').
FIELDS ENCLOSED BY is not empty, a field containing the literal
word NULL as its value is read as a NULL value (this differs
from the word NULL enclosed within FIELDS ENCLOSED BY
characters, which is read as the string 'NULL').
FIELDS ESCAPED BY is empty, NULL is written as the word
NULL.
FIELDS TERMINATED BY and
FIELDS ENCLOSED BY are both empty), NULL is written as an empty
string. Note that this causes both NULL values and empty strings in
the table to be indistinguishable when written to the file because they are
both written as empty strings. If you need to be able to tell the two apart
when reading the file back in, you should not use fixed-row format.
Some cases are not supported by LOAD DATA INFILE:
FIELDS TERMINATED BY and FIELDS ENCLOSED
BY both empty) and BLOB or TEXT columns.
LOAD DATA INFILE won't be able to interpret the input properly.
For example, the following FIELDS clause would cause problems:
FIELDS TERMINATED BY '"' ENCLOSED BY '"'
FIELDS ESCAPED BY is empty, a field value that contains an occurrence
of FIELDS ENCLOSED BY or LINES TERMINATED BY
followed by the FIELDS TERMINATED BY value will cause LOAD
DATA INFILE to stop reading a field or line too early.
This happens because LOAD DATA INFILE cannot properly determine
where the field or line value ends.
The following example loads all columns of the persondata table:
mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata;
No field list is specified, so LOAD DATA INFILE expects input rows
to contain a field for each table column. The default FIELDS and
LINES values are used.
If you wish to load only some of a table's columns, specify a field list:
mysql> LOAD DATA INFILE 'persondata.txt'
INTO TABLE persondata (col1,col2,...);
You must also specify a field list if the order of the fields in the input file differs from the order of the columns in the table. Otherwise, MySQL cannot tell how to match up input fields with table columns.
If a row has too few fields, the columns for which no input field is present
are set to default values. Default value assignment is described in
section 7.7 CREATE TABLE Syntax.
An empty field value is interpreted differently than if the field value is missing:
0.
TIMESTAMP columns are only set to the current date and time if there
is a NULL value for the column, or (for the first TIMESTAMP
column only) if the TIMESTAMP column is left out from the field list
when a field list is specified.
If an input row has too many fields, the extra fields are ignored and the number of warnings is incremented.
LOAD DATA INFILE regards all input as strings, so you can't use
numeric values for ENUM or SET columns the way you can with
INSERT statements. All ENUM and SET values must be
specified as strings!
If you are using the C API, you can get information about the query by
calling the API function mysql_info() when the LOAD DATA INFILE
query finishes. The format of the information string is shown below:
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
Warnings occur under the same circumstances as when values are inserted
via the INSERT statement (see section 7.21 INSERT Syntax), except
that LOAD DATA INFILE also generates warnings when there are too few
or too many fields in the input row. The warnings are not stored anywhere;
the number of warnings can only be used as an indication if everything went
well. If you get warnings and want to know exactly why you got them, one way
to do this is to use SELECT ... INTO OUTFILE into another file and
compare this to your original input file.
If you need LOAD DATA to read from a pipe, you can use the
following trick:
mkfifo /mysql/db/x/x chmod 666 /mysql/db/x/x cat < /dev/tcp/10.1.1.12/4711 > /nt/mysql/db/x/x mysql -e "LOAD DATA INFILE 'x' INTO TABLE x" x
If you are using a version of MySQL older than 3.23.25
you can only do the above with LOAD DATA LOCAL INFILE.
For more information about the efficiency of INSERT versus
LOAD DATA INFILE and speeding up LOAD DATA INFILE,
See section 12.5.7 Speed of INSERT Queries.
UPDATE Syntax
UPDATE [LOW_PRIORITY] [IGNORE] tbl_name SET col_name1=expr1,col_name2=expr2,...
[WHERE where_definition] [LIMIT #]
UPDATE updates columns in existing table rows with new values. The
SET clause indicates which columns to modify and the values they
should be given. The WHERE clause, if given, specifies which rows
should be updated. Otherwise all rows are updated.
If you specify the keyword LOW_PRIORITY, execution of the
UPDATE is delayed until no other clients are reading from the table.
If you specify the keyword IGNORE, the update statement will not
abort even if we get duplicate key errors during the update. Rows that
would cause conflicts will not be updated.
If you access a column from tbl_name in an expression,
UPDATE uses the current value of the column. For example, the
following statement sets the age column to one more than its
current value:
mysql> UPDATE persondata SET age=age+1;
UPDATE assignments are evaluated from left to right. For example, the
following statement doubles the age column, then increments it:
mysql> UPDATE persondata SET age=age*2, age=age+1;
If you set a column to the value it currently has, MySQL notices this and doesn't update it.
UPDATE returns the number of rows that were actually changed.
In MySQL Version 3.22 or later, the C API function mysql_info()
returns the number of rows that were matched and updated and the number of
warnings that occurred during the UPDATE.
In MySQL Version 3.23, you can use LIMIT # to ensure that
only a given number of rows are changed.
USE SyntaxUSE db_name
The USE db_name statement tells MySQL to use the db_name
database as the default database for subsequent queries. The database remains
current until the end of the session or until another USE statement
is issued:
mysql> USE db1; mysql> SELECT count(*) FROM mytable; # selects from db1.mytable mysql> USE db2; mysql> SELECT count(*) FROM mytable; # selects from db2.mytable
Making a particular database current by means of the USE statement
does not preclude you from accessing tables in other databases. The example
below accesses the author table from the db1 database and the
editor table from the db2 database:
mysql> USE db1;
mysql> SELECT author_name,editor_name FROM author,db2.editor
WHERE author.editor_id = db2.editor.editor_id;
The USE statement is provided for Sybase compatibility.
FLUSH Syntax (Clearing Caches)FLUSH flush_option [,flush_option]
You should use the FLUSH command if you want to clear some of the
internal caches MySQL uses. To execute FLUSH, you must have
the reload privilege.
flush_option can be any of the following:
HOSTS | Empties the host cache tables. You should flush the
host tables if some of your hosts change IP number or if you get the
error message Host ... is blocked. When more than
max_connect_errors errors occur in a row for a given host while
connection to the MySQL server, MySQL assumes
something is wrong and blocks the host from further connection requests.
Flushing the host tables allows the host to attempt to connect
again. See section 20.4.3 Host '...' is blocked Error.) You can start mysqld with
-O max_connection_errors=999999999 to avoid this error message.
|
LOGS | Closes and reopens all log files. If you have specified the update log file or a binary log file without an extension, the extension number of the log file will be incremented by one relative to the previous file. If you have used an extension in the file name, MySQL will close and reopen the update log file. See section 21.3 The Update Log. |
PRIVILEGES | Reloads the privileges from the grant tables in
the mysql database.
|
TABLES | Closes all open tables and force all tables in use to be closed. |
[TABLE | TABLES] table_name [,table_name...] | Flushes only the given tables. |
TABLES WITH READ LOCK | Closes all open tables and locks all tables for all databases with a read until one executes UNLOCK TABLES. This is very convinient way to get backups if you have a file system, like Veritas,that can take snapshots in time.
|
STATUS | Resets most status variables to zero. |
You can also access each of the commands shown above with the mysqladmin
utility, using the flush-hosts, flush-logs, reload,
or flush-tables commands.
KILL SyntaxKILL thread_id
Each connection to mysqld runs in a separate thread. You can see
which threads are running with the SHOW PROCESSLIST command and kill
a thread with the KILL thread_id command.
If you have the process privilege, you can see and kill all threads. Otherwise, you can see and kill only your own threads.
You can also use the mysqladmin processlist and mysqladmin kill
commands to examine and kill threads.
SHOW Syntax (Get Information About Tables, Columns,...)SHOW DATABASES [LIKE wild] or SHOW TABLES [FROM db_name] [LIKE wild] or SHOW COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] or SHOW INDEX FROM tbl_name [FROM db_name] or SHOW TABLE STATUS [FROM db_name] [LIKE wild] or SHOW STATUS [LIKE wild] or SHOW VARIABLES [LIKE wild] or SHOW LOGS or SHOW [FULL] PROCESSLIST or SHOW GRANTS FOR user or SHOW CREATE TABLE table_name
SHOW provides information about databases, tables, columns, or
status information about the server. If the LIKE wild part is
used, the wild string can be a string that uses the SQL `%'
and `_' wild-card characters.
You can use db_name.tbl_name as an alternative to the tbl_name
FROM db_name syntax. These two statements are equivalent:
mysql> SHOW INDEX FROM mytable FROM mydb; mysql> SHOW INDEX FROM mydb.mytable;
SHOW DATABASES lists the databases on the MySQL server
host. You can also get this list using the mysqlshow command.
SHOW TABLES lists the tables in a given database. You can also
get this list using the mysqlshow db_name command.
NOTE: If a user doesn't have any privileges for a table, the table
will not show up in the output from SHOW TABLES or mysqlshow
db_name.
SHOW COLUMNS lists the columns in a given table. If the column
types are different than you expect them to be based on a CREATE
TABLE statement, note that MySQL sometimes changes column
types. See section 7.7.1 Silent Column Specification Changes.
The DESCRIBE statement provides information similar to
SHOW COLUMNS.
See section 7.30 DESCRIBE Syntax (Get Information About Columns).
SHOW FIELDS is a synonym for SHOW COLUMNS, and
SHOW KEYS is a synonym for SHOW INDEX. You can also
list a table's columns or indexes with mysqlshow db_name tbl_name
or mysqlshow -k db_name tbl_name.
SHOW INDEX returns the index information in a format that closely
resembles the SQLStatistics call in ODBC. The following columns
are returned:
| Column | Meaning |
Table | Name of the table. |
Non_unique | 0 if the index can't contain duplicates. |
Key_name | Name of the index. |
Seq_in_index | Column sequence number in index, starting with 1. |
Column_name | Column name. |
Collation | How the column is sorted in the index. In
MySQL, this can have values A (Ascending) or NULL
(Not sorted).
|
Cardinality | Number of unique values in the index.
This is updated by running isamchk -a.
|
Sub_part | Number of indexed characters if the column is
only partly indexed. NULL if the entire key is indexed.
|
Comment | Various remarks. For now, it tells whether index is FULLTEXT or not. |
SHOW TABLE STATUS (new in Version 3.23) works likes SHOW
STATUS, but provides a lot of information about each table. You can
also get this list using the mysqlshow --status db_name command.
The following columns are returned:
| Column | Meaning |
Name | Name of the table. |
Type | Type of table (BDB, ISAM, MERGE, MyISAM, or HEAP). |
Row_format | The row storage format (Fixed, Dynamic, or Compressed). |
Rows | Number of rows. |
Avg_row_length | Average row length. |
Data_length | Length of the data file. |
Max_data_length | Max length of the data file. |
Index_length | Length of the index file. |
Data_free | Number of allocated but not used bytes. |
Auto_increment | Next autoincrement value. |
Create_time | When the table was created. |
Update_time | When the data file was last updated. |
Check_time | When the table was last checked. |
Create_options | Extra options used with CREATE TABLE.
|
Comment | The comment used when creating the table (or some information why MySQL couldn't access the table information). |
SHOW STATUS provides server status information
(like mysqladmin extended-status). The output resembles that shown
below, though the format and numbers probably differ:
+--------------------------+------------+ | Variable_name | Value | +--------------------------+------------+ | Aborted_clients | 0 | | Aborted_connects | 0 | | Bytes_received | 142160923 | | Bytes_sent | 1161910370 | | Connections | 30022 | | Created_tmp_disk_tables | 0 | | Created_tmp_tables | 8988 | | Delayed_insert_threads | 0 | | Delayed_writes | 0 | | Delayed_errors | 0 | | Flush_commands | 1 | | Handler_delete | 462604 | | Handler_read_first | 95882 | | Handler_read_key | 27681068 | | Handler_read_next | 265008218 | | Handler_read_prev | 3022500 | | Handler_read_rnd | 36900998 | | Handler_read_rnd_next | 252097176 | | Handler_update | 16945404 | | Handler_write | 66826676 | | Key_blocks_used | 14955 | | Key_read_requests | 90131960 | | Key_reads | 163268 | | Key_write_requests | 7573912 | | Key_writes | 3780151 | | Max_used_connections | 0 | | Not_flushed_key_blocks | 0 | | Not_flushed_delayed_rows | 0 | | Open_tables | 0 | | Open_files | 0 | | Open_streams | 0 | | Opened_tables | 44598 | | Questions | 1866024 | | Select_full_join | 0 | | Select_full_range_join | 0 | | Select_range | 68187 | | Select_range_check | 0 | | Select_scan | 31440 | | Slave_running | OFF | | Slow_launch_threads | 0 | | Slow_queries | 0 | | Sort_range | 0 | | Sort_rows | 36650500 | | Sort_scan | 5298 | | Threads_cached | 0 | | Threads_connected | 1 | | Threads_running | 1 | | Uptime | 39613 | +--------------------------+------------+
The status variables listed above have the following meaning:
| Variable | Meaning |
Aborted_clients | Number of connections aborted because the client died without closing the connection properly. |
Aborted_connects | Number of tries to connect to the MySQL server that failed. |
Bytes_received | Number of bytes received from all clients. |
Bytes_sent | Number of bytes sent to all clients. |
Connections | Number of connection attempts to the MySQL server. |
Created_tmp_disk_tables | Number of implicit temporary tables on disk created while executing statements. |
Created_tmp_tables | Number of implicit temporary tables in memory created while executing statements. |
Created_tmp_files | How many temporary files mysqld have created.
|
Delayed_insert_threads | Number of delayed insert handler threads in use. |
Delayed_writes | Number of rows written with INSERT DELAYED.
|
Delayed_errors | Number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).
|
Flush_commands | Number of executed FLUSH commands.
|
Handler_delete | Number of times a row was deleted from a table. |
Handler_read_first | Number of times the first entry was read from an index.
If this is high, it suggests that the server is doing a lot of full index scans, for example,
SELECT col1 FROM foo, assuming that col1 is indexed.
|
Handler_read_key | Number of requests to read a row based on a key. If this is high, it is a good indication that your queries and tables are properly indexed. |
Handler_read_next | Number of requests to read next row in key order. This will be incremented if you are querying an index column with a range contraint. This also will be incremented if you are doing an index scan. |
Handler_read_rnd | Number of requests to read a row based on a fixed position. This will be high if you are doing a lot of queries that require sorting of the result. |
Handler_read_rnd_next | Number of requests to read the next row in the datafile. This will be high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have. |
Handler_update | Number of requests to update a row in a table. |
Handler_write | Number of requests to insert a row in a table. |
Key_blocks_used | The number of used blocks in the key cache. |
Key_read_requests | The number of requests to read a key block from the cache. |
Key_reads | The number of physical reads of a key block from disk. |
Key_write_requests | The number of requests to write a key block to the cache. |
Key_writes | The number of physical writes of a key block to disk. |
Max_used_connections | The maximum number of connections in use simultaneously. |
Not_flushed_key_blocks | Keys blocks in the key cache that has changed but hasn't yet been flushed to disk. |
Not_flushed_delayed_rows | Number of rows waiting to be written in INSERT DELAY queues.
|
Open_tables | Number of tables that are open. |
Open_files | Number of files that are open. |
Open_streams | Number of streams that are open (used mainly for logging). |
Opened_tables | Number of tables that have been opened. |
Select_full_join | Number of joins without keys (Should be 0). |
Select_full_range_join | Number of joins where we used a range search on reference table. |
Select_range | Number of joins where we used ranges on the first table. (It's normally not critical even if this is big.) |
Select_scan | Number of joins where we scanned the first table. |
Select_range_check | Number of joins without keys where we check for key usage after each row (Should be 0). |
Questions | Number of queries sent to the server. |
Slave_open_temp_tables | Number of temporary tables currently open by the slave thread |
Slow_launch_threads | Number of threads that have taken more than slow_launch_time to connect.
|
Slow_queries | Number of queries that have taken more than long_query_time. See section 21.5 The Slow Query Log.
|
Sort_merge_passes | Number of merges the sort has to do. If this value is large you should consider increasing sort_buffer.
|
Sort_range | Number of sorts that where done with ranges. |
Sort_rows | Number of sorted rows. |
Sort_scan | Number of sorts that where done by scanning the table. |
Threads_cached | Number of threads in the thread cache. |
Threads_connected | Number of currently open connections. |
Threads_running | Number of threads that are not sleeping. |
Uptime | How many seconds the server has been up. |
Some comments about the above:
Opened_tables is big, then your table_cache
variable is probably too small.
key_reads is big, then your key_cache is probably too
small. The cache hit rate can be calculated with
key_reads/key_read_requests.
Handler_read_rnd is big, then you probably have a lot of
queries that require MySQL to scan whole tables or you have
joins that don't use keys properly.
Created_tmp_tables or Sort_merge_passes are high then
your mysqld sort_buffer variables is probably too small.
Created_tmp_files doesn't count the files needed to handle temporary
tables.
SHOW VARIABLES shows the values of some MySQL system
variables. You can also get this information using the mysqladmin
variables command. If the default values are unsuitable, you can set most
of these variables using command-line options when mysqld starts up.
See section 4.16.4 Command-line Options.
The output resembles that shown below, though the format and numbers may differ somewhat:
+-------------------------+---------------------------------+ | Variable_name | Value | +-------------------------+---------------------------------+ | ansi_mode | OFF | | back_log | 50 | | basedir | /usr/local/mysql/ | | bdb_cache_size | 1048540 | | bdb_home | /usr/local/mysql/data/ | | bdb_logdir | | | bdb_tmpdir | /tmp/ | | binlog_cache_size | 32768 | | character_set | latin1 | | character_sets | latin1 | | connect_timeout | 5 | | concurrent_insert | ON | | datadir | /usr/local/mysql/data/ | | delay_key_write | ON | | delayed_insert_limit | 100 | | delayed_insert_timeout | 300 | | delayed_queue_size | 1000 | | join_buffer_size | 131072 | | flush | OFF | | flush_time | 0 | | init_file | | | interactive_timeout | 28800 | | key_buffer_size | 16776192 | | language | /usr/local/mysql/share/english/ | | log | OFF | | log_update | OFF | | log_bin | OFF | | log_slave_updates | OFF | | long_query_time | 10 | | low_priority_updates | OFF | | lower_case_table_names | 0 | | max_allowed_packet | 1047552 | | max_connections | 100 | | max_connect_errors | 10 | | max_delayed_threads | 20 | | max_heap_table_size | 16777216 | | max_join_size | 4294967295 | | max_sort_length | 1024 | | max_tmp_tables | 32 | | max_write_lock_count | 4294967295 | | myisam_sort_buffer_size | 8388608 | | net_buffer_length | 16384 | | net_retry_count | 10 | | pid_file | /usr/local/mysql/data/tik.pid | | port | 3306 | | protocol_version | 10 | | record_buffer | 131072 | | skip_locking | ON | | skip_networking | OFF | | skip_show_database | OFF | | slow_launch_time | 2 | | socket | /tmp/mysql.sock | | sort_buffer | 2097116 | | table_cache | 64 | | table_type | MYISAM | | thread_stack | 131072 | | thread_cache_size | 3 | | tmp_table_size | 1048576 | | tmpdir | /tmp/ | | version | 3.23.21-beta-debug | | wait_timeout | 28800 | +-------------------------+---------------------------------+
Each option is described below. Values for buffer sizes, lengths, and stack
sizes are given in bytes. You can specify values with a suffix of `K'
or `M' to indicate kilobytes or megabytes. For example, 16M
indicates 16 megabytes. The case of suffix letters does not matter;
16M and 16m are equivalent:
ansi_mode.ON if mysqld was started with --ansi.
See section 5.2 Running MySQL in ANSI Mode.
back_logback_log value indicates how many requests can be
stacked during this short time before MySQL momentarily stops
answering new requests. You need to increase this only if you expect a large
number of connections in a short period of time.
In other words, this value is the size of the listen queue for incoming
TCP/IP connections. Your operating system has its own limit on the size
of this queue. The manual page for the Unix listen(2) system
call should have more details. Check your OS documentation for the
maximum value for this variable. Attempting to set back_log
higher than your operating system limit will be ineffective.
basedir--basedir option.
bdb_cache_sizeBDB
tables. If you don't use BDB tables, you should set this to 0 or
start mysqld with --skip-bdb to not waste memory for this
cache.
bdb_home--bdb-home option.
bdb_max_lockbdb:
Lock table is out of available locks or Got error 12 from ...
when you have do long transactions or when mysqld has to examine
a lot of rows to calculate the query.
bdb_logdir--bdb-logdir option.
bdb_shared_dataON if you are using --bdb-shared-data.
bdb_tmpdir--bdb-tmpdir option.
binlog_cache_size. The size of the cache to hold the SQLBEGIN/COMMIT/ROLLBACK Syntax.
character_setcharacter_setsconcurrent_insertsON (the default), MySQL will allow you to use INSERT
on MyISAM tables at the same time as you run SELECT queries
on them. You can turn this option off by starting mysqld with --safe
or --skip-new.
connect_timeoutmysqld server is waiting for a connect
packet before responding with Bad handshake.
datadir--datadir option.
delay_key_writedelay_key_write option CREATE TABLE. This means that the
key buffer for tables with this option will not get flushed on every
index update, but only when a table is closed. This will speed up
writes on keys a lot, but you should add automatic checking of all tables
with myisamchk --fast --force if you use this. Note that if you
start mysqld with the --delay-key-write-for-all-tables
option this means that all tables will be treated as if they were
created with the delay_key_write option. You can clear this flag
by starting mysqld with --skip-new or --safe-mode.
delayed_insert_limitdelayed_insert_limit rows, the INSERT
DELAYED handler will check if there are any SELECT statements
pending. If so, it allows these to execute before continuing.
delayed_insert_timeoutINSERT DELAYED thread should wait for INSERT
statements before terminating.
delayed_queue_sizeINSERT
DELAYED. If the queue becomes full, any client that does INSERT
DELAYED will wait until there is room in the queue again.
flushON if you have started MySQL with the --flush
option.
flush_timeflush_time seconds all
tables will be closed (to free up resources and sync things to disk). We
only recommend this option on Win95, Win98, or on systems where you have
very little resources.
init_file--init-file option when
you start the server. This is a file of SQL statements you want the
server to execute when it starts.
interactive_timeoutCLIENT_INTERACTIVE option to
mysql_real_connect(). See also wait_timeout.
join_buffer_sizekey_buffer_sizekey_buffer_size is the size of the buffer used for index blocks.
Increase this to get better index handling (for all reads and multiple
writes) to as much as you can afford; 64M on a 256M machine that mainly
runs MySQL is quite common. If you, however, make this too big
(more than 50% of your total memory?) your system may start to page and
become REALLY slow. Remember that because MySQL does not cache
data read, that you will have to leave some room for the OS filesystem
cache.
You can check the performance of the key buffer by doing show
status and examine the variables Key_read_requests,
Key_reads, Key_write_requests, and Key_writes. The
Key_reads/Key_read_request ratio should normally be < 0.01.
The Key_write/Key_write_requests is usually near 1 if you are
using mostly updates/deletes but may be much smaller if you tend to
do updates that affect many at the same time or if you are
using delay_key_write. See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
To get even more speed when writing many rows at the same time, use
LOCK TABLES. See section 7.32 LOCK TABLES/UNLOCK TABLES Syntax.
languagelarge_file_supportmysqld was compiled with options for big file support.
locked_in_memorymysqld was locked in memory with --memlock
loglog_updatelog_binlog_slave_updateslong_query_timeSlow_queries counter
will be incremented. If you are using --log-slow-queries, the query
will be logged to the slow query logfile. See section 21.5 The Slow Query Log.
lower_case_table_namesmax_allowed_packetnet_buffer_length bytes, but can grow up to max_allowed_packet
bytes when needed. This value by default is small, to catch big (possibly
wrong) packets. You must increase this value if you are using big
BLOB columns. It should be as big as the biggest BLOB you want
to use. The current protocol limits max_allowed_packet to 16M.
max_binlog_cache_size. If a multi-statement transactionmax_connectionsmysqld requires. See below for
comments on file descriptor limits. See section 20.4.4 Too many connections Error.
max_connect_errorsFLUSH HOSTS.
max_delayed_threadsINSERT DELAYED
statements. If you try to insert data into a new table after all INSERT
DELAYED threads are in use, the row will be inserted as if the
DELAYED attribute wasn't specified.
max_heap_table_sizemax_join_sizemax_join_size
records return an error. Set this value if your users tend to perform joins
that lack a WHERE clause, that take a long time, and that return
millions of rows.
max_sort_lengthBLOB or TEXT
values (only the first max_sort_length bytes of each value
are used; the rest are ignored).
max_tmp_tablesmax_write_lock_countmyisam_recover_options--myisam-recover option.
myisam_sort_buffer_sizeREPAIR or when creating indexes with CREATE INDEX or
ALTER TABLE.
net_buffer_lengthmax_allowed_packet bytes.)
net_read_timeoutwrite_timeout.
net_retry_countFreeBSD as
internal interrupts are sent to all threads.
net_write_timeoutpid_file--pid-file option.
port--port option.
protocol_versionMySQL server.
record_bufferquery_buffer_sizeserver_id--server-id option.
skip_lockingmysqld uses external locking.
skip_networkingskip_show_databasesSHOW DATABASES if they don't
have the PROCESS_PRIV privilege. This can improve security if
you're concerned about people being able to see what databases and
tables other users have.
slow_launch_timeSlow_launch_threads counter will be incremented.
socketsort_bufferORDER BY or GROUP BY
operations.
See section 20.7 Where MySQL Stores Temporary Files.
table_cachemysqld requires.
MySQL needs two file descriptors for each unique open table.
See below for comments on file descriptor limits. You can check if you
need to increase the table cache by checking the Opened_tables
variable. See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...). If this variable is big and you don't do
FLUSH TABLES a lot (which just forces all tables to be closed and
reopenend), then you should increase the value of this variable.
Make sure that your operating system can handle the number of open file
descriptors implied by the table_cache setting. If table_cache
is set too high, MySQL may run out of file descriptors and refuse
connections, fail to perform queries, and be very unreliable.
For information about how the table cache works, see section 12.2.4 How MySQL Opens and Closes Tables.
table_typethread_cache_sizethread_cache_size threads from before. All new
threads are first taken from the cache, and only when the cache is empty
is a new thread created. This variable can be increased to improve
performance if you have a lot of new connections. (Normally this doesn't
give a notable performance improvement if you have a good
thread implementation.)
thread_concurrencymysqld will call thr_setconcurrency() with
this value. thr_setconcurrency() permits the application to give
the threads system a hint for the desired number of threads that should
be run at the same time.
thread_stackcrash-me test are dependent on this value. The default is
large enough for normal operation. See section 12.7 Using Your Own Benchmarks.
timezonetmp_table_sizeMyISAM table.
Increase the value of tmp_table_size if you do many advanced
GROUP BY queries and you have lots of memory.
tmpdirversionwait_timeoutinteractive_timeout.
The manual section that describes tuning MySQL contains some information of how to tune the above variables. See section 12.2.3 Tuning Server Parameters.
SHOW LOGS shows you status information about existing log
files. It currently only displays information about Berkeley DB log
files.
File shows the full path to the log file
Type shows the type of the log file (BDB for Berkeley
DB log files)
Status shows the status of the log file (FREE if the
file can be removed, or IN USE if the file is needed by the transaction
subsystem)
SHOW PROCESSLIST shows you which threads are running. You can
also get this information using the mysqladmin processlist
command. If you have the process privilege, you can see all
threads. Otherwise, you can see only your own threads. See section 7.27 KILL Syntax. If you don't use the FULL option, then only
the first 100 characters of each query will be shown.
This command is very useful if you get the 'too many connections' error
message and want to find out what's going on. MySQL reserves
one extra connection for a client with the Process_priv privilege
to ensure that you should always be able to login and check the system
(assuming you are not giving this privilege to all your users).
SHOW GRANTS FOR user lists the grant commands that must be issued to
duplicate the grants for a user.
mysql> SHOW GRANTS FOR root@localhost; +---------------------------------------------------------------------+ | Grants for root@localhost | +---------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION | +---------------------------------------------------------------------+
Shows a CREATE TABLE statement that will create the given table:
mysql> show create table t\G
*************************** 1. row ***************************
Table: t
Create Table: CREATE TABLE t (
id int(11) default NULL auto_increment,
s char(60) default NULL,
PRIMARY KEY (id)
) TYPE=MyISAM
SHOW CREATE TABLE will quote table and column names according to
SQL_QUOTE_SHOW_CREATE option.
section 7.33 SET Syntax.
EXPLAIN Syntax (Get Information About a SELECT)
EXPLAIN tbl_name
or EXPLAIN SELECT select_options
EXPLAIN tbl_name is a synonym for DESCRIBE tbl_name or
SHOW COLUMNS FROM tbl_name.
When you precede a SELECT statement with the keyword EXPLAIN,
MySQL explains how it would process the SELECT, providing
information about how tables are joined and in which order.
With the help of EXPLAIN, you can see when you must add indexes
to tables to get a faster SELECT that uses indexes to find the
records. You can also see if the optimizer joins the tables in an optimal
order. To force the optimizer to use a specific join order for a
SELECT statement, add a STRAIGHT_JOIN clause.
For non-simple joins, EXPLAIN returns a row of information for each
table used in the SELECT statement. The tables are listed in the order
they would be read. MySQL resolves all joins using a single-sweep
multi-join method. This means that MySQL reads a row from the first
table, then finds a matching row in the second table, then in the third table
and so on. When all tables are processed, it outputs the selected columns and
backtracks through the table list until a table is found for which there are
more matching rows. The next row is read from this table and the process
continues with the next table.
Output from EXPLAIN includes the following columns:
table
type
possible_keys
possible_keys column indicates which indexes MySQL
could use to find the rows in this table. Note that this column is
totally independent of the order of the tables. That means that some of
the keys in possible_keys may not be usable in practice with the
generated table order.
If this column is empty, there are no relevant indexes. In this case,
you may be able to improve the performance of your query by examining
the WHERE clause to see if it refers to some column or columns
that would be suitable for indexing. If so, create an appropriate index
and check the query with EXPLAIN again. See section 7.8 ALTER TABLE Syntax.
To see what indexes a table has, use SHOW INDEX FROM tbl_name.
key
key column indicates the key that MySQL actually
decided to use. The key is NULL if no index was chosen. If
MySQL chooses the wrong index, you can probably force
MySQL to use another index by using myisamchk --analyze,
See section 15.1.1 myisamchk Invocation Syntax, or by using USE INDEX/IGNORE INDEX.
See section 7.20 JOIN Syntax.
key_len
key_len column indicates the length of the key that
MySQL decided to use. The length is NULL if the
key is NULL. Note that this tells us how many parts of a
multi-part key MySQL will actually use.
ref
ref column shows which columns or constants are used with the
key to select rows from the table.
rows
rows column indicates the number of rows MySQL
believes it must examine to execute the query.
Extra
Distinct
Not exists
LEFT JOIN optimization on the
query and will not examine more rows in this table for a row combination
after it finds one row that matches the LEFT JOIN criteria.
range checked for each record (index map: #)Using filesort
join type and storing the sort key + pointer to
the row for all rows that match the WHERE. Then the keys are
sorted. Finally the rows are retrieved in sorted order.
Using index
Using temporary
ORDER BY on a different column set than you did a GROUP
BY on.
Where used
WHERE clause will be used to restrict which rows will be
matched against the next table or sent to the client. If you don't have
this information and the table is of type ALL or index,
you may have something wrong in your query (if you don't intend to
fetch/examine all rows from the table).
Using filesort and Using temporary.
The different join types are listed below, ordered from best to worst type:
system
const join type.
const
const tables are very fast as they are read only once!
eq_ref
const types. It is used when all parts of an index are used by
the join and the index is UNIQUE or a PRIMARY KEY.
ref
ref is used if the join
uses only a leftmost prefix of the key, or if the key is not UNIQUE
or a PRIMARY KEY (in other words, if the join cannot select a single
row based on the key value). If the key that is used matches only a few rows,
this join type is good.
range
key column indicates which index is used.
The key_len contains the longest key part that was used.
The ref column will be NULL for this type.
index
ALL, except that only the index tree is
scanned. This is usually faster than ALL, as the index file is usually
smaller than the data file.
ALL
const, and usually very bad in all other
cases. You normally can avoid ALL by adding more indexes, so that
the row can be retrieved based on constant values or column values from
earlier tables.
You can get a good indication of how good a join is by multiplying all values
in the rows column of the EXPLAIN output. This should tell you
roughly how many rows MySQL must examine to execute the query. This
number is also used when you restrict queries with the max_join_size
variable.
See section 12.2.3 Tuning Server Parameters.
The following example shows how a JOIN can be optimized progressively
using the information provided by EXPLAIN.
Suppose you have the SELECT statement shown below, that you examine
using EXPLAIN:
EXPLAIN SELECT tt.TicketNumber, tt.TimeIn,
tt.ProjectReference, tt.EstimatedShipDate,
tt.ActualShipDate, tt.ClientID,
tt.ServiceCodes, tt.RepetitiveID,
tt.CurrentProcess, tt.CurrentDPPerson,
tt.RecordVolume, tt.DPPrinted, et.COUNTRY,
et_1.COUNTRY, do.CUSTNAME
FROM tt, et, et AS et_1, do
WHERE tt.SubmitTime IS NULL
AND tt.ActualPC = et.EMPLOYID
AND tt.AssignedPC = et_1.EMPLOYID
AND tt.ClientID = do.CUSTNMBR;
For this example, assume that:
| Table | Column | Column type |
tt | ActualPC | CHAR(10)
|
tt | AssignedPC | CHAR(10)
|
tt | ClientID | CHAR(10)
|
et | EMPLOYID | CHAR(15)
|
do | CUSTNMBR | CHAR(15)
|
| Table | Index |
tt | ActualPC
|
tt | AssignedPC
|
tt | ClientID
|
et | EMPLOYID (primary key)
|
do | CUSTNMBR (primary key)
|
tt.ActualPC values aren't evenly distributed.
Initially, before any optimizations have been performed, the EXPLAIN
statement produces the following information:
table type possible_keys key key_len ref rows Extra
et ALL PRIMARY NULL NULL NULL 74
do ALL PRIMARY NULL NULL NULL 2135
et_1 ALL PRIMARY NULL NULL NULL 74
tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872
range checked for each record (key map: 35)
Because type is ALL for each table, this output indicates that
MySQL is doing a full join for all tables! This will take quite a
long time, as the product of the number of rows in each table must be
examined! For the case at hand, this is 74 * 2135 * 74 * 3872 =
45,268,558,720 rows. If the tables were bigger, you can only imagine how
long it would take.
One problem here is that MySQL can't (yet) use indexes on columns
efficiently if they are declared differently. In this context,
VARCHAR and CHAR are the same unless they are declared as
different lengths. Because tt.ActualPC is declared as CHAR(10)
and et.EMPLOYID is declared as CHAR(15), there is a length
mismatch.
To fix this disparity between column lengths, use ALTER TABLE to
lengthen ActualPC from 10 characters to 15 characters:
mysql> ALTER TABLE tt MODIFY ActualPC VARCHAR(15);
Now tt.ActualPC and et.EMPLOYID are both VARCHAR(15).
Executing the EXPLAIN statement again produces this result:
table type possible_keys key key_len ref rows Extra
tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used
do ALL PRIMARY NULL NULL NULL 2135
range checked for each record (key map: 1)
et_1 ALL PRIMARY NULL NULL NULL 74
range checked for each record (key map: 1)
et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1
This is not perfect, but is much better (the product of the rows
values is now less by a factor of 74). This version is executed in a couple
of seconds.
A second alteration can be made to eliminate the column length mismatches
for the tt.AssignedPC = et_1.EMPLOYID and tt.ClientID =
do.CUSTNMBR comparisons:
mysql> ALTER TABLE tt MODIFY AssignedPC VARCHAR(15),
MODIFY ClientID VARCHAR(15);
Now EXPLAIN produces the output shown below:
table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 tt ref AssignedPC,ClientID,ActualPC ActualPC 15 et.EMPLOYID 52 where used et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
This is almost as good as it can get.
The remaining problem is that, by default, MySQL assumes that values
in the tt.ActualPC column are evenly distributed, and that isn't the
case for the tt table. Fortunately, it is easy to tell MySQL
about this:
shell> myisamchk --analyze PATH_TO_MYSQL_DATABASE/tt shell> mysqladmin refresh
Now the join is perfect, and EXPLAIN produces this result:
table type possible_keys key key_len ref rows Extra tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1 et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1
Note that the rows column in the output from EXPLAIN is an
educated guess from the MySQL join optimizer. To optimize a
query, you should check if the numbers are even close to the truth. If not,
you may get better performance by using STRAIGHT_JOIN in your
SELECT statement and trying to list the tables in a different order in
the FROM clause.
DESCRIBE Syntax (Get Information About Columns)
{DESCRIBE | DESC} tbl_name {col_name | wild}
DESCRIBE provides information about a table's columns. col_name
may be a column name or a string containing the SQL `%' and `_'
wild-card characters.
If the column types are different than you expect them to be based on a
CREATE TABLE statement, note that MySQL sometimes
changes column types. See section 7.7.1 Silent Column Specification Changes.
This statement is provided for Oracle compatibility.
The SHOW statement provides similar information.
See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
BEGIN/COMMIT/ROLLBACK Syntax
By default, MySQL runs in autocommit mode. This means that
as soon as you execute an update, MySQL will store the update on
disk.
If you are using BDB tables, you can put MySQL into
non-autocommit mode with the following command:
SET AUTOCOMMIT=0
After this you must use COMMIT to store your changes to disk or
ROLLBACK if you want to ignore the changes you have made since
the beginning of your transaction.
If you want to switch from AUTOCOMMIT mode for one series of
statements, you can use the BEGIN or BEGIN WORK statement:
BEGIN; SELECT @A:=SUM(salary) FROM table1 WHERE type=1; UPDATE table2 SET summmary=@A WHERE type=1; COMMIT;
Note that if you are using non-transaction-safe tables, the changes will be
stored at once, independent of the status of the autocommit mode.
If you do a ROLLBACK when you have updated a non-transactional
table you will get an error (ER_WARNING_NOT_COMPLETE_ROLLBACK) as
a warning. All transactional safe tables will be restored but any
non-transactional table will not change.
If you are using BEGIN or SET AUTO_COMMIT=0, you
should use the MySQL binary log for backups instead of the
old update log; The transaction is stored in the binary log
in one chunk, during COMMIT, the to ensure and ROLLBACK:ed
transactions are not stored. See section 21.4 The Binary Log.
The following commands automaticly ends an transaction (as if you had done
a COMMIT before executing the command):
ALTER TABLE | BEGIN | CREATE INDEX
|
DROP DATABASE | DROP TABLE | RENAME TABLE
|
TRUNCATE
|
LOCK TABLES/UNLOCK TABLES Syntax
LOCK TABLES tbl_name [AS alias] {READ | [READ LOCAL] | [LOW_PRIORITY] WRITE}
[, tbl_name {READ | [LOW_PRIORITY] WRITE} ...]
...
UNLOCK TABLES
LOCK TABLES locks tables for the current thread. UNLOCK
TABLES releases any locks held by the current thread. All tables that
are locked by the current thread are automatically unlocked when the
thread issues another LOCK TABLES, or when the connection to the
server is closed.
If a thread obtains a READ lock on a table, that thread (and all other
threads) can only read from the table. If a thread obtains a WRITE
lock on a table, then only the thread holding the lock can READ from
or WRITE to the table. Other threads are blocked.
The difference between READ LOCAL and READ is that
READ LOCAL allows non-conflicting INSERT statements to
execute while the lock is held. This can't however be used if you are
going to manipulate the database files outside MySQL while you
hold the lock.
Each thread waits (without timing out) until it obtains all the locks it has requested.
WRITE locks normally have higher priority than READ locks, to
ensure that updates are processed as soon as possible. This means that if one
thread obtains a READ lock and then another thread requests a
WRITE lock, subsequent READ lock requests will wait until the
WRITE thread has gotten the lock and released it. You can use
LOW_PRIORITY WRITE locks to allow other threads to obtain READ
locks while the thread is waiting for the WRITE lock. You should only
use LOW_PRIORITY WRITE locks if you are sure that there will
eventually be a time when no threads will have a READ lock.
When you use LOCK TABLES, you must lock all tables that you are
going to use and you must use the same alias that you are going to use
in your queries! If you are using a table multiple times in a query
(with aliases), you must get a lock for each alias! This policy ensures
that table locking is deadlock free andh makes the locking code smaller,
simpler and much faster.
Note that you should NOT lock any tables that you are using with
INSERT DELAYED. This is because that in this case the INSERT
is done by a separate thread.
Normally, you don't have to lock tables, as all single UPDATE statements
are atomic; no other thread can interfere with any other currently executing
SQL statement. There are a few cases when you would like to lock tables
anyway:
READ-locked table and no other
thread can read a WRITE-locked table.
LOCK TABES if you want to ensure that no other thread comes between a
SELECT and an UPDATE. The example shown below
requires LOCK TABLES in order to execute safely:
mysql> LOCK TABLES trans READ, customer WRITE;
mysql> select sum(value) from trans where customer_id= some_id;
mysql> update customer set total_value=sum_from_previous_statement
where customer_id=some_id;
mysql> UNLOCK TABLES;
Without LOCK TABLES, there is a chance that another thread might
insert a new row in the trans table between execution of the
SELECT and UPDATE statements.
By using incremental updates (UPDATE customer SET
value=value+new_value) or the LAST_INSERT_ID() function, you can
avoid using LOCK TABLES in many cases.
You can also solve some cases by using the user-level lock functions
GET_LOCK() and RELEASE_LOCK(). These locks are saved in a hash
table in the server and implemented with pthread_mutex_lock() and
pthread_mutex_unlock() for high speed.
See section 7.4.12 Miscellaneous Functions.
See section 12.2.8 How MySQL Locks Tables, for more information on locking policy.
You can also lock all tables in all databases with read locks with the
FLUSH TABLES WITH READ LOCK command. See section 7.26 FLUSH Syntax (Clearing Caches). This is very
convinient way to get backups if you have a file system, like Veritas,
that can take snapshots in time.
SET SyntaxSET [OPTION] SQL_VALUE_OPTION= value, ...
SET OPTION sets various options that affect the operation of the
server or your client. Any option you set remains in effect until the
current session ends, or until you set the option to a different value.
CHARACTER SET character_set_name | DEFAULT
character_set_name is
cp1251_koi8, but you can easily add new mappings by editing the
`sql/convert.cc' file in the MySQL source distribution. The
default mapping can be restored by using a character_set_name value of
DEFAULT.
Note that the syntax for setting the CHARACTER SET option differs
from the syntax for setting the other options.
PASSWORD = PASSWORD('some password')
PASSWORD FOR user = PASSWORD('some password')
mysql database can do this. The user should be
given in user@hostname format, where user and hostname
are exactly as they are listed in the User and Host columns of
the mysql.user table entry. For example, if you had an entry with
User and Host fields of 'bob' and '%.loc.gov',
you would write:
mysql> SET PASSWORD FOR bob@"%.loc.gov" = PASSWORD("newpass");
or
mysql> UPDATE mysql.user SET password=PASSWORD("newpass") where user="bob' and host="%.loc.gov";
SQL_AUTO_IS_NULL = 0 | 1
1 (default) then one can find the last inserted row
for a table with an auto_increment row with the following construct:
WHERE auto_increment_column IS NULL. This is used by some
ODBC programs like Access.
AUTOCOMMIT= 0 | 1
1 all changes to a table will be done at once. To start
a multi-command transaction, you have to use the BEGIN
statement. See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax. If set to 0 you have to use COMMIT /
ROLLBACK to accept/revoke that transaction. See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax. Note
that when you change from not AUTOCOMMIT mode to
AUTOCOMMIT mode, MySQL will do an automatic
COMMIT on any open transactions.
SQL_BIG_TABLES = 0 | 1
1, all temporary tables are stored on disk rather than in
memory. This will be a little slower, but you will not get the error
The table tbl_name is full for big SELECT operations that
require a large temporary table. The default value for a new connection is
0 (that is, use in-memory temporary tables).
SQL_BIG_SELECTS = 0 | 1
0, MySQL will abort if a SELECT is attempted
that probably will take a very long time. This is useful when an inadvisable
WHERE statement has been issued. A big query is defined as a
SELECT that probably will have to examine more than
max_join_size rows. The default value for a new connection is
1 (which will allow all SELECT statements).
SQL_BUFFER_RESULT = 0 | 1
SQL_BUFFER_RESULT will force the result from SELECT's
to be put into a temporary table. This will help MySQL free the
table locks early and will help in cases where it takes a long time to
send the result set to the client.
SQL_LOW_PRIORITY_UPDATES = 0 | 1
1, all INSERT, UPDATE, DELETE, and
and LOCK TABLE WRITE statements wait until there is no pending
SELECT or LOCK TABLE READ on the affected table.
SQL_MAX_JOIN_SIZE = value | DEFAULT
SELECTs that will probably need to examine more than
value row combinations. By setting this value, you can catch
SELECTs where keys are not used properly and that would probably
take a long time. Setting this to a value other than DEFAULT will reset
the SQL_BIG_SELECTS flag. If you set the SQL_BIG_SELECTS
flag again, the SQL_MAX_JOIN_SIZE variable will be ignored.
You can set a default value for this variable by starting mysqld with
-O max_join_size=#.
SQL_SAFE_MODE = 0 | 1
1, MySQL will abort if an UPDATE or
DELETE is attempted that doesn't use a key or LIMIT in the
WHERE clause. This makes it possible to catch wrong updates
when creating SQL commands by hand.
SQL_SELECT_LIMIT = value | DEFAULT
SELECT statements. If
a SELECT has a LIMIT clause, the LIMIT takes precedence
over the value of SQL_SELECT_LIMIT. The default value for a new
connection is ``unlimited.'' If you have changed the limit, the default value
can be restored by using a SQL_SELECT_LIMIT value of DEFAULT.
SQL_LOG_OFF = 0 | 1
1, no logging will be done to the standard log for this
client, if the client has the process privilege. This does not
affect the update log!
SQL_LOG_UPDATE = 0 | 1
0, no logging will be done to the update log for the client,
if the client has the process privilege. This does not affect the
standard log!
SQL_QUOTE_SHOW_CREATE = 0 | 1
1, SHOW CREATE TABLE will quote
table and column names. This is on by default,
for replication of tables with fancy column names to work.
section 7.28.8 SHOW CREATE TABLE.
TIMESTAMP = timestamp_value | DEFAULT
LAST_INSERT_ID = #
LAST_INSERT_ID(). This is stored in
the update log when you use LAST_INSERT_ID() in a command that updates
a table.
INSERT_ID = #
INSERT or ALTER TABLE
command when inserting an AUTO_INCREMENT value. This is mainly used
with the update log.
GRANT and REVOKE Syntax
GRANT priv_type [(column_list)] [, priv_type [(column_list)] ...]
ON {tbl_name | * | *.* | db_name.*}
TO user_name [IDENTIFIED BY 'password']
[, user_name [IDENTIFIED BY 'password'] ...]
[WITH GRANT OPTION]
REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...]
ON {tbl_name | * | *.* | db_name.*}
FROM user_name [, user_name ...]
GRANT is implemented in MySQL Version 3.22.11 or later. For
earlier MySQL versions, the GRANT statement does nothing.
The GRANT and REVOKE commands allow system administrators to
grant and revoke rights to MySQL users at four privilege levels:
mysql.user table.
mysql.db and mysql.host tables.
mysql.tables_priv table.
mysql.columns_priv table.
For examples of how GRANT works, see section 6.13 Adding New User Privileges to MySQL.
For the GRANT and REVOKE statements, priv_type may be
specified as any of the following:
ALL PRIVILEGES FILE RELOAD ALTER INDEX SELECT CREATE INSERT SHUTDOWN DELETE PROCESS UPDATE DROP REFERENCES USAGE
ALL is a synonym for ALL PRIVILEGES. REFERENCES is not
yet implemented. USAGE is currently a synonym for ``no privileges.''
It can be used when you want to create a user that has no privileges.
To revoke the grant privilege from a user, use a priv_type
value of GRANT OPTION:
REVOKE GRANT OPTION ON ... FROM ...;
The only priv_type values you can specify for a table are SELECT,
INSERT, UPDATE, DELETE, CREATE, DROP,
GRANT, INDEX, and ALTER.
The only priv_type values you can specify for a column (that is, when
you use a column_list clause) are SELECT, INSERT, and
UPDATE.
You can set global privileges by using ON *.* syntax. You can set
database privileges by using ON db_name.* syntax. If you specify
ON * and you have a current database, you will set the privileges for
that database. (WARNING: If you specify ON * and you
don't have a current database, you will affect the global privileges!)
In order to accommodate granting rights to users from arbitrary hosts,
MySQL supports specifying the user_name value in the form
user@host. If you want to specify a user string
containing special characters (such as `-'), or a host string
containing special characters or wild-card characters (such as `%'), you
can quote the user or host name (for example, 'test-user'@'test-hostname').
You can specify wild cards in the hostname. For example,
user@"%.loc.gov" applies to user for any host in the
loc.gov domain, and user@"144.155.166.%" applies to user
for any host in the 144.155.166 class C subnet.
The simple form user is a synonym for user@"%".
NOTE: If you allow anonymous users to connect to the MySQL
server (which is the default), you should also add all local users as
user@localhost because otherwise the anonymous user entry for the
local host in the mysql.user table will be used when the user tries to
log into the MySQL server from the local machine! Anonymous users
are defined by inserting entries with User='' into the
mysql.user table. You can verify if this applies to you by executing
this query:
mysql> SELECT Host,User FROM mysql.user WHERE User='';
For the moment, GRANT only supports host, table, database, and
column names up to 60 characters long. A user name can be up to 16
characters.
The privileges for a table or column are formed from the
logical OR of the privileges at each of the four privilege
levels. For example, if the mysql.user table specifies that a
user has a global select privilege, this can't be denied by an
entry at the database, table, or column level.
The privileges for a column can be calculated as follows:
global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges
In most cases, you grant rights to a user at only one of the privilege levels, so life isn't normally as complicated as above. The details of the privilege-checking procedure are presented in section 6 The MySQL Access Privilege System.
If you grant privileges for a user/hostname combination that does not exist
in the mysql.user table, an entry is added and remains there until
deleted with a DELETE command. In other words, GRANT may
create user table entries, but REVOKE will not remove them;
you must do that explicitly using DELETE.
In MySQL Version 3.22.12 or later,
if a new user is created or if you have global grant privileges, the user's
password will be set to the password specified by the IDENTIFIED BY
clause, if one is given. If the user already had a password, it is replaced
by the new one.
WARNING: If you create a new user but do not specify an
IDENTIFIED BY clause, the user has no password. This is insecure.
Passwords can also be set with the SET PASSWORD command.
See section 7.33 SET Syntax.
If you grant privileges for a database, an entry in the mysql.db
table is created if needed. When all privileges for the database have been
removed with REVOKE, this entry is deleted.
If a user doesn't have any privileges on a table, the table is not displayed
when the user requests a list of tables (for example, with a SHOW TABLES
statement).
The WITH GRANT OPTION clause gives the user the ability to give
to other users any privileges the user has at the specified privilege level.
You should be careful to whom you give the grant privilege, as two
users with different privileges may be able to join privileges!
You cannot grant another user a privilege you don't have yourself; the grant privilege allows you to give away only those privileges you possess.
Be aware that when you grant a user the grant privilege at a
particular privilege level, any privileges the user already possesses (or
is given in the future!) at that level are also grantable by that user.
Suppose you grant a user the insert privilege on a database. If
you then grant the select privilege on the database and specify
WITH GRANT OPTION, the user can give away not only the select
privilege, but also insert. If you then grant the update
privilege to the user on the database, the user can give away the
insert, select and update.
You should not grant alter privileges to a normal user. If you do that, the user can try to subvert the privilege system by renaming tables!
Note that if you are using table or column privileges for even one user, the server examines table and column privileges for all users and this will slow down MySQL a bit.
When mysqld starts, all privileges are read into memory.
Database, table, and column privileges take effect at once, and
user-level privileges take effect the next time the user connects.
Modifications to the grant tables that you perform using GRANT or
REVOKE are noticed by the server immediately.
If you modify the grant tables manually (using INSERT, UPDATE,
etc.), you should execute a FLUSH PRIVILEGES statement or run
mysqladmin flush-privileges to tell the server to reload the grant
tables.
See section 6.11 When Privilege Changes Take Effect.
The biggest differences between the ANSI SQL and MySQL versions of
GRANT are:
TRIGGER, EXECUTE or
UNDER privileges.
MySQL have the INSERT grant on only part of the
columns in a table, you can execute INSERT statements on the
table; The columns for which you don't have the INSERT privilege
will set to their default values. ANSI SQL requires you to have the
INSERT privilege on all columns.
REVOKE commands or by manipulating the
MySQL grant tables.
CREATE INDEX SyntaxCREATE [UNIQUE|FULLTEXT] INDEX index_name ON tbl_name (col_name[(length)],... )
The CREATE INDEX statement doesn't do anything in MySQL prior
to Version 3.22. In Version 3.22 or later, CREATE INDEX is mapped to an
ALTER TABLE statement to create indexes.
See section 7.8 ALTER TABLE Syntax.
Normally, you create all indexes on a table at the time the table itself
is created with CREATE TABLE.
See section 7.7 CREATE TABLE Syntax.
CREATE INDEX allows you to add indexes to existing tables.
A column list of the form (col1,col2,...) creates a multiple-column
index. Index values are formed by concatenating the values of the given
columns.
For CHAR and VARCHAR columns, indexes can be created that
use only part of a column, using col_name(length) syntax. (On
BLOB and TEXT columns the length is required). The
statement shown below creates an index using the first 10 characters of
the name column:
mysql> CREATE INDEX part_of_name ON customer (name(10));
Because most names usually differ in the first 10 characters, this index should
not be much slower than an index created from the entire name column.
Also, using partial columns for indexes can make the index file much smaller,
which could save a lot of disk space and might also speed up INSERT
operations!
Note that you can only add an index on a column that can have NULL
values or on a BLOB/TEXT column if you are using
MySQL Version 3.23.2 or newer and are using the MyISAM
table type.
For more information about how MySQL uses indexes, see section 12.4 How MySQL Uses Indexes.
FULLTEXT indexes can index only VARCHAR and
TEXT columns, and only in MyISAM tables. FULLTEXT indexes
are available in MySQL Version 3.23.23 and later.
section 24.2 MySQL Full-text Search.
DROP INDEX SyntaxDROP INDEX index_name ON tbl_name
DROP INDEX drops the index named index_name from the table
tbl_name. DROP INDEX doesn't do anything in MySQL
prior to Version 3.22. In Version 3.22 or later, DROP INDEX is mapped to an
ALTER TABLE statement to drop the index.
See section 7.8 ALTER TABLE Syntax.
The MySQL server supports the # to end of line, --
to end of line and /* in-line or multiple-line */ comment
styles:
mysql> select 1+1; # This comment continues to the end of line mysql> select 1+1; -- This comment continues to the end of line mysql> select 1 /* this is an in-line comment */ + 1; mysql> select 1+ /* this is a multiple-line comment */ 1;
Note that the -- comment style requires you to have at least one space
after the --!
Although the server understands the comment syntax just described,
there are some limitations on the way that the mysql client
parses /* ... */ comments:
mysql interactively, you can tell that it
has gotten confused like this because the prompt changes from mysql>
to '> or ">.
These limitations apply both when you run mysql interactively
and when you put commands in a file and tell mysql to read its
input from that file with mysql < some-file.
MySQL doesn't support the `--' ANSI SQL comment style. See section 5.4.7 `--' as the Start of a Comment.
CREATE FUNCTION/DROP FUNCTION Syntax
CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER}
SONAME shared_library_name
DROP FUNCTION function_name
A user-definable function (UDF) is a way to extend MySQL with a new
function that works like native (built in) MySQL functions such as
ABS() and CONCAT().
AGGREGATE is a new option for MySQL Version 3.23. An
AGGREGATE function works exactly like a native MySQL
GROUP function like SUM or COUNT().
CREATE FUNCTION saves the function's name, type, and shared library
name in the mysql.func system table. You must have the
insert and delete privileges for the mysql database
to create and drop functions.
All active functions are reloaded each time the server starts, unless
you start mysqld with the --skip-grant-tables option. In
this case, UDF initialization is skipped and UDFs are unavailable.
(An active function is one that has been loaded with CREATE FUNCTION
and not removed with DROP FUNCTION.)
For instructions on writing user-definable functions, see section 16 Adding New Functions to MySQL. For the UDF mechanism to work, functions must be written in C or
C++, your operating system must support dynamic loading and you must have
compiled mysqld dynamically (not statically).
A common problem stems from trying to create a table with column names that
use the names of datatypes or functions built into MySQL, such as
TIMESTAMP or GROUP. You're allowed to do it (for example,
ABS is an allowed column name), but whitespace is not allowed between
a function name and the `(' when using functions whose names are also
column names.
The following words are explicitly reserved in MySQL. Most of
them are forbidden by ANSI SQL92 as column and/or table names
(for example, group).
A few are reserved because MySQL needs them and is
(currently) using a yacc parser:
action | add | aggregate | all
|
alter | after | and | as
|
asc | avg | avg_row_length | auto_increment
|
between | bigint | bit | binary
|
blob | bool | both | by
|
cascade | case | char | character
|
change | check | checksum | column
|
columns | comment | constraint | create
|
cross | current_date | current_time | current_timestamp
|
data | database | databases | date
|
datetime | day | day_hour | day_minute
|
day_second | dayofmonth | dayofweek | dayofyear
|
dec | decimal | default | delayed
|
delay_key_write | delete | desc | describe
|
distinct | distinctrow | double | drop
|
end | else | escape | escaped
|
enclosed | enum | explain | exists
|
fields | file | first | float
|
float4 | float8 | flush | foreign
|
from | for | full | function
|
global | grant | grants | group
|
having | heap | high_priority | hour
|
hour_minute | hour_second | hosts | identified
|
ignore | in | index | infile
|
inner | insert | insert_id | int
|
integer | interval | int1 | int2
|
int3 | int4 | int8 | into
|
if | is | isam | join
|
key | keys | kill | last_insert_id
|
leading | left | length | like
|
lines | limit | load | local
|
lock | logs | long | longblob
|
longtext | low_priority | max | max_rows
|
match | mediumblob | mediumtext | mediumint
|
middleint | min_rows | minute | minute_second
|
modify | month | monthname | myisam
|
natural | numeric | no | not
|
null | on | optimize | option
|
optionally | or | order | outer
|
outfile | pack_keys | partial | password
|
precision | primary | procedure | process
|
processlist | privileges | read | real
|
references | reload | regexp | rename
|
replace | restrict | returns | revoke
|
rlike | row | rows | second
|
select | set | show | shutdown
|
smallint | soname | sql_big_tables | sql_big_selects
|
sql_low_priority_updates | sql_log_off | sql_log_update | sql_select_limit
|
sql_small_result | sql_big_result | sql_warnings | straight_join
|
starting | status | string | table
|
tables | temporary | terminated | text
|
then | time | timestamp | tinyblob
|
tinytext | tinyint | trailing | to
|
type | use | using | unique
|
unlock | unsigned | update | usage
|
values | varchar | variables | varying
|
varbinary | with | write | when
|
where | year | year_month | zerofill
|
The following symbols (from the table above) are disallowed by ANSI SQL but allowed by MySQL as column/table names. This is because some of these names are very natural names and a lot of people have already used them.
ACTION
BIT
DATE
ENUM
NO
TEXT
TIME
TIMESTAMP
As of MySQL Version 3.23.6, you can choose between three basic
table formats. When you create a new table, you can tell MySQL
which table type it should use for the table. MySQL will
always create a .frm file to hold the table and column
definitions. Depending on the table type, the index and data will be
stored in other files.
The default table type in MySQL is MyISAM. If you are
trying to use a table type that is not incompiled or activated,
MySQL will instead create a table of type MyISAM.
You can convert tables between different types with the ALTER
TABLE statement. See section 7.8 ALTER TABLE Syntax.
Note that MySQL supports two different kinds of
tables. Transaction-safe tables (BDB) and not transaction-safe
tables (ISAM, MERGE, MyISAM, and HEAP).
Advantages of transaction-safe tables (TST):
COMMIT command.
ROLLBACK to ignore your changes (if you are not
running in auto commit mode).
Advantages of not transaction-safe tables (NTST):
You can combine TST and NTST tables in the same statements to get the best of both worlds.
MyISAM is the default table type in MySQL Version 3.23. It's
based on the ISAM code and has a lot of useful extensions.
The index is stored in a file with the .MYI (MYIndex) extension,
and the data is stored in a file with the .MYD (MYData) extension.
You can check/repair MyISAM tables with the myisamchk
utility. See section 15.4 Using myisamchk for Crash Recovery.
The following is new in MyISAM:
mysqld is started with --myisam-recover, MyISAM tables
will automaticly be repaired on open if the table wasn't closed properly.
INSERT new rows in a table without deleted rows,
while other threads are reading from the table.
AUTO_INCREMENT column. MyISAM
will automatically update this on INSERT/UPDATE. The
AUTO_INCREMENT value can be reset with myisamchk. This
will make AUTO_INCREMENT columns faster (at least 10 %) and old
numbers will not be reused as with the old ISAM. Note that when an
AUTO_INCREMENT is defined on the end of a multi-part-key the old
behavior is still present.
AUTO_INCREMENT
column) the key tree will be split so that the high node only contains one
key. This will improve the space utilization in the key tree.
BLOB and TEXT columns can be indexed.
NULL values are allowed in indexed columns. This takes 0-1
bytes/key.
myisamchk.
MyISAM file that indicates whether or not the
table was closed correctly. This will soon be used for automatic repair
in the MySQL server.
myisamchk will mark tables as checked if one runs it with
--update-state. myisamchk --fast will only check those
tables that don't have this mark.
myisamchk -a stores statistics for key parts (and not only for
whole keys as in ISAM).
myisampack can pack BLOB and VARCHAR columns.
MyISAM also supports the following things, which MySQL
will be able to use in the near future:
VARCHAR type; A VARCHAR column starts
with a length stored in 2 bytes.
VARCHAR may have fixed or dynamic record length.
VARCHAR and CHAR may be up to 64K.
All key segments have their own language definition. This will enable
MySQL to have different language definitions per column.
UNIQUE. This will allow
you to have UNIQUE on any combination of columns in a table. (You
can't search on a UNIQUE computed index, however.)
Note that index files are usually much smaller with MyISAM than with
ISAM. This means that MyISAM will normally use less
system resources than ISAM, but will need more CPU when inserting
data into a compressed index.
The following options to mysqld can be used to change the behavior of
MyISAM tables:
| Option | Meaning |
--myisam-recover=# | Automatic recover of crashed tables. |
-O myisam_sort_buffer_size=# | Buffer used when recovering tables. |
--delay-key-write-for-all-tables | Don't flush key buffers between writes for any MyISAM table |
The automatic recovery is activated if you start mysqld with
--myisam-recover=#. See section 4.16.4 Command-line Options.
On open, the table is checked if it's marked as crashed or if the open
count variable for the table is not 0 and you are running with
--skip-locking. If either of the above is true the following happens.
If the recover wouldn't be able to recover all rows from a previous
completed statement and you didn't specify FORCE as an option to
myisam-recover, then the automatic repair will abort with an error
message in the error file:
Error: Couldn't repair table: test.g00pages
If you in this case had used the FORCE option you would instead have got
a warning in the error file:
Warning: Found 344 of 354 rows when repairing ./test/g00pages
Note that if you run automatic recover with the BACKUP option,
you should have a cron script that automaticly moves file with names
like `tablename-datetime.BAK' from the database directories to a
backup media.
See section 4.16.4 Command-line Options.
MySQL can support different index types, but the normal type is
ISAM or MyISAM. These use a B-tree index, and you can roughly calculate
the size for the index file as (key_length+4)/0.67, summed over
all keys. (This is for the worst case when all keys are inserted in
sorted order and we don't have any compressed keys.)
String indexes are space compressed. If the first index part is a
string, it will also be prefix compressed. Space compression makes the
index file smaller than the above figures if the string column has a lot
of trailing space or is a VARCHAR column that is not always used
to the full length. Prefix compression is used on keys that start
with a string. Prefix compression helps if there are many strings
with an identical prefix.
In MyISAM tables, you can also prefix compress numbers by specifying
PACK_KEYS=1 when you create the table. This helps when you have
many integer keys that have an identical prefix when the numbers are stored
high-byte first.
MyISAM supports 3 different table types. Two of them are chosen
automatically depending on the type of columns you are using. The third,
compressed tables, can only be created with the myisampack tool.
This is the default format. It's used when the table contains no
VARCHAR, BLOB, or TEXT columns.
This format is the simplest and most secure format. It is also the fastest of the on-disk formats. The speed comes from the easy way data can be found on disk. When looking up something with an index and static format it is very simple. Just multiply the row number by the row length.
Also, when scanning a table it is very easy to read a constant number of records with each disk read.
The security is evidenced if your computer crashes when writing to a
fixed-size MyISAM file, in which case myisamchk can easily figure out where each
row starts and ends. So it can usually reclaim all records except the
partially written one. Note that in MySQL all indexes can always be
reconstructed:
CHAR, NUMERIC, and DECIMAL columns are space-padded
to the column width.
myisamchk) unless a huge number of
records are deleted and you want to return free disk space to the operating
system.
This format is used if the table contains any VARCHAR, BLOB,
or TEXT columns or if the table was created with
ROW_FORMAT=dynamic.
This format is a litte more complex because each row has to have a header that says how long it is. One record can also end up at more than one location when it is made longer at an update.
You can use OPTIMIZE table or myisamchk to defragment a
table. If you have static data that you access/change a lot in the same
table as some VARCHAR or BLOB columns, it might be a good
idea to move the dynamic columns to other tables just to avoid
fragmentation:
'') for string columns, or zero for numeric columns. (This isn't
the same as columns containing NULL values.) If a string column
has a length of zero after removal of trailing spaces, or a numeric
column has a value of zero, it is marked in the bit map and not saved to
disk. Non-empty strings are saved as a length byte plus the string
contents.
myisamchk
-r from time to time to get better performance. Use myisamchk -ei
tbl_name for some statistics.
3 + (number of columns + 7) / 8 + (number of char columns) + packed size of numeric columns + length of strings + (number of NULL columns + 7) / 8There is a penalty of 6 bytes for each link. A dynamic record is linked whenever an update causes an enlargement of the record. Each new link will be at least 20 bytes, so the next enlargement will probably go in the same link. If not, there will be another link. You may check how many links there are with
myisamchk -ed. All links may be removed with myisamchk -r.
This is a read-only type that is generated with the optional
myisampack tool (pack_isam for ISAM tables):
myisampack.
0 are stored using 1 bit.
BIGINT column (8 bytes) may
be stored as a TINYINT column (1 byte) if all values are in the range
0 to 255.
ENUM.
BLOB or TEXT
columns.
myisamchk.
MERGE tables are new in MySQL Version 3.23.25. The code
is still in alpha, but should stabilize soon! The one thing that is
currently missing is a way for the SQL prompt to say which tables are
part of the MERGE table.
A MERGE table is a collection of identical MyISAM tables
that can be used as one. You can only SELECT, DELETE, and
UPDATE from the collection of tables. If you DROP the
MERGE table, you are only dropping the MERGE
specification.
With identical tables we mean that all tables are created with identical
column information. Some of the tables can be compressed with
myisampack. See section 14.10 The MySQL Compressed Read-only Table Generator.
When you create a MERGE table, you will get a .frm table
definition file and a .MRG table list file. The .MRG just
contains a list of the index files (.MYI files) that should
be used as one.
For the moment you need to have SELECT, UPDATE, and
DELETE privileges on the tables you map to a MERGE table.
MERGE tables can help you solve the following problems:
myisampack, and then create a MERGE to use these as one.
MERGE table on this could be much faster than using
the big table. (You can, of course, also use a RAID to get the same
kind of benefits.)
MERGE tables active, with possible overlapping files.
MERGE file than trying to repair a real big file.
MERGE table uses the
index of the individual tables. It doesn't need an index of its one.
This makes MERGE table collections VERY fast to make or remap.
MERGE table on them on demand.
This is much faster and will save a lot of disk space.
The disadvantages with MERGE tables are:
INSERT on MERGE tables, as MySQL can't know
in which of the tables we should insert the row.
MyISAM tables for a MERGE table.
MERGE tables uses more file descriptors. If you are using a
MERGE that maps over 10 tables and 10 users are using this, you
are using 10*10 + 10 file descriptors. (10 data files for 10 users
and 10 shared index files.)
MERGE
handler will need to issue a read on all underlying tables to check
which one most closely matches the given key. If you then do a 'read-next'
then the merge table handler will need to search the read buffers
to find the next key. Only when one key buffer is used up, the handler
will need to read the next key block. This makes MERGE keys much slower
on eq_ref searches, but not much slower on ref searches.
See section 7.29 EXPLAIN Syntax (Get Information About a SELECT).
MERGE table from within MySQL.
The following example shows you how to use MERGE tables:
CREATE TABLE t1 (a INT AUTO_INCREMENT PRIMARY KEY, message CHAR(20));
CREATE TABLE t2 (a INT AUTO_INCREMENT PRIMARY KEY, message CHAR(20));
INSERT INTO t1 (message) VALUES ("Testing"),("table"),("t1");
INSERT INTO t2 (message) VALUES ("Testing"),("table"),("t2");
CREATE TABLE total (a INT NOT NULL, message CHAR(20), KEY(a)) TYPE=MERGE UNION=(t1,t2);
Note that we didn't create a UNIQUE or PRIMARY KEY in the
total table as the key isn't going to be unique in the total
table.
Note that you can also manipulate the .MRG file directly from
the outside of the MySQL server:
shell> cd /mysql-data-directory/current-database shell> ls -1 t1.MYI t2.MYI > total.MRG
Now you can do things like:
mysql> select * from total; +---+---------+ | a | message | +---+---------+ | 1 | Testing | | 2 | table | | 3 | t1 | | 1 | Testing | | 2 | table | | 3 | t2 | +---+---------+
To remap a MERGE table you must either DROP it and
re-create it, use ALTER TABLE with a new UNION
specification, or change the .MRG file and issue a FLUSH
TABLE on the MERGE table and all underlying tables to force the
handler to read the new definition file.
You can also use the deprecated ISAM table type. This will disappear
rather soon because MyISAM is a better implementation of the same
thing. ISAM uses a B-tree index. The index is stored in a file
with the .ISM extension, and the data is stored in a file with the
.ISD extension. You can check/repair ISAM tables with the
isamchk utility. See section 15.4 Using myisamchk for Crash Recovery.
ISAM has the following features/properties:
Most of the things true for MyISAM tables are also true for ISAM
tables. See section 8.1 MyISAM Tables. The major differences compared to MyISAM
tables are:
pack_isam rather than with myisampack.
HEAP tables use a hashed index and are stored in memory. This
makes them very fast, but if MySQL crashes you will lose all
data stored in them. HEAP is very useful for temporary tables!
The MySQL internal HEAP tables use 100% dynamic hashing
without overflow areas. There is no extra space needed for free lists.
HEAP tables also don't have problems with delete + inserts, which
normally is common with hashed tables:
mysql> CREATE TABLE test TYPE=HEAP SELECT ip,SUM(downloads) as down
FROM log_table GROUP BY ip;
mysql> SELECT COUNT(ip),AVG(down) FROM test;
mysql> DROP TABLE test;
Here are some things you should consider when you use HEAP tables:
MAX_ROWS in the CREATE statement
to ensure that you accidently do not use all memory.
= and <=> (but are VERY fast).
HEAP tables can only use whole keys to search for a row; compare this
to MyISAM tables where any prefix of the key can be used to find rows.
HEAP tables use a fixed record length format.
HEAP doesn't support BLOB/TEXT columns.
HEAP doesn't support AUTO_INCREMENT columns.
HEAP doesn't support an index on a NULL column.
HEAP table (this isn't common for
hashed tables).
HEAP tables are shared between all clients (just like any other
table).
ORDER BY).
HEAP tables are allocated in small blocks. The tables
are 100% dynamic (on inserting). No overflow areas and no extra key
space are needed. Deleted rows are put in a linked list and are
reused when you insert new data into the table.
DELETE FROM heap_table,
TRUNCATE heap_table or DROP TABLE heap_table.
MyISAM
table to a HEAP table.
HEAP tables bigger than max_heap_table_size.
The memory needed for one row in a HEAP table is:
SUM_OVER_ALL_KEYS(max_length_of_key + sizeof(char*) * 2) + ALIGN(length_of_row+1, sizeof(char*))
sizeof(char*) is 4 on 32-bit machines and 8 on 64-bit machines.
Berkeley DB (http://www.sleepycat.com) has provided
MySQL with a transaction-safe table handler. This will survive
crashes and also provides COMMIT and ROLLBACK on
transactions. In order to build MySQL Version 3.23.x (BDB support first
appeared in Version 3.23.15) with support for BDB tables, you
will need Berkeley DB Version 3.2.3d or newer which can be downloaded from
http://www.mysql.com/downloads/mysql-3.23.html. This is a patched
version of Berkeley DB that is only available from MySQL; the
standard Berkeley DB will not work with MySQL.
If you have downloaded a binary version of MySQL that includes support for Berkeley DB, simply follow the instructions for installing a binary version of MySQL. See section 4.6 Installing a MySQL Binary Distribution.
To compile MySQL with Berkeley DB support, first uncompress the
BDB distribution into the MySQL top-level source
directory, and follow the instructions for building MySQL from
source. Configure will automatically detect and use the Berkeley
DB source you just uncompressed. See section 4.7 Installing a MySQL Source Distribution.
cd /path/to/source/of/mysql-3.23.29-gamma gzip -cd /tmp/db-3.2.3d.tar.gz | tar xf - ./configure # this will use Berkeley DB automatically
If you would like to install Berkeley DB separately, to use with
other applications and MySQL, this is possible. Follow the directions
for installing Berkeley DB in the Berkeley DB README file. Then, pass
the --with-berkeley-db=DIR option to MySQL's configure,
where DIR refers to the installation prefix used when installing
Berkeley DB (by default it is
/usr/local/BerkeleyDB.3.2). You can give additional options to
MySQL configure, --with-berkeley-db-includes=DIR and
--with-berkeley-db-libs=DIR, if the BDB includes and/or libs
directory is not under the first directory (by default they are).
Then complete the MySQL installation as normal.
Please refer to the manual provided by BDB distribution for
more/updated information.
Even though Berkeley DB is in itself very tested and reliable, the MySQL interface is still considered beta quality. We are actively improving and optimizing it to get it stable very soon.
If you are running with AUTOCOMMIT=0 then your changes in BDB
tables will not be updated until you execute COMMIT. Instead of commit
you can execute ROLLBACK to forget your changes. See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax.
If you are running with AUTOCOMMIT=1 (the default), your changes
will be committed immediately. You can start an extended transaction with
the BEGIN WORK SQL command, after which your changes will not be
committed until you execute COMMIT (or decide to ROLLBACK
the changes).
The following options to mysqld can be used to change the behavior of
BDB tables:
| Option | Meaning |
--bdb-home=directory | Base directory for BDB tables. This should be the same directory you use for --datadir. |
--bdb-lock-detect=# | Berkeley lock detect. One of (DEFAULT, OLDEST, RANDOM, or YOUNGEST). |
--bdb-logdir=directory | Berkeley DB log file directory. |
--bdb-no-sync | Don't synchronously flush logs. |
--bdb-recover | Start Berkeley DB in recover mode. |
--bdb-shared-data | Start Berkeley DB in multi-process mode (Don't use DB_PRIVATE when initializing Berkeley DB)
|
--bdb-tmpdir=directory | Berkeley DB tempfile name. |
--skip-bdb | Don't use berkeley db. |
-O bdb_max_lock=1000 | Set the maximum number of locks possible. See section 7.28.4 SHOW VARIABLES. |
If you use --skip-bdb, MySQL will not initialize the
Berkeley DB library and this will save a lot of memory. Of course,
you cannot use BDB tables if you are using this option.
Normally you should start mysqld with --bdb-recover if you intend
to use BDB tables. This may, however, give you problems when you try to
start mysqld if the BDB log files are corrupted. See section 4.16.2 Problems Starting the MySQL Server.
With bdb_max_lock you can specify the maximum number of locks
(1000 by default) you can have active on a BDB table. You should
increase this if you get errors of type bdb: Lock table is out of
available locks or Got error 12 from ... when you have do long
transactions or when mysqld has to examine a lot of rows to
calculate the query.
You may also want to change binlog_cache_size and
max_binlog_cache_size if you are using big multi-line transactions.
See section 7.31 BEGIN/COMMIT/ROLLBACK Syntax.
BDB tables:PRIMARY KEY in each BDB table to be
able to refer to previously read rows. If you don't create one,
MySQL will create an maintain a hidden PRIMARY KEY for
you. The hidden key has a length of 5 bytes and is incremented for each
insert attempt.
BDB table are part of the same index or
part of the primary key, then MySQL can execute the query
without having to access the actual row. In a MyISAM table the
above holds only if the columns are part of the same index.
PRIMARY KEY will be faster than any other key, as the
PRIMARY KEY is stored together with the row data. As the other keys are
stored as the key data + the PRIMARY KEY, it's important to keep the
PRIMARY KEY as short as possible to save disk and get better speed.
LOCK TABLES works on BDB tables as with other tables. If
you don't use LOCK TABLE, MYSQL will issue an internal
multiple-write lock on the table to ensure that the table will be
properly locked if another thread issues a table lock.
BDB tables is done on page level.
SELECT COUNT(*) FROM table_name is slow as BDB tables doesn't
maintain a count of the number of rows in the table.
MyISAM tables as one has data in BDB
tables stored in B-trees and not in a separate data file.
BDB table may make an automatic rollback and any
read may fail with a deadlock error.
BDB tables compared to MyISAM tables which don't use
PACK_KEYS=0.
FLUSH LOGS at any time
to checkpoint the Berkeley DB tables.
For disaster recovery, one should use table backups plus MySQL's binary
log. See section 21.2 Database Backups.
DELETE or ROLLBACK:s this number should be
accurate enough for the MySQL optimizer, but as MySQL
only store the number on close, it may be wrong if MySQL dies
unexpectedly. It should not be fatal even if this number is not 100 %
correct. One can update the number of rows by executing ANALYZE
TABLE or OPTIMIZE TABLE. See section 7.15 ANALYZE TABLE Syntax . See section 7.11 OPTIMIZE TABLE Syntax.
SHOW TABLE STATUS doesn't yet provide that much information for BDB
tables.
If you are running in not auto_commit mode and delete a table you
are using you may get the following error messages in the MySQL
error file:
001119 23:43:56 bdb: Missing log fileid entry 001119 23:43:56 bdb: txn_abort: Log undo failed for LSN: 1 3644744: Invalid
This is not fatal but we don't recommend that you delete tables if you are
not in auto_commit mode, until this problem is fixed (the fix is
not trivial).
This chapter provides a tutorial introduction to MySQL by showing
how to use the mysql client program to create and use a simple
database. mysql (sometimes referred to as the ``terminal monitor'' or
just ``monitor'') is an interactive program that allows you to connect to a
MySQL server, run queries, and view the results. mysql may
also be used in batch mode: you place your queries in a file beforehand, then
tell mysql to execute the contents of the file. Both ways of using
mysql are covered here.
To see a list of options provided by mysql, invoke it with
the --help option:
shell> mysql --help
This chapter assumes that mysql is installed on your machine and that
a MySQL server is available to which you can connect. If this is
not true, contact your MySQL administrator. (If you are the
administrator, you will need to consult other sections of this manual.)
This chapter describes the entire process of setting up and using a database. If you are interested only in accessing an already-existing database, you may want to skip over the sections that describe how to create the database and the tables it contains.
Because this chapter is tutorial in nature, many details are necessarily left out. Consult the relevant sections of the manual for more information on the topics covered here.
To connect to the server, you'll usually need to provide a MySQL
user name when you invoke mysql and, most likely, a password. If the
server runs on a machine other than the one where you log in, you'll also
need to specify a hostname. Contact your administrator to find out what
connection parameters you should use to connect (that is, what host, user name,
and password to use). Once you know the proper parameters, you should be
able to connect like this:
shell> mysql -h host -u user -p Enter password: ********
The ******** represents your password; enter it when mysql
displays the Enter password: prompt.
If that works, you should see some introductory information followed by a
mysql> prompt:
shell> mysql -h host -u user -p Enter password: ******** Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 459 to server version: 3.22.20a-log Type 'help' for help. mysql>
The prompt tells you that mysql is ready for you to enter commands.
Some MySQL installations allow users to connect as the anonymous
(unnamed) user to the server running on the local host. If this is the case
on your machine, you should be able to connect to that server by invoking
mysql without any options:
shell> mysql
After you have connected successfully, you can disconnect any time by typing
QUIT at the mysql> prompt:
mysql> QUIT Bye
You can also disconnect by pressing Control-D.
Most examples in the following sections assume you are connected to the
server. They indicate this by the mysql> prompt.
Make sure you are connected to the server, as discussed in the previous
section. Doing so will not in itself select any database to work with, but
that's okay. At this point, it's more important to find out a little about
how to issue queries than to jump right in creating tables, loading data
into them, and retrieving data from them. This section describes the basic
principles of entering commands, using several queries you can try out to
familiarize yourself with how mysql works.
Here's a simple command that asks the server to tell you its version number
and the current date. Type it in as shown below following the mysql>
prompt and hit the RETURN key:
mysql> SELECT VERSION(), CURRENT_DATE; +--------------+--------------+ | version() | CURRENT_DATE | +--------------+--------------+ | 3.22.20a-log | 1999-03-19 | +--------------+--------------+ 1 row in set (0.01 sec) mysql>
This query illustrates several things about mysql:
QUIT,
mentioned earlier, is one of them. We'll get to others later.)
mysql sends it to the server for execution
and displays the results, then prints another mysql> to indicate
that it is ready for another command.
mysql displays query output as a table (rows and columns). The first
row contains labels for the columns. The rows following are the query
results. Normally, column labels are the names of the columns you fetch from
database tables. If you're retrieving the value of an expression rather than
a table column (as in the example just shown), mysql labels the column
using the expression itself.
mysql shows how many rows were returned and how long the query took
to execute, which gives you a rough idea of server performance. These values
are imprecise because they represent wall clock time (not CPU or machine
time), and because they are affected by factors such as server load and
network latency. (For brevity, the ``rows in set'' line is not shown in
the remaining examples in this chapter.)
Keywords may be entered in any lettercase. The following queries are equivalent:
mysql> SELECT VERSION(), CURRENT_DATE; mysql> select version(), current_date; mysql> SeLeCt vErSiOn(), current_DATE;
Here's another query. It demonstrates that you can use mysql as a
simple calculator:
mysql> SELECT SIN(PI()/4), (4+1)*5; +-------------+---------+ | SIN(PI()/4) | (4+1)*5 | +-------------+---------+ | 0.707107 | 25 | +-------------+---------+
The commands shown thus far have been relatively short, single-line statements. You can even enter multiple statements on a single line. Just end each one with a semicolon:
mysql> SELECT VERSION(); SELECT NOW(); +--------------+ | version() | +--------------+ | 3.22.20a-log | +--------------+ +---------------------+ | NOW() | +---------------------+ | 1999-03-19 00:15:33 | +---------------------+
A command need not be given all on a single line, so lengthy commands that
require several lines are not a problem. mysql determines where your
statement ends by looking for the terminating semicolon, not by looking for
the end of the input line. (In other words, mysql
accepts free-format input: it collects input lines but does not execute them
until it sees the semicolon.)
Here's a simple multiple-line statement:
mysql> SELECT
-> USER()
-> ,
-> CURRENT_DATE;
+--------------------+--------------+
| USER() | CURRENT_DATE |
+--------------------+--------------+
| joesmith@localhost | 1999-03-18 |
+--------------------+--------------+
In this example, notice how the prompt changes from mysql> to
-> after you enter the first line of a multiple-line query. This is
how mysql indicates that it hasn't seen a complete statement and is
waiting for the rest. The prompt is your friend, because it provides
valuable feedback. If you use that feedback, you will always be aware of
what mysql is waiting for.
If you decide you don't want to execute a command that you are in the
process of entering, cancel it by typing \c:
mysql> SELECT
-> USER()
-> \c
mysql>
Here, too, notice the prompt. It switches back to mysql> after you
type \c, providing feedback to indicate that mysql is ready
for a new command.
The following table shows each of the prompts you may see and summarizes what
they mean about the state that mysql is in:
| Prompt | Meaning |
mysql> | Ready for new command. |
-> | Waiting for next line of multiple-line command. |
'> | Waiting for next line, collecting a string that begins with a single quote (`''). |
"> | Waiting for next line, collecting a string that begins with a double quote (`"'). |
Multiple-line statements commonly occur by accident when you intend to
issue a command on a single line, but forget the terminating semicolon. In
this case, mysql waits for more input:
mysql> SELECT USER()
->
If this happens to you (you think you've entered a statement but the only
response is a -> prompt), most likely mysql is waiting for the
semicolon. If you don't notice what the prompt is telling you, you might sit
there for a while before realizing what you need to do. Enter a semicolon to
complete the statement, and mysql will execute it:
mysql> SELECT USER()
-> ;
+--------------------+
| USER() |
+--------------------+
| joesmith@localhost |
+--------------------+
The '> and "> prompts occur during string collection.
In MySQL, you can write strings surrounded by either `''
or `"' characters (for example, 'hello' or "goodbye"),
and mysql lets you enter strings that span multiple lines. When you
see a '> or "> prompt, it means that you've entered a line
containing a string that begins with a `'' or `"' quote character,
but have not yet entered the matching quote that terminates the string.
That's fine if you really are entering a multiple-line string, but how likely
is that? Not very. More often, the '> and "> prompts indicate
that you've inadvertantly left out a quote character. For example:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
">
If you enter this SELECT statement, then hit RETURN and wait for the
result, nothing will happen. Instead of wondering why this
query takes so long, notice the clue provided by the "> prompt. It
tells you that mysql expects to see the rest of an unterminated
string. (Do you see the error in the statement? The string "Smith is
missing the second quote.)
At this point, what do you do? The simplest thing is to cancel the command.
However, you cannot just type \c in this case, because mysql
interprets it as part of the string that it is collecting! Instead, enter
the closing quote character (so mysql knows you've finished the
string), then type \c:
mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
"> "\c
mysql>
The prompt changes back to mysql>, indicating that mysql
is ready for a new command.
It's important to know what the '> and "> prompts signify,
because if you mistakenly enter an unterminated string, any further lines you
type will appear to be ignored by mysql -- including a line
containing QUIT! This can be quite confusing, especially if you
don't know that you need to supply the terminating quote before you can
cancel the current command.
Here are examples of how to solve some common problems with MySQL.
Some of the examples use the table shop to hold the price of each
article (item number) for certain traders (dealers). Supposing that each
trader has a single fixed price per article, then (item,
trader) is a primary key for the records.
Start the command line tool mysql and select a database:
mysql your-database-name
(In most MySQL installations, you can use the database-name 'test').
You can create the example table as:
CREATE TABLE shop ( article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL, dealer CHAR(20) DEFAULT '' NOT NULL, price DOUBLE(16,2) DEFAULT '0.00' NOT NULL, PRIMARY KEY(article, dealer)); INSERT INTO shop VALUES (1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69), (3,'D',1.25),(4,'D',19.95);
Okay, so the example data is:
SELECT * FROM shop +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0001 | A | 3.45 | | 0001 | B | 3.99 | | 0002 | A | 10.99 | | 0003 | B | 1.45 | | 0003 | C | 1.69 | | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
``What's the highest item number?''
SELECT MAX(article) AS article FROM shop +---------+ | article | +---------+ | 4 | +---------+
``Find number, dealer, and price of the most expensive article.''
In ANSI SQL this is easily done with a sub-query:
SELECT article, dealer, price FROM shop WHERE price=(SELECT MAX(price) FROM shop)
In MySQL (which does not yet have sub-selects), just do it in two steps:
SELECT statement.
SELECT article, dealer, price FROM shop WHERE price=19.95
Another solution is to sort all rows descending by price and only
get the first row using the MySQL specific LIMIT clause:
SELECT article, dealer, price FROM shop ORDER BY price DESC LIMIT 1
NOTE: If there are several most expensive articles (for example, each 19.95)
the LIMIT solution shows only one of them!
``What's the highest price per article?''
SELECT article, MAX(price) AS price FROM shop GROUP BY article +---------+-------+ | article | price | +---------+-------+ | 0001 | 3.99 | | 0002 | 10.99 | | 0003 | 1.69 | | 0004 | 19.95 | +---------+-------+
``For each article, find the dealer(s) with the most expensive price.''
In ANSI SQL, I'd do it with a sub-query like this:
SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article)
In MySQL it's best do it in several steps:
This can easily be done with a temporary table:
CREATE TEMPORARY TABLE tmp (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL);
LOCK TABLES shop read;
INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;
SELECT shop.article, dealer, price FROM shop, tmp
WHERE shop.article=tmp.article AND shop.price=tmp.price;
UNLOCK TABLES;
DROP TABLE tmp;
If you don't use a TEMPORARY table, you must also lock the 'tmp' table.
``Can it be done with a single query?''
Yes, but only by using a quite inefficient trick that I call the ``MAX-CONCAT trick'':
SELECT article,
SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
FROM shop
GROUP BY article;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | C | 1.69 |
| 0004 | D | 19.95 |
+---------+--------+-------+
The last example can, of course, be made a bit more efficient by doing the splitting of the concatenated column in the client.
You can use MySQL user variables to remember results without having to store them in a temporary variables in the client. See section 7.2 User Variables.
For example, to find the articles with the highest and lowest price you can do:
select @min_price:=min(price),@max_price:=max(price) from shop; select * from shop where price=@min_price or price=@max_price; +---------+--------+-------+ | article | dealer | price | +---------+--------+-------+ | 0003 | D | 1.25 | | 0004 | D | 19.95 | +---------+--------+-------+
You don't need foreign keys to join 2 tables.
The only thing MySQL doesn't do is CHECK to make sure that
the keys you use really exist in the table(s) you're referencing and it
doesn't automatically delete rows from table with a foreign key
definition. If you use your keys like normal, it'll work just fine:
CREATE TABLE persons (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
name CHAR(60) NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE shirts (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
style ENUM('t-shirt', 'polo', 'dress') NOT NULL,
color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL,
owner SMALLINT UNSIGNED NOT NULL REFERENCES persons,
PRIMARY KEY (id)
);
INSERT INTO persons VALUES (NULL, 'Antonio Paz');
INSERT INTO shirts VALUES
(NULL, 'polo', 'blue', LAST_INSERT_ID()),
(NULL, 'dress', 'white', LAST_INSERT_ID()),
(NULL, 't-shirt', 'blue', LAST_INSERT_ID());
INSERT INTO persons VALUES (NULL, 'Lilliana Angelovska');
INSERT INTO shirts VALUES
(NULL, 'dress', 'orange', LAST_INSERT_ID()),
(NULL, 'polo', 'red', LAST_INSERT_ID()),
(NULL, 'dress', 'blue', LAST_INSERT_ID()),
(NULL, 't-shirt', 'white', LAST_INSERT_ID());
SELECT * FROM persons;
+----+---------------------+
| id | name |
+----+---------------------+
| 1 | Antonio Paz |
| 2 | Lilliana Angelovska |
+----+---------------------+
SELECT * FROM shirts;
+----+---------+--------+-------+
| id | style | color | owner |
+----+---------+--------+-------+
| 1 | polo | blue | 1 |
| 2 | dress | white | 1 |
| 3 | t-shirt | blue | 1 |
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
| 7 | t-shirt | white | 2 |
+----+---------+--------+-------+
SELECT s.* FROM persons p, shirts s
WHERE p.name LIKE 'Lilliana%'
AND s.owner = p.id
AND s.color <> 'white';
+----+-------+--------+-------+
| id | style | color | owner |
+----+-------+--------+-------+
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
+----+-------+--------+-------+
MySQL doesn't yet optimize when you search on two different
keys combined with OR (Searching on one key with different OR
parts is optimized quite good):
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' OR field2_index = '1'
The reason is that we haven't yet had time to come up with an efficient
way to handle this in the general case. (The AND handling is,
in comparison, now completely general and works very well).
For the moment you can solve this very efficently by using a
TEMPORARY table. This type of optimization is also very good if
you are using very complicated queries where the SQL server does the
optimizations in the wrong order.
CREATE TEMPORARY TABLE tmp SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'; INSERT INTO tmp SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1'; SELECT * from tmp; DROP TABLE tmp;
The above way to solve this query is in effect an UNION of two queries.
Now that you know how to enter commands, it's time to access a database.
Suppose you have several pets in your home (your menagerie) and you'd like to keep track of various types of information about them. You can do so by creating tables to hold your data and loading them with the desired information. Then you can answer different sorts of questions about your animals by retrieving data from the tables. This section shows you how to:
The menagerie database will be simple (deliberately), but it is not difficult to think of real-world situations in which a similar type of database might be used. For example, a database like this could be used by a farmer to keep track of livestock, or by a veterinarian to keep track of patient records.
Use the SHOW statement to find out what databases currently exist
on the server:
mysql> SHOW DATABASES; +----------+ | Database | +----------+ | mysql | | test | | tmp | +----------+
The list of databases is probably different on your machine, but the
mysql and test databases are likely to be among them. The
mysql database is required because it describes user access
privileges. The test database is often provided as a workspace for
users to try things out.
If the test database exists, try to access it:
mysql> USE test Database changed
Note that USE, like QUIT, does not require a semicolon. (You
can terminate such statements with a semicolon if you like; it does no harm.)
The USE statement is special in another way, too: it must be given on
a single line.
You can use the test database (if you have access to it) for the
examples that follow, but anything you create in that database can be
removed by anyone else with access to it. For this reason, you should
probably ask your MySQL administrator for permission to use a
database of your own. Suppose you want to call yours menagerie. The
administrator needs to execute a command like this:
mysql> GRANT ALL ON menagerie.* TO your_mysql_name;
where your_mysql_name is the MySQL user name assigned to
you.
If the administrator creates your database for you when setting up your permissions, you can begin using it. Otherwise, you need to create it yourself:
mysql> CREATE DATABASE menagerie;
Under Unix, database names are case sensitive (unlike SQL keywords), so you
must always refer to your database as menagerie, not as
Menagerie, MENAGERIE, or some other variant. This is also true
for table names. (Under Windows, this restriction does not apply, although
you must refer to databases and tables using the same lettercase throughout a
given query.)
Creating a database does not select it for use; you must do that explicitly.
To make menagerie the current database, use this command:
mysql> USE menagerie Database changed
Your database needs to be created only once, but you must select it for use
each time you begin a mysql session. You can do this by issuing a
USE statement as shown above. Alternatively, you can select the
database on the command line when you invoke mysql. Just specify its
name after any connection parameters that you might need to provide. For
example:
shell> mysql -h host -u user -p menagerie Enter password: ********
Note that menagerie is not your password on the command just shown.
If you want to supply your password on the command line after the -p
option, you must do so with no intervening space (for example, as
-pmypassword, not as -p mypassword). However, putting your
password on the command line is not recommended, because doing so exposes it
to snooping by other users logged in on your machine.
Creating the database is the easy part, but at this point it's empty, as
SHOW TABLES will tell you:
mysql> SHOW TABLES; Empty set (0.00 sec)
The harder part is deciding what the structure of your database should be: what tables you will need and what columns will be in each of them.
You'll want a table that contains a record for each of your pets. This can
be called the pet table, and it should contain, as a bare minimum,
each animal's name. Because the name by itself is not very interesting, the
table should contain other information. For example, if more than one person
in your family keeps pets, you might want to list each animal's owner. You
might also want to record some basic descriptive information such as species
and sex.
How about age? That might be of interest, but it's not a good thing to store in a database. Age changes as time passes, which means you'd have to update your records often. Instead, it's better to store a fixed value such as date of birth. Then, whenever you need age, you can calculate it as the difference between the current date and the birth date. MySQL provides functions for doing date arithmetic, so this is not difficult. Storing birth date rather than age has other advantages, too:
You can probably think of other types of information that would be useful in
the pet table, but the ones identified so far are sufficient for now:
name, owner, species, sex, birth, and death.
Use a CREATE TABLE statement to specify the layout of your table:
mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
-> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);
VARCHAR is a good choice for the name, owner, and
species columns because the column values will vary in length. The
lengths of those columns need not all be the same, and need not be
20. You can pick any length from 1 to 255, whatever
seems most reasonable to you. (If you make a poor choice and it turns
out later that you need a longer field, MySQL provides an
ALTER TABLE statement.)
Animal sex can be represented in a variety of ways, for example, "m"
and "f", or perhaps "male" and "female". It's simplest
to use the single characters "m" and "f".
The use of the DATE data type for the birth and death
columns is a fairly obvious choice.
Now that you have created a table, SHOW TABLES should produce some
output:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | pet | +---------------------+
To verify that your table was created the way you expected, use
a DESCRIBE statement:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
You can use DESCRIBE any time, for example, if you forget the names of
the columns in your table or what types they are.
After creating your table, you need to populate it. The LOAD DATA and
INSERT statements are useful for this.
Suppose your pet records can be described as shown below.
(Observe that MySQL expects dates in YYYY-MM-DD format;
this may be different than what you are used to.)
| name | owner | species | sex | birth | death |
| Fluffy | Harold | cat | f | 1993-02-04 | |
| Claws | Gwen | cat | m | 1994-03-17 | |
| Buffy | Harold | dog | f | 1989-05-13 | |
| Fang | Benny | dog | m | 1990-08-27 | |
| Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 |
| Chirpy | Gwen | bird | f | 1998-09-11 | |
| Whistler | Gwen | bird | 1997-12-09 | ||
| Slim | Benny | snake | m | 1996-04-29 |
Because you are beginning with an empty table, an easy way to populate it is to create a text file containing a row for each of your animals, then load the contents of the file into the table with a single statement.
You could create a text file `pet.txt' containing one record per line,
with values separated by tabs, and given in the order in which the columns
were listed in the CREATE TABLE statement. For missing values (such
as unknown sexes or death dates for animals that are still living), you can
use NULL values. To represent these in your text file, use
\N. For example, the record for Whistler the bird would look like
this (where the whitespace between values is a single tab character):
Whistler | Gwen | bird | \N | 1997-12-09 | \N
|
To load the text file `pet.txt' into the pet table, use this
command:
mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;
You can specify the column value separator and end of line marker explicitly
in the LOAD DATA statement if you wish, but the defaults are tab and
linefeed. These are sufficient for the statement to read the file
`pet.txt' properly.
When you want to add new records one at a time, the INSERT statement
is useful. In its simplest form, you supply values for each column, in the
order in which the columns were listed in the CREATE TABLE statement.
Suppose Diane gets a new hamster named Puffball. You could add a new record
using an INSERT statement like this:
mysql> INSERT INTO pet
-> VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);
Note that string and date values are specified as quoted strings here. Also,
with INSERT, you can insert NULL directly to represent a
missing value. You do not use \N like you do with LOAD DATA.
From this example, you should be able to see that there would be a lot more
typing involved to load
your records initially using several INSERT statements rather
than a single LOAD DATA statement.
The SELECT statement is used to pull information from a table.
The general form of the statement is:
SELECT what_to_select FROM which_table WHERE conditions_to_satisfy
what_to_select indicates what you want to see. This can be a list of
columns, or * to indicate ``all columns.'' which_table
indicates the table from which you want to retrieve data. The WHERE
clause is optional. If it's present, conditions_to_satisfy specifies
conditions that rows must satisfy to qualify for retrieval.
The simplest form of SELECT retrieves everything from a table:
mysql> SELECT * FROM pet; +----------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+--------+---------+------+------------+------------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Fang | Benny | dog | m | 1990-08-27 | NULL | | Bowser | Diane | dog | m | 1998-08-31 | 1995-07-29 | | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+--------+---------+------+------------+------------+
This form of SELECT is useful if you want to review your entire table,
for instance, after you've just loaded it with your initial dataset. As it
happens, the output just shown reveals an error in your data file: Bowser
appears to have been born after he died! Consulting your original pedigree
papers, you find that the correct birth year is 1989, not 1998.
There are are least a couple of ways to fix this:
DELETE and LOAD DATA:
mysql> SET AUTOCOMMIT=1; # Used for quick re-create of the table mysql> DELETE FROM pet; mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;However, if you do this, you must also re-enter the record for Puffball.
UPDATE statement:
mysql> UPDATE pet SET birth = "1989-08-31" WHERE name = "Bowser";
As shown above, it is easy to retrieve an entire table. But typically you don't want to do that, particularly when the table becomes large. Instead, you're usually more interested in answering a particular question, in which case you specify some constraints on the information you want. Let's look at some selection queries in terms of questions about your pets that they answer.
You can select only particular rows from your table. For example, if you want to verify the change that you made to Bowser's birth date, select Bowser's record like this:
mysql> SELECT * FROM pet WHERE name = "Bowser"; +--------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+-------+---------+------+------------+------------+ | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+-------+---------+------+------------+------------+
The output confirms that the year is correctly recorded now as 1989, not 1998.
String comparisons are normally case insensitive, so you can specify the
name as "bowser", "BOWSER", etc. The query result will be
the same.
You can specify conditions on any column, not just name. For example,
if you want to know which animals were born after 1998, test the birth
column:
mysql> SELECT * FROM pet WHERE birth >= "1998-1-1"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Puffball | Diane | hamster | f | 1999-03-30 | NULL | +----------+-------+---------+------+------------+-------+
You can combine conditions, for example, to locate female dogs:
mysql> SELECT * FROM pet WHERE species = "dog" AND sex = "f"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The preceding query uses the AND logical operator. There is also an
OR operator:
mysql> SELECT * FROM pet WHERE species = "snake" OR species = "bird"; +----------+-------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+-------+ | Chirpy | Gwen | bird | f | 1998-09-11 | NULL | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | | Slim | Benny | snake | m | 1996-04-29 | NULL | +----------+-------+---------+------+------------+-------+
AND and OR may be intermixed. If you do that, it's a good idea
to use parentheses to indicate how conditions should be grouped:
mysql> SELECT * FROM pet WHERE (species = "cat" AND sex = "m")
-> OR (species = "dog" AND sex = "f");
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
If you don't want to see entire rows from your table, just name the columns
in which you're interested, separated by commas. For example, if you want to
know when your animals were born, select the name and birth
columns:
mysql> SELECT name, birth FROM pet; +----------+------------+ | name | birth | +----------+------------+ | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Buffy | 1989-05-13 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Puffball | 1999-03-30 | +----------+------------+
To find out who owns pets, use this query:
mysql> SELECT owner FROM pet; +--------+ | owner | +--------+ | Harold | | Gwen | | Harold | | Benny | | Diane | | Gwen | | Gwen | | Benny | | Diane | +--------+
However, notice that the query simply retrieves the owner field from
each record, and some of them appear more than once. To minimize the output,
retrieve each unique output record just once by adding the keyword
DISTINCT:
mysql> SELECT DISTINCT owner FROM pet; +--------+ | owner | +--------+ | Benny | | Diane | | Gwen | | Harold | +--------+
You can use a WHERE clause to combine row selection with column
selection. For example, to get birth dates for dogs and cats only,
use this query:
mysql> SELECT name, species, birth FROM pet
-> WHERE species = "dog" OR species = "cat";
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
| Fang | dog | 1990-08-27 |
| Bowser | dog | 1989-08-31 |
+--------+---------+------------+
You may have noticed in the preceding examples that the result rows are
displayed in no particular order. However, it's often easier to examine
query output when the rows are sorted in some meaningful way. To sort a
result, use an ORDER BY clause.
Here are animal birthdays, sorted by date:
mysql> SELECT name, birth FROM pet ORDER BY birth; +----------+------------+ | name | birth | +----------+------------+ | Buffy | 1989-05-13 | | Bowser | 1989-08-31 | | Fang | 1990-08-27 | | Fluffy | 1993-02-04 | | Claws | 1994-03-17 | | Slim | 1996-04-29 | | Whistler | 1997-12-09 | | Chirpy | 1998-09-11 | | Puffball | 1999-03-30 | +----------+------------+
To sort in reverse order, add the DESC (descending) keyword to the
name of the column you are sorting by:
mysql> SELECT name, birth FROM pet ORDER BY birth DESC; +----------+------------+ | name | birth | +----------+------------+ | Puffball | 1999-03-30 | | Chirpy | 1998-09-11 | | Whistler | 1997-12-09 | | Slim | 1996-04-29 | | Claws | 1994-03-17 | | Fluffy | 1993-02-04 | | Fang | 1990-08-27 | | Bowser | 1989-08-31 | | Buffy | 1989-05-13 | +----------+------------+
You can sort on multiple columns. For example, to sort by type of animal, then by birth date within animal type with youngest animals first, use the following query:
mysql> SELECT name, species, birth FROM pet ORDER BY species, birth DESC; +----------+---------+------------+ | name | species | birth | +----------+---------+------------+ | Chirpy | bird | 1998-09-11 | | Whistler | bird | 1997-12-09 | | Claws | cat | 1994-03-17 | | Fluffy | cat | 1993-02-04 | | Fang | dog | 1990-08-27 | | Bowser | dog | 1989-08-31 | | Buffy | dog | 1989-05-13 | | Puffball | hamster | 1999-03-30 | | Slim | snake | 1996-04-29 | +----------+---------+------------+
Note that the DESC keyword applies only to the column name immediately
preceding it (birth); species values are still sorted in
ascending order.
MySQL provides several functions that you can use to perform calculations on dates, for example, to calculate ages or extract parts of dates.
To determine how many years old each of your pets is, compute age as the difference between the birth date and the current date. Do this by converting the two dates to days, take the difference, and divide by 365 (the number of days in a year):
mysql> SELECT name, (TO_DAYS(NOW())-TO_DAYS(birth))/365 FROM pet; +----------+-------------------------------------+ | name | (TO_DAYS(NOW())-TO_DAYS(birth))/365 | +----------+-------------------------------------+ | Fluffy | 6.15 | | Claws | 5.04 | | Buffy | 9.88 | | Fang | 8.59 | | Bowser | 9.58 | | Chirpy | 0.55 | | Whistler | 1.30 | | Slim | 2.92 | | Puffball | 0.00 | +----------+-------------------------------------+
Although the query works, there are some things about it that could be improved. First, the result could be scanned more easily if the rows were presented in some order. Second, the heading for the age column isn't very meaningful.
The first problem can be handled by adding an ORDER BY name clause to
sort the output by name. To deal with the column heading, provide a name for
the column so that a different label appears in the output (this is called a
column alias):
mysql> SELECT name, (TO_DAYS(NOW())-TO_DAYS(birth))/365 AS age
-> FROM pet ORDER BY name;
+----------+------+
| name | age |
+----------+------+
| Bowser | 9.58 |
| Buffy | 9.88 |
| Chirpy | 0.55 |
| Claws | 5.04 |
| Fang | 8.59 |
| Fluffy | 6.15 |
| Puffball | 0.00 |
| Slim | 2.92 |
| Whistler | 1.30 |
+----------+------+
To sort the output by age rather than name, just use a
different ORDER BY clause:
mysql> SELECT name, (TO_DAYS(NOW())-TO_DAYS(birth))/365 AS age
-> FROM pet ORDER BY age;
+----------+------+
| name | age |
+----------+------+
| Puffball | 0.00 |
| Chirpy | 0.55 |
| Whistler | 1.30 |
| Slim | 2.92 |
| Claws | 5.04 |
| Fluffy | 6.15 |
| Fang | 8.59 |
| Bowser | 9.58 |
| Buffy | 9.88 |
+----------+------+
A similar query can be used to determine age at death for animals that have
died. You determine which animals these are by checking whether or not the
death value is NULL. Then, for those with non-NULL
values, compute the difference between the death and birth
values:
mysql> SELECT name, birth, death, (TO_DAYS(death)-TO_DAYS(birth))/365 AS age
-> FROM pet WHERE death IS NOT NULL ORDER BY age;
+--------+------------+------------+------+
| name | birth | death | age |
+--------+------------+------------+------+
| Bowser | 1989-08-31 | 1995-07-29 | 5.91 |
+--------+------------+------------+------+
The query uses death IS NOT NULL rather than death != NULL
because NULL is a special value. This is explained later.
See section 9.5.4.6 Working with NULL Values.
What if you want to know which animals have birthdays next month? For this
type of calculation, year and day are irrelevant; you simply want to extract
the month part of the birth column. MySQL provides several
date-part extraction functions, such as YEAR(), MONTH(), and
DAYOFMONTH(). MONTH() is the appropriate function here. To
see how it works, run a simple query that displays the value of both
birth and MONTH(birth):
mysql> SELECT name, birth, MONTH(birth) FROM pet; +----------+------------+--------------+ | name | birth | MONTH(birth) | +----------+------------+--------------+ | Fluffy | 1993-02-04 | 2 | | Claws | 1994-03-17 | 3 | | Buffy | 1989-05-13 | 5 | | Fang | 1990-08-27 | 8 | | Bowser | 1989-08-31 | 8 | | Chirpy | 1998-09-11 | 9 | | Whistler | 1997-12-09 | 12 | | Slim | 1996-04-29 | 4 | | Puffball | 1999-03-30 | 3 | +----------+------------+--------------+
Finding animals with birthdays in the upcoming month is easy, too. Suppose
the current month is April. Then the month value is 4 and you look
for animals born in May (month 5) like this:
mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5; +-------+------------+ | name | birth | +-------+------------+ | Buffy | 1989-05-13 | +-------+------------+
There is a small complication if the current month is December, of course.
You don't just add one to the month number (12) and look for animals
born in month 13, because there is no such month. Instead, you look for
animals born in January (month 1).
You can even write the query so that it works no matter what the current
month is. That way you don't have to use a particular month number
in the query. DATE_ADD() allows you to add a time interval to a
given date. If you add a month to the value of NOW(), then extract
the month part with MONTH(), the result produces the month in which to
look for birthdays:
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MONTH(DATE_ADD(NOW(), INTERVAL 1 MONTH));
A different way to accomplish the same task is to add 1 to get the
next month after the current one (after using the modulo function (MOD)
to wrap around the month value to 0 if it is currently
12):
mysql> SELECT name, birth FROM pet
-> WHERE MONTH(birth) = MOD(MONTH(NOW()), 12) + 1;
Note that MONTH returns a number between 1 and 12. And
MOD(something,12) returns a number between 0 and 11. So the
addition has to be after the MOD() otherwise we would go from
November (11) to January (1).
NULL Values
The NULL value can be surprising until you get used to it.
Conceptually, NULL means missing value or unknown value and it
is treated somewhat differently than other values. To test for NULL,
you cannot use the arithmetic comparison operators such as =, <,
or !=. To demonstrate this for yourself, try the following query:
mysql> SELECT 1 = NULL, 1 != NULL, 1 < NULL, 1 > NULL; +----------+-----------+----------+----------+ | 1 = NULL | 1 != NULL | 1 < NULL | 1 > NULL | +----------+-----------+----------+----------+ | NULL | NULL | NULL | NULL | +----------+-----------+----------+----------+
Clearly you get no meaningful results from these comparisons. Use
the IS NULL and IS NOT NULL operators instead:
mysql> SELECT 1 IS NULL, 1 IS NOT NULL; +-----------+---------------+ | 1 IS NULL | 1 IS NOT NULL | +-----------+---------------+ | 0 | 1 | +-----------+---------------+
In MySQL, 0 means false and 1 means true.
This special treatment of NULL is why, in the previous section, it
was necessary to determine which animals are no longer alive using
death IS NOT NULL instead of death != NULL.
MySQL provides standard SQL pattern matching as well as a form of
pattern matching based on extended regular expressions similar to those used
by Unix utilities such as vi, grep, and sed.
SQL pattern matching allows you to use `_' to match any single
character and `%' to match an arbitrary number of characters (including
zero characters). In MySQL, SQL patterns are case insensitive by
default. Some examples are shown below. Note that you do not use =
or != when you use SQL patterns; use the LIKE or NOT
LIKE comparison operators instead.
To find names beginning with `b':
mysql> SELECT * FROM pet WHERE name LIKE "b%"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
To find names ending with `fy':
mysql> SELECT * FROM pet WHERE name LIKE "%fy"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a `w':
mysql> SELECT * FROM pet WHERE name LIKE "%w%"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
To find names containing exactly five characters, use the `_' pattern character:
mysql> SELECT * FROM pet WHERE name LIKE "_____"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
The other type of pattern matching provided by MySQL uses extended
regular expressions. When you test for a match for this type of pattern, use
the REGEXP and NOT REGEXP operators (or RLIKE and
NOT RLIKE, which are synonyms).
Some characteristics of extended regular expressions are:
To demonstrate how extended regular expressions work, the LIKE queries
shown above are rewritten below to use REGEXP.
To find names beginning with `b', use `^' to match the beginning of the name and `[bB]' to match either lowercase or uppercase `b':
mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+
To find names ending with `fy', use `$' to match the end of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "fy$"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+
To find names containing a `w', use `[wW]' to match either lowercase or uppercase `w':
mysql> SELECT * FROM pet WHERE name REGEXP "[wW]"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+
Because a regular expression pattern matches if it occurs anywhere in the value, it is not necessary in the previous query to put a wild card on either side of the pattern to get it to match the entire value like it would be if you used a SQL pattern.
To find names containing exactly five characters, use `^' and `$' to match the beginning and end of the name, and five instances of `.' in between:
mysql> SELECT * FROM pet WHERE name REGEXP "^.....$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+
You could also write the previous query using the `{n}'
``repeat-n-times'' operator:
mysql> SELECT * FROM pet WHERE name REGEXP "^.{5}$";
+-------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
Databases are often used to answer the question, ``How often does a certain type of data occur in a table?'' For example, you might want to know how many pets you have, or how many pets each owner has, or you might want to perform various kinds of censuses on your animals.
Counting the total number of animals you have is the same question as ``How
many rows are in the pet table?'' because there is one record per pet.
The COUNT() function counts the number of non-NULL results, so
the query to count your animals looks like this:
mysql> SELECT COUNT(*) FROM pet; +----------+ | COUNT(*) | +----------+ | 9 | +----------+
Earlier, you retrieved the names of the people who owned pets. You can
use COUNT() if you want to find out how many pets each owner has:
mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner; +--------+----------+ | owner | COUNT(*) | +--------+----------+ | Benny | 2 | | Diane | 2 | | Gwen | 3 | | Harold | 2 | +--------+----------+
Note the use of GROUP BY to group together all records for each
owner. Without it, all you get is an error message:
mysql> SELECT owner, COUNT(owner) FROM pet; ERROR 1140 at line 1: Mixing of GROUP columns (MIN(),MAX(),COUNT()...) with no GROUP columns is illegal if there is no GROUP BY clause
COUNT() and GROUP BY are useful for characterizing your
data in various ways. The following examples show different ways to
perform animal census operations.
Number of animals per species:
mysql> SELECT species, COUNT(*) FROM pet GROUP BY species; +---------+----------+ | species | COUNT(*) | +---------+----------+ | bird | 2 | | cat | 2 | | dog | 3 | | hamster | 1 | | snake | 1 | +---------+----------+
Number of animals per sex:
mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex; +------+----------+ | sex | COUNT(*) | +------+----------+ | NULL | 1 | | f | 4 | | m | 4 | +------+----------+
(In this output, NULL indicates sex unknown.)
Number of animals per combination of species and sex:
mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex; +---------+------+----------+ | species | sex | COUNT(*) | +---------+------+----------+ | bird | NULL | 1 | | bird | f | 1 | | cat | f | 1 | | cat | m | 1 | | dog | f | 1 | | dog | m | 2 | | hamster | f | 1 | | snake | m | 1 | +---------+------+----------+
You need not retrieve an entire table when you use COUNT(). For
example, the previous query, when performed just on dogs and cats, looks like
this:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE species = "dog" OR species = "cat"
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
+---------+------+----------+
Or, if you wanted the number of animals per sex only for known-sex animals:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE sex IS NOT NULL
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| bird | f | 1 |
| cat | f | 1 |
| cat | m | 1 |
| dog | f | 1 |
| dog | m | 2 |
| hamster | f | 1 |
| snake | m | 1 |
+---------+------+----------+
The pet table keeps track of which pets you have. If you want to
record other information about them, such as events in their lives like
visits to the vet or when litters are born, you need another table. What
should this table look like? It needs:
Given these considerations, the CREATE TABLE statement for the
event table might look like this:
mysql> CREATE TABLE event (name VARCHAR(20), date DATE,
-> type VARCHAR(15), remark VARCHAR(255));
As with the pet table, it's easiest to load the initial records
by creating a tab-delimited text file containing the information:
| Fluffy | 1995-05-15 | litter | 4 kittens, 3 female, 1 male |
| Buffy | 1993-06-23 | litter | 5 puppies, 2 female, 3 male |
| Buffy | 1994-06-19 | litter | 3 puppies, 3 female |
| Chirpy | 1999-03-21 | vet | needed beak straightened |
| Slim | 1997-08-03 | vet | broken rib |
| Bowser | 1991-10-12 | kennel | |
| Fang | 1991-10-12 | kennel | |
| Fang | 1998-08-28 | birthday | Gave him a new chew toy |
| Claws | 1998-03-17 | birthday | Gave him a new flea collar |
| Whistler | 1998-12-09 | birthday | First birthday |
Load the records like this:
mysql> LOAD DATA LOCAL INFILE "event.txt" INTO TABLE event;
Based on what you've learned from the queries you've run on the pet
table, you should be able to perform retrievals on the records in the
event table; the principles are the same. But when is the
event table by itself insufficient to answer questions you might ask?
Suppose you want to find out the ages of each pet when they had their
litters. The event table indicates when this occurred, but to
calculate the age of the mother, you need her birth date. Because that is
stored in the pet table, you need both tables for the query:
mysql> SELECT pet.name, (TO_DAYS(date) - TO_DAYS(birth))/365 AS age, remark
-> FROM pet, event
-> WHERE pet.name = event.name AND type = "litter";
+--------+------+-----------------------------+
| name | age | remark |
+--------+------+-----------------------------+
| Fluffy | 2.27 | 4 kittens, 3 female, 1 male |
| Buffy | 4.12 | 5 puppies, 2 female, 3 male |
| Buffy | 5.10 | 3 puppies, 3 female |
+--------+------+-----------------------------+
There are several things to note about this query:
FROM clause lists two tables because the query needs to pull
information from both of them.
name column. The query uses
WHERE clause to match up records in the two tables based on the
name values.
name column occurs in both tables, you must be specific
about which table you mean when referring to the column. This is done
by prepending the table name to the column name.
You need not have two different tables to perform a join. Sometimes it is
useful to join a table to itself, if you want to compare records in a table
to other records in that same table. For example, to find breeding pairs
among your pets, you can join the pet table with itself to pair up
males and females of like species:
mysql> SELECT p1.name, p1.sex, p2.name, p2.sex, p1.species
-> FROM pet AS p1, pet AS p2
-> WHERE p1.species = p2.species AND p1.sex = "f" AND p2.sex = "m";
+--------+------+--------+------+---------+
| name | sex | name | sex | species |
+--------+------+--------+------+---------+
| Fluffy | f | Claws | m | cat |
| Buffy | f | Fang | m | dog |
| Buffy | f | Bowser | m | dog |
+--------+------+--------+------+---------+
In this query, we specify aliases for the table name in order to refer to the columns and keep straight which instance of the table each column reference is associated with.
What if you forget the name of a database or table, or what the structure of a given table is (for example, what its columns are called)? MySQL addresses this problem through several statements that provide information about the databases and tables it supports.
You have already seen SHOW DATABASES, which lists the databases
managed by the server. To find out which database is currently selected,
use the DATABASE() function:
mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | menagerie | +------------+
If you haven't selected any database yet, the result is blank.
To find out what tables the current database contains (for example, when you're not sure about the name of a table), use this command:
mysql> SHOW TABLES; +---------------------+ | Tables in menagerie | +---------------------+ | event | | pet | +---------------------+
If you want to find out about the structure of a table, the DESCRIBE
command is useful; it displays information about each of a table's columns:
mysql> DESCRIBE pet; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | name | varchar(20) | YES | | NULL | | | owner | varchar(20) | YES | | NULL | | | species | varchar(20) | YES | | NULL | | | sex | char(1) | YES | | NULL | | | birth | date | YES | | NULL | | | death | date | YES | | NULL | | +---------+-------------+------+-----+---------+-------+
Field indicates the column name, Type is the data type for
the column, Null indicates whether or not the column can contain
NULL values, Key indicates whether or not the column is
indexed, and Default specifies the column's default value.
If you have indexes on a table,
SHOW INDEX FROM tbl_name produces information about them.
mysql in Batch Mode
In the previous sections, you used mysql interactively to enter
queries and view the results. You can also run mysql in batch
mode. To do this, put the commands you want to run in a file, then
tell mysql to read its input from the file:
shell> mysql < batch-file
If you need to specify connection parameters on the command line, the command might look like this:
shell> mysql -h host -u user -p < batch-file Enter password: ********
When you use mysql this way, you are creating a script file, then
executing the script.
Why use a script? Here are a few reasons:
mysql to execute it again.
shell> mysql < batch-file | more
shell> mysql < batch-file > mysql.out
cron job. In this case, you must use batch mode.
The default output format is different (more concise) when you run
mysql in batch mode than when you use it interactively. For
example, the output of SELECT DISTINCT species FROM pet looks like
this when run interactively:
+---------+ | species | +---------+ | bird | | cat | | dog | | hamster | | snake | +---------+
But like this when run in batch mode:
species bird cat dog hamster snake
If you want to get the interactive output format in batch mode, use
mysql -t. To echo to the output the commands that are executed, use
mysql -vvv.
At Analytikerna and Lentus, we have been doing the systems and field work for a big research project. This project is a collaboration between the Institute of Environmental Medicine at Karolinska Institutet Stockholm and the Section on Clinical Research in Aging and Psychology at the University of Southern California.
The project involves a screening part where all twins in Sweden older than 65 years are interviewed by telephone. Twins who meet certain criteria are passed on to the next stage. In this latter stage, twins who want to participate are visited by a doctor/nurse team. Some of the examinations include physical and neuropsychological examination, laboratory testing, neuroimaging, psychological status assessment, and family history collection. In addition, data are collected on medical and environmental risk factors.
More information about Twin studies can be found at:
http://www.imm.ki.se/TWIN/TWINUKW.HTM
The latter part of the project is administered with a Web interface written using Perl and MySQL.
Each night all data from the interviews are moved into a MySQL database.
The following query is used to determine who goes into the second part of the project:
select
concat(p1.id, p1.tvab) + 0 as tvid,
concat(p1.christian_name, " ", p1.surname) as Name,
p1.postal_code as Code,
p1.city as City,
pg.abrev as Area,
if(td.participation = "Aborted", "A", " ") as A,
p1.dead as dead1,
l.event as event1,
td.suspect as tsuspect1,
id.suspect as isuspect1,
td.severe as tsevere1,
id.severe as isevere1,
p2.dead as dead2,
l2.event as event2,
h2.nurse as nurse2,
h2.doctor as doctor2,
td2.suspect as tsuspect2,
id2.suspect as isuspect2,
td2.severe as tsevere2,
id2.severe as isevere2,
l.finish_date
from
twin_project as tp
/* For Twin 1 */
left join twin_data as td on tp.id = td.id and tp.tvab = td.tvab
left join informant_data as id on tp.id = id.id and tp.tvab = id.tvab
left join harmony as h on tp.id = h.id and tp.tvab = h.tvab
left join lentus as l on tp.id = l.id and tp.tvab = l.tvab
/* For Twin 2 */
left join twin_data as td2 on p2.id = td2.id and p2.tvab = td2.tvab
left join informant_data as id2 on p2.id = id2.id and p2.tvab = id2.tvab
left join harmony as h2 on p2.id = h2.id and p2.tvab = h2.tvab
left join lentus as l2 on p2.id = l2.id and p2.tvab = l2.tvab,
person_data as p1,
person_data as p2,
postal_groups as pg
where
/* p1 gets main twin and p2 gets his/her twin. */
/* ptvab is a field inverted from tvab */
p1.id = tp.id and p1.tvab = tp.tvab and
p2.id = p1.id and p2.ptvab = p1.tvab and
/* Just the sceening survey */
tp.survey_no = 5 and
/* Skip if partner died before 65 but allow emigration (dead=9) */
(p2.dead = 0 or p2.dead = 9 or
(p2.dead = 1 and
(p2.death_date = 0 or
(((to_days(p2.death_date) - to_days(p2.birthday)) / 365)
>= 65))))
and
(
/* Twin is suspect */
(td.future_contact = 'Yes' and td.suspect = 2) or
/* Twin is suspect - Informant is Blessed */
(td.future_contact = 'Yes' and td.suspect = 1 and id.suspect = 1) or
/* No twin - Informant is Blessed */
(ISNULL(td.suspect) and id.suspect = 1 and id.future_contact = 'Yes') or
/* Twin broken off - Informant is Blessed */
(td.participation = 'Aborted'
and id.suspect = 1 and id.future_contact = 'Yes') or
/* Twin broken off - No inform - Have partner */
(td.participation = 'Aborted' and ISNULL(id.suspect) and p2.dead = 0))
and
l.event = 'Finished'
/* Get at area code */
and substring(p1.postal_code, 1, 2) = pg.code
/* Not already distributed */
and (h.nurse is NULL or h.nurse=00 or h.doctor=00)
/* Has not refused or been aborted */
and not (h.status = 'Refused' or h.status = 'Aborted'
or h.status = 'Died' or h.status = 'Other')
order by
tvid;
Some explanations:
concat(p1.id, p1.tvab) + 0 as tvid
id and tvab in
numerical order. Adding 0 to the result causes MySQL to
treat the result as a number.
id
tvab
1 or 2.
ptvab
tvab. When tvab is 1 this is
2, and vice versa. It exists to save typing and to make it easier for
MySQL to optimize the query.
This query demonstrates, among other things, how to do lookups on a
table from the same table with a join (p1 and p2). In the example, this
is used to check whether a twin's partner died before the age of 65. If so,
the row is not returned.
All of the above exist in all tables with twin-related information. We
have a key on both id,tvab (all tables), and id,ptvab
(person_data) to make queries faster.
On our production machine (A 200MHz UltraSPARC), this query returns about 150-200 rows and takes less than one second.
The current number of records in the tables used above:
| Table | Rows |
person_data | 71074 |
lentus | 5291 |
twin_project | 5286 |
twin_data | 2012 |
informant_data | 663 |
harmony | 381 |
postal_groups | 100 |
Each interview ends with a status code called event. The query
shown below is used to display a table over all twin pairs combined by
event. This indicates in how many pairs both twins are finished, in how many
pairs one twin is finished and the other refused, and so on.
select
t1.event,
t2.event,
count(*)
from
lentus as t1,
lentus as t2,
twin_project as tp
where
/* We are looking at one pair at a time */
t1.id = tp.id
and t1.tvab=tp.tvab
and t1.id = t2.id
/* Just the sceening survey */
and tp.survey_no = 5
/* This makes each pair only appear once */
and t1.tvab='1' and t2.tvab='2'
group by
t1.event, t2.event;
mysqld can issue error messages in the following languages:
Czech, Danish, Dutch, English (the default), Estonian, French, German, Greek,
Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish,
Portuguese, Romanian, Russian, Slovak, Spanish, and Swedish.
To start mysqld with a particular language, use either the
--language=lang or -L lang options. For example:
shell> mysqld --language=swedish
or:
shell> mysqld --language=/usr/local/share/swedish
Note that all language names are specified in lowercase.
The language files are located (by default) in `mysql_base_dir/share/LANGUAGE/'.
To update the error message file, you should edit the `errmsg.txt' file and execute the following command to generate the `errmsg.sys' file:
shell> comp_err errmsg.txt errmsg.sys
If you upgrade to a newer version of MySQL, remember to repeat your changes with the new `errmsg.txt' file.
By default, MySQL uses the ISO-8859-1 (Latin1) character set. This is the character set used in the USA and western Europe.
The character set determines what characters are allowed in names and how
things are sorted by the ORDER BY and GROUP BY clauses of
the SELECT statement.
You can change the character set with the
--default-character-set option when you start the server.
The character sets available depend on the --with-charset=charset
option to configure, and the character set configuration files
listed in `SHAREDIR/charsets/Index'.
See section 4.7.1 Quick Installation Overview.
When a client connects to a MySQL server, the server sends the default character set in use to the client. The client will switch to use this character set for this connection.
One should use mysql_real_escape_string() when escaping strings
for a SQL query. mysql_real_escape_string() is identical to the
old mysql_escape_string() function, except that it takes the MYSQL
connection handle as the first parameter.
If the client is compiled with different paths than where the server is installed and the user who configured MySQL didn't included all character sets in the MySQL binary, one must specify for the client where it can find the additional character sets it will need if the server runs with a different character set than the client.
One can specify this by putting in a MySQL option file:
[client] default-set-dir=/usr/local/mysql/share/mysql/charsets
where the path points to where the dynamic MySQL character sets are stored.
One can force the client to use specific character set by specifying:
[client] default-character-set=character-set-name
but normally this is never needed.
To add another character set to MySQL, use the following procedure.
MYSET below.
CHARSETS_AVAILABLE and
COMPILED_CHARSETS lists in configure.in.
MYNUMBER below.
ctype_MYSET, to_lower_MYSET, and so on.
Near the top of the file, place a special comment like this:
/* * This comment is parsed by configure to create ctype.c, * so don't change it unless you know what you are doing. * * .configure. number_MYSET=MYNUMBER * .configure. strxfrm_multiply_MYSET=N * .configure. mbmaxlen_MYSET=N */The
configure program uses this comment to include
the character set into the MySQL library automatically.
The strxfrm_multiply and mbmaxlen lines will be explained in
the following sections. Only include them if you the string
collating functions or the multi-byte character set functions,
respectively.
to_lower[] and to_upper[] are simple arrays that hold the
lowercase and uppercase characters corresponding to each member of the
character set. For example:
to_lower['A'] should contain 'a' to_upper['a'] should contain 'A'
sort_order[] is a map indicating how characters should be ordered for
comparison and sorting purposes. For many character sets, this is the same as
to_upper[] (which means sorting will be case insensitive).
MySQL will sort characters based on the value of
sort_order[character]. For more complicated sorting rules, see
the discussion of string collating below.
ctype[] is an array of bit values, with one element for one character.
(Note that to_lower[], to_upper[], and sort_order[]
are indexed by character value, but ctype[] is indexed by character
value + 1. This is an old legacy to be able to handle EOF.)
You can find the following bitmask definitions in `m_ctype.h':
#define _U 01 /* Uppercase */ #define _L 02 /* Lowercase */ #define _N 04 /* Numeral (digit) */ #define _S 010 /* Spacing character */ #define _P 020 /* Punctuation */ #define _C 040 /* Control character */ #define _B 0100 /* Blank */ #define _X 0200 /* heXadecimal digit */The
ctype[] entry for each character should be the union of the
applicable bitmask values that describe the character.
For example, 'A' is an uppercase character (_U) as well as a
hexadecimal digit (_X), so ctype['A'+1] should contain the value:
_U + _X = 01 + 0200 = 0201
CHARSETS_AVAILABLE and
COMPILED_CHARSETS lists in configure.in.
If the sorting rules for your language are too complex to be handled
with the simple sort_order[] table, you need to use the string
collating functions.
Right now the best documentation on this is the character sets that are already implemented. Look at the big5, czech, gbk, sjis, and tis160 character sets for examples.
You must specify the strxfrm_multiply_MYSET=N value in the
special comment at the top of the file. N should be set to
the maximum ratio the strings may grow during my_strxfrm_MYSET (it
must be a positive integer).
If your character set includes multi-byte characters, you need to use the multi-byte character functions.
Right now the best documentation on this is the character sets that are already implemented. Look at the euc_kr, gb2312, gbk, sjis and ujis character sets for examples.
You must specify the mbmaxlen_MYSET=N value in the
special comment at the top of the file. N should be set to
the size in bytes of the largest character in the set.
MySQL Version 3.22 has a 4G limit on table size. With the new
MyISAM in MySQL Version 3.23 the maximum table size is
pushed up to 8 million terabytes (2 ^ 63 bytes).
Note, however, that operating systems have their own file size limits. Here are some examples:
| Operating System | File Size Limit |
| Linux-Intel 32 bit@tab 2G, 4G or bigger depending on Linux version | |
| Linux-Alpha | 8T (?) |
| Solaris 2.5.1 | 2G (possible 4G with patch) |
| Solaris 2.6 | 4G |
| Solaris 2.7 Intel | 4G |
| Solaris 2.7 ULTRA-SPARC | 8T (?) |
On Linux 2.2 you can get bigger tables than 2G by using the LFS patch for the ext2 file system. On Linux 2.4 there exists also patches for ReiserFS to get support for big files.
This means that the table size for MySQL is normally limited by the operating system.
By default, MySQL tables have a maximum size of about 4G. You can
check the maximum table size for a table with the SHOW TABLE STATUS
command or with the myisamchk -dv table_name.
See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
If you need bigger tables than 4G (and your operating system supports
this), you should set the AVG_ROW_LENGTH and MAX_ROWS
parameter when you create your table. See section 7.7 CREATE TABLE Syntax. You can
also set these later with ALTER TABLE. See section 7.8 ALTER TABLE Syntax.
If your big table is going to be read-only, you could use
myisampack to merge and compress many tables to one.
myisampack usually compresses a table by at least 50%, so you can
have, in effect, much bigger tables. See section 14.10 The MySQL Compressed Read-only Table Generator.
You can go around the operating system file limit for MyISAM data
files by using the RAID option. See section 7.7 CREATE TABLE Syntax.
Another solution can be the included MERGE library, which allows you to handle a collection of identical tables as one. See section 8.2 MERGE Tables.
One way replication can be used is to increase both robustness and speed. For robustness you can have two systems and can switch to the backup if you have problems with the master. The extra speed is achieved by sending a part of the non-updating queries to the replica server. Of course this only works if non-updating queries dominate, but that is the normal case.
Starting in Version 3.23.15, MySQL supports one-way replication internally. One server acts as the master, while the other acts as the slave. Note that one server could play the roles of master in one pair and slave in the other. The master server keeps a binary log of updates and an index file to binary logs to keep track of log rotation. The slave upon connecting informs the master where it left off since the last successfully propagated update, catches up on the updates, and then blocks and waits for the master to notify it of the new updates.
Note that if you are replicating a database, all updates to this database should be done through the master!
On older servers one can use the update log to do simple replication. See section 21.1 Database Replication with Update Log.
MySQL internal replication uses the master-slave approach. One
server is designated as the master, while the other (or others) as
slave(s). The master keeps a binary log of updates. See section 21.4 The Binary Log.
The slave connects to the master, catches up on the missed updates, and
then starts receiving updates immediately as they come to the master. If
the connection is lost, the slave will reconnect. If the master goes
down, the slave will keep trying to connect every
master-connect-retry seconds until the master comes back up and
the connection can be established. The slave keeps track of where it
left off in the replication process, so it can use the information in case
it goes down and gets restarted later.
Below is a quick HOWTO on how to set up replication on your current system:
FILE
privilege and permission to connect from all the slaves. If the user is
only doing replication, you don't need to grant him other privileges.
LOAD TABLE FROM MASTER. Until Version 3.23.23, though, it has a serious
bug, and we recommend that you do not use it until you have upgraded.
my.cnf on the master add log-bin and restart it. Make
sure there are no important updates to the master between the time you
have taken the snapshot and the time the master is restarted with
log-bin option.
my.cnf on the slave(s):
master-host=<hostname of the master> master-user=<replication user name> master-password=<replication user password>replacing the values in <> with what is relevant to your system. Starting in Version 3.23.26, you must also have on both master and slave
server-id=<some unique number between 1 and 2^32-1>
server-id must be different for each server participating in
replication. If you don't specify a server-id, it will be set to
1 if you have not defined master-host, else it will be set to 2.
After you have done the above, the master and the slave(s) should be in sync.
Below is an explanation of what is supported and what is not:
AUTO_INCREMENT,
LAST_INSERT_ID, and TIMESTAMP values.
LOAD DATA INFILE will be handled properly as long as the file
still resides on the master server at the time of update
propagation. LOAD LOCAL DATA INFILE will be skipped.
SLAVE STOP, then
check Slave_open_temp_tables variable to see if it is 0, then issue
mysqladmin shutdown. If the number is not 0, restart the slave thread
with SLAVE START and see
if you have better luck next time. There will be a cleaner solution, but it
has to wait until version 4.0.
In earlier versions temporary tables are not being replicated properly - we
recommend that you either upgrade, or execute SET SQL_LOG_BIN=0 on
your clients before all queries with temp tables.
log-slave-updates enabled.
Note, however, that many queries will not work right in this kind of
setup unless your client code is written to take care of the potential
problems that can happen from updates that occur in different sequence
on different servers. Note that the log format has changed in Version 3.23.26
so that pre-3.23.26 slaves will not be able to read it.
.err file. You should
then connect to the slave manually, fix the cause of the error
(for example, non-existent table), and then run SLAVE START sql command (available starting in Version 3.23.16). In Version 3.23.15, you will have
to restart the server.
master-connect-retry (default
60) seconds. Because of this, it is safe to shut down the master, and
then restart it after a while. The slave will also be able to deal with
network connectivity outages.
master-port parameter in my.cnf .
replicate-do-db directives in
my.cnf or just exclude a set of databases with
replicate-ignore-db. Note that up until Version 3.23.23, there was a bug
that did not properly deal with LOAD DATA INFILE if you did it in
a database that was excluded from replication.
SET SQL_LOG_BIN = 0 will turn off
replication (binary) logging on the master, and SET SQL_LOG_BIN =
1 will turn in back on - you must have the process privilege to do
this.
FLUSH MASTER
and FLUSH SLAVE commands. In Version 3.23.26 we have renamed them to
RESET MASTER and RESET SLAVE respectively to clarify
what they do. The old FLUSH variants still work, though for
compatibility.
LOAD TABLE FROM MASTER for
network backup and to set up replication initially.
CHANGE MASTER
TO.
binlog-ignore-db.
replicate-rewrite-db to tell
the slave to apply updates from one database on the master to the one
with a different name on the slave.
PURGE MASTER LOGS TO 'log-name'
to get rid of old logs while the slave is running.
If you are using replication, we recommend you to use MySQL Version 3.23.28 or later. Older versions work, but they do have some bugs and are missing some features.
On both master and slave you need to use the server-id option.
This sets an unique replication id. You should pick a unique value in the
range between 1 to 2^32-1 for each master and slave.
Example: server-id=3
The following table has the options you can use for the MASTER:
| Option | Description |
log-bin=filename |
Write to a binary update log to the specified location. Note that if you
give it a parameter with an extension
(for example, log-bin=/mysql/logs/replication.log ) versions up to 3.23.24
will not work right during replication if you do FLUSH LOGS . The
problem is fixed in Version 3.23.25. If you are using this kind of log name,
FLUSH LOGS will be ignored on binlog. To clear the log, run
FLUSH MASTER, and do not forget to run FLUSH SLAVE on all
slaves. In Version 3.23.26 and in later versions you should use RESET MASTER
and RESET SLAVE
|
log-bin-index=filename |
Because the user could issue the FLUSH LOGS command, we need to
know which log is currently active and which ones have been rotated out
and in what sequence. This information is stored in the binary log index file.
The default is `hostname`.index. You can use this option if you want to
be a rebel. (Example: log-bin-index=db.index)
|
sql-bin-update-same |
If set, setting SQL_LOG_BIN to a value will automatically set
SQL_LOG_UPDATE to the same value and vice versa.
|
binlog-do-db=database_name |
Tells the master it should log updates for the specified database, and
exclude all others not explicitly mentioned.
(Example: binlog-do-db=some_database)
|
binlog-ignore-db=database_name |
Tells the master that updates to the given database should not be logged
to the binary log (Example: binlog-ignore-db=some_database)
|
The following table has the options you can use for the SLAVE:
| Option | Description |
master-host=host |
Master hostname or IP address for replication. If not set, the slave
thread will not be started.
(Example: master-host=db-master.mycompany.com)
|
master-user=username |
The user the slave thread will us for authentication when connecting to
the master. The user must have FILE privilege. If the master user
is not set, user test is assumed. (Example:
master-user=scott)
|
master-password=password |
The password the slave thread will authenticate with when connecting to
the master. If not set, an empty password is assumed. (Example:
master-password=tiger)
|
master-port=portnumber |
The port the master is listening on. If not set, the compiled setting of
MYSQL_PORT is assumed. If you have not tinkered with
configure options, this should be 3306. (Example:
master-port=3306)
|
master-connect-retry=seconds |
The number of seconds the slave thread will sleep before retrying to
connect to the master in case the master goes down or the connection is
lost. Default is 60. (Example: master-connect-retry=60)
|
master-info-file=filename |
The location of the file that remembers where we left off on the master
during the replication process. The default is master.info in the data
directory. Sasha: The only reason I see for ever changing the default
is the desire to be rebelious. (Example:
master-info-file=master.info)
|
replicate-do-table=db_name.table_name |
Tells the slave thread to restrict replication to the specified database.
To specify more than one table, use the directive multiple times,
once for each table. .
(Example: replicate-do-table=some_db.some_table)
|
replicate-ignore-table=db_name.table_name |
Tells the slave thread to not replicate to the specified table. To
specify more than one table to ignore, use the directive multiple
times, once for each table.(Example:
replicate-ignore-table=db_name.some_table)
|
replicate-wild-do-table=db_name.table_name |
Tells the slave thread to restrict replication to the tables that match the
specified wildcard pattern. .
To specify more than one table, use the directive multiple times,
once for each table. .
(Example: replicate-do-table=foo%.bar% will replicate only updates
to tables in all databases that start with foo and whose table names
start with bar)
|
replicate-wild-ignore-table=db_name.table_name |
Tells the slave thread to not replicate to the tables that match the given
wild card pattern. To
specify more than one table to ignore, use the directive multiple
times, once for each table.(Example:
replicate-ignore-table=foo%.bar% - will not upates to tables in all databases that start with foo and whose table names
start with bar)
|
replicate-ignore-db=database_name |
Tells the slave thread to not replicate to the specified database. To
specify more than one database to ignore, use the directive multiple
times, once for each database. This option will not work if you use cross
database updates. If you need cross database updates to work, make sure
you have 3.23.28 or later, and use
replicate-wild-ignore-table=db_name.%(Example:
replicate-ignore-db=some_db)
|
replicate-do-db=database_name |
Tells the slave thread to restrict replication to the specified database.
To specify more than one database, use the directive multiple times,
once for each database. Note that this will only work if you do not use
cross-database queries such as UPDATE some_db.some_table SET
foo='bar' while having selected a different or no database. If you need
cross database updates to work, make sure
you have 3.23.28 or later, and use
replicate-wild-do-table=db_name.%
(Example: replicate-do-db=some_db)
|
log-slave-updates | Tells the slave to log the updates from the slave thread to the binary log. Off by default. You will need to turn it on if you plan to daisy-chain the slaves. |
replicate-rewrite-db=from_name->to_name |
Updates to a database with a different name than the original (Example:
replicate-rewrite-db=master_db_name->slave_db_name
|
skip-slave-start |
Tells the slave server not to start the slave on the startup. The user
can start it later with SLAVE START.
|
Replication can be controlled through the SQL interface. Below is the summary of commands:
| Command | Description |
SLAVE START
| Starts the slave thread. (Slave) |
SLAVE STOP
| Stops the slave thread. (Slave) |
SET SQL_LOG_BIN=0
| Disables update logging if the user has process privilege. Ignored otherwise. (Master) |
SET SQL_LOG_BIN=1
| Re-enables update logging if the user has process privilege. Ignored otherwise. (Master) |
RESET MASTER
| Deletes all binary logs listed in the index file, resetting the binlog
index file to be empty. In pre-3.23.26 versions, FLUSH MASTER (Master)
|
RESET SLAVE
| Makes the slave forget its replication position in the master
logs. In pre 3.23.26 versions the command was called
FLUSH SLAVE(Slave)
|
LOAD TABLE tblname FROM MASTER
| Downloads a copy of the table from master to the slave. (Slave) |
CHANGE MASTER TO master_def_list
| Changes the master parameters to the values specified in
master_def_list and restarts the slave thread. master_def_list
is a comma-separated list of master_def where master_def is
one of the following: MASTER_HOST, MASTER_USER,
MASTER_PASSWORD, MASTER_PORT, MASTER_CONNECT_RETRY,
MASTER_LOG_FILE, MASTER_LOG_POS. Example:
CHANGE MASTER TO MASTER_HOST='master2.mycompany.com', MASTER_USER='replication', MASTER_PASSWORD='bigs3cret', MASTER_PORT=3306;You only need to specify the values that need to be changed. The values that you omit will stay the same with the exception of when you change the host or the port. In that case, the slave will assume that since you are connecting to a different host or a different port, the master is different. Therefore, the old values of log and position are not applicable anymore, and will automatically be reset to an empty string and 0, respectively (the start values). Note that if you restart the slave, it will remember its last master. If this is not desirable, you should delete the `master.info' file before restarting, and the slave will read its master from my.cnf or the
command line. (Slave)
|
SHOW MASTER STATUS
| Provides status information on the binlog of the master. (Master) |
SHOW SLAVE STATUS
| Provides status information on essential parameters of the slave thread. (Slave) |
SHOW MASTER LOGS
| Only available starting in Version 3.23.28. Lists the binary logs on the master. You should use this command
prior to PURGE MASTER LOGS TO to find out how far you should go.
|
PURGE MASTER LOGS TO 'logname'
| Available starting in Version 3.23.28. Deletes all the
replication logs that are listed in the log
index as being prior to the specified log, and removed them from the
log index, so that the given log now becomes first. Example:
PURGE MASTER LOGS TO 'mysql-bin.010'This command will do nothing and fail with an error if you have an active slave that is currently reading one of the logs you are trying to delete. However, if you have a dormant slave, and happen to purge one of the logs it wants to read, the slave will be unable to replicate once it comes up. The command is safe to run while slaves are replicating - you do not need to stop them. You must first check all the slaves with SHOW SLAVE STATUS to
see which log they are on, then do a listing of the logs on the
master with SHOW MASTER LOGS, find the earliest log among all
the slaves (if all the slaves are up to date, this will be the
last log on the list), backup all the logs you are about to delete
(optional) and purge up to the target log.
|
Q: Why do I sometimes see more than one Binlog_Dump thread on
the master after I have restarted the slave?
A: Binlog_Dump is a continuous process that is handled by the
server in the following way:
pthread_cond_wait(),
from which we can be awakened either by an update or a kill.
Binlog_dump loop.
So if the slave thread stops on the slave, the corresponding
Binlog_Dump thread on the master will not notice it until after
at least one update to the master (or a kill), which is needed to wake
it up from pthread_cond_wait(). In the meantime, the slave
could have opened another connection, which resulted in another
Binlog_Dump thread.
The above problem should not be present in Version 3.23.26 and later versions.
In Version 3.23.26 we added server-id to each replication server, and
now all the old zombie threads are killed on the master when a new replication thread
connects from the same slave
Q: How do I rotate replication logs?
A: In Version 3.23.28 you should use PURGE MASTER LOGS TO
command after determining which logs can be deleted, and optionally
backing them up first. In earlier versions the process is much more
painful, and cannot be safely done without stopping all the slaves in
the case that you plan to re-use log names .
You will need to stop the slave threads, edit the binary log index
file, delete all the old logs, restart the master, start slave threads,
and then remove the old log files.
Q: How do I upgrade on a hot replication setup?
A: If you are upgrading pre-3.23.26 versions, you should just
lock the master tables, let the slave catch up, then run FLUSH
MASTER on the master, and FLUSH SLAVE on the slave to reset the
logs, then restart new versions of the master and the slave. Note that
the slave can stay down for some time - since the master is logging
all the updates, the slave will be able to catch up once it is up and
can connect.
We plan to make post 3.23.26 versions to be backwards compatible for replication down to Version 3.23.26, so upgrade should be just a matter of plug and play. Of course, as one joke goes, plug and play works usually only 50% of the time - just the plug part. We hope to do much better than that, though.
Q: What issues should I be aware of when setting up two-way replication?
A: MySQL replication currently does not support any locking protocol between master and slave to guarantee the atomicity of a distributed (cross-server) update. In in other words, it is possible for client A to make an update to co-master 1, and in the meantime, before it propagates to co-master 2, client B could make an update to co-master 2 that will make the update of client A work differently than it did on co-master 1. Thus when the update of client A will make it to co-master 2, it will produce tables that will be different than what you have on co-master 1, even after all the updates from co-master 2 have also propagated. So you should not co-chain two servers in a two-way replication relationship, unless you are sure that you updates can safely happen in any order, or unless you take care of mis-ordered updates somehow in the client code.
Until we implement server_id variable, you cannot have more than
two servers in a co-master replication relationship, and you must
run mysqld without log-slave-updates (default) to avoid
infinite update loops.
You must also realize that two-way replication actually does not improve performance very much, if at all, as far as updates are concerned. Both servers need to do the same amount of updates each, as you would have one server do. The only difference is that there will be a little less lock contention, because the updates originating on another server will be serialized in one slave thread. This benefit, though, might be offset by network delays.
Q: How can I use replication to improve performance of my system?
A: You should set up one server as the master, and direct all writes to it, and configure as many slaves as you have the money and rackspace for, distributing the reads among the master and the slaves.
Q: What should I do to prepare my client code to use performance-enhancing replication?
A: If the part of your code that is responsible for database access has been properly abstracted/modularized, converting it to run with the replicated setup should be very smooth and easy - just change the implementation of your database access to read from some slave or the master, and to awlays write to the master. If your code does not have this level of abstraction, setting up a replicated system will give you an opportunity/motivation to it clean up. You should start by creating a wrapper library /module with the following functions:
safe_writer_connect()
safe_reader_connect()
safe_reader_query()
safe_writer_query()
safe_ means that the function will take care of handling all
the error conditions.
You should then convert your client code to use the wrapper library.
It may be a painful and scary process at first, but it will pay off in
the long run. All applications that follow the above pattern will be
able to take advantage of one-master/many slaves solution. The
code will be a lot easier to maintain, and adding troubleshooting
options will be trivial. You will just need to modify one or two
functions, for example, to log how long each query took, or which
query, among your many thousands, gave you an error. If you have written a lot of code already,
you may want to automate the conversion task by using Monty's
replace utility, which comes with the standard distribution of
MySQL, or just write your own Perl script. Hopefully, your
code follows some recognizable pattern. If not, then you are probably
better off re-writing it anyway, or at least going through and manually
beating it into a pattern.
Note that, of course, you can use different names for the functions. What is important is having unified interface for connecting for reads, connecting for writes, doing a read, and doing a write.
Q: When and how much can MySQL replication improve the performance
of my system?
A: MySQL replication is most beneficial for a system with frequent reads and not so frequent writes. In theory, by using a one master/many slaves setup you can scale by adding more slaves until you either run out of network bandwidth, or your update load grows to the point that the master cannot handle it.
In order to determine how many slaves you can get before the added
benefits begin to level out, and how much you can improve performance
of your site, you need to know your query patterns, and empirically
(by benchmarking) determine the relationship between the throughput
on reads (reads per second, or max_reads) and on writes
max_writes) on a typical master and a typical slave. The
example below will show you a rather simplified calculation of what you
can get with replication for our imagined system.
Let's say our system load consists of 10% writes and 90% reads, and we
have determined that max_reads = 1200 - 2 * max_writes,
or in other words, our system can do 1200 reads per second with no
writes, our average write is twice as slow as average read,
and the relationship is
linear. Let us suppose that our master and slave are of the same
capacity, and we have N slaves and 1 master. Then we have for each
server (master or slave):
reads = 1200 - 2 * writes (from bencmarks)
reads = 9* writes / (N + 1) (reads split, but writes go
to all servers)
9*writes/(N+1) + 2 * writes = 1200
writes = 1200/(2 + 9/(N+1)
So if N = 0, which means we have no replication, our system can handle 1200/11, about 109 writes per second (which means we will have 9 times as many reads to the nature of our application).
If N = 1, we can get up to 184 writes per second.
If N = 8, we get up to 400.
If N = 17, 480 writes.
Eventually as N approaches infinity (and our budget negative infinity), we can get very close to 600 writes per second, increasing system throughput about 5.5 times. However, with only 8 servers, we increased it almost 4 times already.
Note that our computations assumed infinite network bandwidth, and neglected several other factors that could turn out to be signficant on your system. In many cases, you may not be able to make a computation similar to the one above that will accurately predict what will happen on your system if you add N replication slaves. However, answering the following questions should help you decided whether and how much, if at all, the replication will improve the performance of your system:
Q: How can I use replication to provide redundancy/high availability?
A: With the currently available features, you would have to set up a master and a slave (or several slaves), and write a script that will monitor the master to see if it is up, and instruct your applications and the slaves of the master change in case of failure. Some suggestions:
CHANGE MASTER TO command.
nsupdate to dynamically update your DNS.
log-bin option and without
log-slave-updates. This way the slave will be ready to become a
master as soon as you issue STOP SLAVE; RESET MASTER, and
CHANGE MASTER TO on the other slaves. It will also help you catch
spurious updates that may happen because of misconfiguration of the
slave (ideally, you want to configure access rights so that no client
can update the slave, except for the slave thread) combined with the
bugs in your client programs (they should never update the slave
directly).
We are currently working on intergrating an automatic master election system into MySQL, but until it is ready, you will have to create your own monitoring tools.
Optimization is a complicated task because it ultimately requires understanding of the whole system. While it may be possible to do some local optimizations with small knowledge of your system/application, the more optimal you want your system to become the more you will have to know about it.
So this chapter will try to explain and give some examples of different ways to optimize MySQL. But remember that there are always some (increasingly harder) additional ways to make the system even faster.
The most important part for getting a system fast is of course the basic design. You also need to know what kinds of things your system will be doing, and what your bottlenecks are.
The most common bottlenecks are:
We start with the system level things since some of these decisions have to be made very early. In other cases a fast look at this part may suffice because it not that important for the big gains. However, it is always nice to have a feeling about how much one could gain by changing things at this level.
The default OS to use is really important! To get the most use of multiple CPU machines one should use Solaris (because the threads works really nice) or Linux (because the 2.2 kernel has really good SMP support). Also on 32-bit machines Linux has a 2G file size limit by default. Hopefully this will be fixed soon when new filesystems are released (XFS/Reiserfs). If you have a desperate need for files bigger than 2G on Linux-intel 32 bit, you should get the LFS patch for the ext2 file system.
Because we have not run MySQL in production on that many platforms, we advice you to test your intended platform before choosing it, if possible.
--skip-locking MySQL option to avoid external
locking. Note that this will not impact MySQL's functionality as
long as you only run one server. Just remember to take down the server (or
lock relevant parts) before you run myisamchk. On some system
this switch is mandatory because the external locking does not work in any
case.
The --skip-locking option is on by default when compiling with
MIT-pthreads, because flock() isn't fully supported by
MIT-pthreads on all platforms.
The only case when you can't use --skip-locking is if you run
multiple MySQL servers (not clients) on the same data, or run
myisamchk on the table without first flushing and locking the
mysqld server tables first.
You can still use LOCK TABLES/UNLOCK TABLES even if you
are using --skip-locking
Most of the following tests are done on Linux with the MySQL benchmarks, but they should give some indication for other operating systems and workloads.
You get the fastest executable when you link with -static.
On Linux, you will get the fastest code when compiling with pgcc
and -O6. To compile `sql_yacc.cc' with these options, you
need about 200M memory because gcc/pgcc needs a lot of memory to
make all functions inline. You should also set CXX=gcc when
configuring MySQL to avoid inclusion of the libstdc++
library (it is not needed). Note that with some versions of pgcc,
the resulting code will only run on true Pentium processors, even if you
use the compiler option that you want the resulting code to be working on
all x586 type processors (like AMD).
By just using a better compiler and/or better compiler options you can get a 10-30 % speed increase in your application. This is particularly important if you compile the SQL server yourself!
We have tested both the Cygnus CodeFusion and Fujitsu compilers, but when we tested them, neither was sufficiently bug free to allow MySQL to be compiled with optimizations on.
When you compile MySQL you should only include support for the
character sets that you are going to use. (Option --with-charset=xxx).
The standard MySQL binary distributions are compiled with support
for all character sets.
Here is a list of some mesurements that we have done:
pgcc and compile everything with -O6, the
mysqld server is 11% faster than with gcc versions
older than gcc 2.95.2.
-static), the result is 13%
slower. Note that you still can use a dynamic linked MySQL
library. It is only the server that is critical for performance.
localhost,
MySQL will, by default, use sockets).
gcc 2.7.3 is 13% faster than Sun Pro C++ 4.2.
The MySQL-Linux distribution provided by MySQL AB used to be
compiled with pgcc, but we had to go back to regular gcc because
of a bug in pgcc that would generate the code that does not run
on AMD. We will continue using gcc until that bug is resolved. In the
meantime, if you have a non-AMD machine, you can get a faster binary by
compiling with pgcc. The standard MySqL Linux binary is linked
statically to get it faster and more portable.
hdparm -m 16 -d 1Note that the performance/reliability when using the above depends on your hardware, so we strongly suggest that you test your system throughly after using
hdparm! Please consult the hdparm
man page for more information! If hdparm is not used wisely,
filesystem corruption may result. Backup everything before experimenting!
You can move tables and databases from the database directory to other locations and replace them with symbolic links to the new locations. You might want to do this, for example, to move a database to a file system with more free space.
If MySQL notices that a table is symbolically linked, it will
resolve the symlink and use the table it points to instead. This works
on all systems that support the realpath() call (at least Linux
and Solaris support realpath())! On systems that don't support
realpath(), you should not access the table through the real path
and through the symlink at the same time! If you do, the table will be
inconsistent after any update.
MySQL doesn't that you link one directory to multiple
databases. Replacing a database directory with a symbolic link will
work fine as long as you don't make a symbolic link between databases.
Suppose you have a database db1 under the MySQL data
directory, and then make a symlink db2 that points to db1:
shell> cd /path/to/datadir shell> ln -s db1 db2
Now, for any table tbl_a in db1, there also appears to be
a table tbl_a in db2. If one thread updates db1.tbl_a
and another thread updates db2.tbl_a, there will be problems.
If you really need this, you must change the following code in `mysys/mf_format.c':
if (flag & 32 || (!lstat(to,&stat_buff) && S_ISLNK(stat_buff.st_mode)))
to
if (1)
On Windows you can use internal symbolic links to directories by compiling
MySQL with -DUSE_SYMDIR. This allows you to put different
databases on different disks. See section 4.13.6 Splitting Data Across Different Disks Under Windows.
You can get the default buffer sizes used by the mysqld server
with this command:
shell> mysqld --help
This command produces a list of all mysqld options and configurable
variables. The output includes the default values and looks something
like this:
Possible variables for option --set-variable (-O) are: back_log current value: 5 bdb_cache_size current value: 1048540 binlog_cache_size current_value: 32768 connect_timeout current value: 5 delayed_insert_timeout current value: 300 delayed_insert_limit current value: 100 delayed_queue_size current value: 1000 flush_time current value: 0 interactive_timeout current value: 28800 join_buffer_size current value: 131072 key_buffer_size current value: 1048540 lower_case_table_names current value: 0 long_query_time current value: 10 max_allowed_packet current value: 1048576 max_binlog_cache_size current_value: 4294967295 max_connections current value: 100 max_connect_errors current value: 10 max_delayed_threads current value: 20 max_heap_table_size current value: 16777216 max_join_size current value: 4294967295 max_sort_length current value: 1024 max_tmp_tables current value: 32 max_write_lock_count current value: 4294967295 myisam_sort_buffer_size current value: 8388608 net_buffer_length current value: 16384 net_retry_count current value: 10 net_read_timeout current value: 30 net_write_timeout current value: 60 query_buffer_size current value: 0 record_buffer current value: 131072 slow_launch_time current value: 2 sort_buffer current value: 2097116 table_cache current value: 64 thread_concurrency current value: 10 tmp_table_size current value: 1048576 thread_stack current value: 131072 wait_timeout current value: 28800
If there is a mysqld server currently running, you can see what
values it actually is using for the variables by executing this command:
shell> mysqladmin variables
You can find a full description for all variables in the SHOW VARIABLES
section in this manual. See section 7.28.4 SHOW VARIABLES.
You can also see some statistics from a running server by issuing the command
SHOW STATUS. See section 7.28.3 SHOW Status Information.
MySQL uses algorithms that are very scalable, so you can usually run with very little memory. If you, however, give MySQL more memory, you will normally also get better performance.
When tuning a MySQL server, the two most important variables to use
are key_buffer_size and table_cache. You should first feel
confident that you have these right before trying to change any of the
other variables.
If you have much memory (>=256M) and many tables and want maximum performance with a moderate number of clients, you should use something like this:
shell> safe_mysqld -O key_buffer=64M -O table_cache=256 \
-O sort_buffer=4M -O record_buffer=1M &
If you have only 128M and only a few tables, but you still do a lot of sorting, you can use something like:
shell> safe_mysqld -O key_buffer=16M -O sort_buffer=1M
If you have little memory and lots of connections, use something like this:
shell> safe_mysqld -O key_buffer=512k -O sort_buffer=100k \
-O record_buffer=100k &
or even:
shell> safe_mysqld -O key_buffer=512k -O sort_buffer=16k \
-O table_cache=32 -O record_buffer=8k -O net_buffer=1K &
When you have installed MySQL, the `Docs' directory will
contain some different my.cnf example files, `my-huge.cnf',
`my-large.cnf', `my-medium.cnf', and `my-small.cnf', you can
use as a base to optimize your system.
If there are very many connections, ``swapping problems'' may occur unless
mysqld has been configured to use very little memory for each
connection. mysqld performs better if you have enough memory for all
connections, of course.
Note that if you change an option to mysqld, it remains in effect only
for that instance of the server.
To see the effects of a parameter change, do something like this:
shell> mysqld -O key_buffer=32m --help
Make sure that the --help option is last; otherwise, the effect of any
options listed after it on the command line will not be reflected in the
output.
table_cache, max_connections, and max_tmp_tables
affect the maximum number of files the server keeps open. If you
increase one or both of these values, you may run up against a limit
imposed by your operating system on the per-process number of open file
descriptors. However, you can increase the limit on many systems.
Consult your OS documentation to find out how to do this, because the
method for changing the limit varies widely from system to system.
table_cache is related to max_connections. For example,
for 200 concurrent running connections, you should have a table cache of
at least 200 * n, where n is the maximum number of tables
in a join.
The cache of open tables can grow to a maximum of table_cache
(default 64; this can be changed with the -O table_cache=#
option to mysqld). A table is never closed, except when the
cache is full and another thread tries to open a table or if you use
mysqladmin refresh or mysqladmin flush-tables.
When the table cache fills up, the server uses the following procedure to locate a cache entry to use:
A table is opened for each concurrent access. This means that
if you have two threads accessing the same table or access the table
twice in the same query (with AS) the table needs to be opened twice.
The first open of any table takes two file descriptors; each additional
use of the table takes only one file descriptor. The extra descriptor
for the first open is used for the index file; this descriptor is shared
among all threads.
You can check if your table cache is too small by checking the mysqld
variable opened_tables. If this is quite big, even if you
haven't done a lot of FLUSH TABLES, you should increase your table
cache. See section 7.28.3 SHOW Status Information.
If you have many files in a directory, open, close, and create operations will
be slow. If you execute SELECT statements on many different tables,
there will be a little overhead when the table cache is full, because for
every table that has to be opened, another must be closed. You can reduce
this overhead by making the table cache larger.
When you run mysqladmin status, you'll see something like this:
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
This can be somewhat perplexing if you only have 6 tables.
MySQL is multithreaded, so it may have many queries on the same table simultaneously. To minimize the problem with two threads having different states on the same file, the table is opened independently by each concurrent thread. This takes some memory and one extra file descriptor for the data file. The index file descriptor is shared between all threads.
The list below indicates some of the ways that the mysqld server
uses memory. Where applicable, the name of the server variable relevant
to the memory use is given:
key_buffer_size) is shared by all
threads; Other buffers used by the server are allocated as
needed. See section 12.2.3 Tuning Server Parameters.
thread_stack), a connection buffer (variable
net_buffer_length), and a result buffer (variable
net_buffer_length). The connection buffer and result buffer are
dynamically enlarged up to max_allowed_packet when needed. When
a query is running, a copy of the current query string is also allocated.
record_buffer).
BLOB columns are
stored on disk.
One problem in MySQL versions before Version 3.23.2 is that if a HEAP table
exceeds the size of tmp_table_size, you get the error The
table tbl_name is full. In newer versions this is handled by
automatically changing the in-memory (HEAP) table to a disk-based
(MyISAM) table as necessary. To work around this problem, you can
increase the temporary table size by setting the tmp_table_size
option to mysqld, or by setting the SQL option
SQL_BIG_TABLES in the client program. See section 7.33 SET Syntax. In MySQL Version 3.20, the maximum size of the
temporary table was record_buffer*16, so if you are using this
version, you have to increase the value of record_buffer. You can
also start mysqld with the --big-tables option to always
store temporary tables on disk. However, this will affect the speed of
many complicated queries.
malloc() and
free()).
3 * n is
allocated (where n is the maximum row length, not counting BLOB
columns). A BLOB uses 5 to 8 bytes plus the length of the BLOB
data. The ISAM/MyISAM table handlers will use one extra row
buffer for internal usage.
BLOB columns, a buffer is enlarged dynamically
to read in larger BLOB values. If you scan a table, a buffer as large
as the largest BLOB value is allocated.
mysqladmin flush-tables command closes all tables that are not in
use and marks all in-use tables to be closed when the currently executing
thread finishes. This will effectively free most in-use memory.
ps and other system status programs may report that mysqld
uses a lot of memory. This may be caused by thread-stacks on different
memory addresses. For example, the Solaris version of ps counts
the unused memory between stacks as used memory. You can verify this by
checking available swap with swap -s. We have tested
mysqld with commercial memory-leakage detectors, so there should
be no memory leaks.
You can find a discussion about different locking methods in the appendix. See section H.4 Locking methods.
All locking in MySQL is deadlock-free. This is managed by always requesting all needed locks at once at the beginning of a query and always locking the tables in the same order.
The locking method MySQL uses for WRITE locks works as follows:
The locking method MySQL uses for READ locks works as follows:
When a lock is released, the lock is made available to the threads in the write lock queue, then to the threads in the read lock queue.
This means that if you have many updates on a table, SELECT
statements will wait until there are no more updates.
To work around this for the case where you want to do many INSERT and
SELECT operations on a table, you can insert rows in a temporary
table and update the real table with the records from the temporary table
once in a while.
This can be done with the following code:
mysql> LOCK TABLES real_table WRITE, insert_table WRITE; mysql> insert into real_table select * from insert_table; mysql> TRUNCATE insert_table; mysql> UNLOCK TABLES;
You can use the LOW_PRIORITY options with INSERT if you
want to prioritize retrieval in some specific cases. See section 7.21 INSERT Syntax.
You could also change the locking code in `mysys/thr_lock.c' to use a single queue. In this case, write locks and read locks would have the same priority, which might help some applications.
The table locking code in MySQL is deadlock free.
MySQL uses table locking (instead of row locking or column
locking) on all table types, except BDB tables, to achieve a very
high lock speed. For large tables, table locking is MUCH better than
row locking for most applications, but there are, of course, some
pitfalls.
For BDB tables, MySQL only uses table locking if you
explicitely lock the table with LOCK TABLES or execute a command that
will modify every row in the table, like ALTER TABLE.
In MySQL Version 3.23.7 and above, you can insert rows into
MyISAM tables at the same time other threads are reading from
the table. Note that currently this only works if there are no holes after
deleted rows in the table at the time the insert is made.
Table locking enables many threads to read from a table at the same time, but if a thread wants to write to a table, it must first get exclusive access. During the update, all other threads that want to access this particular table will wait until the update is ready.
As updates on tables normally are considered to be more important than
SELECT, all statements that update a table have higher priority
than statements that retrieve information from a table. This should
ensure that updates are not 'starved' because one issues a lot of heavy
queries against a specific table. (You can change this by using
LOW_PRIORITY with the statement that does the update or
HIGH_PRIORITY with the SELECT statement.)
Starting from MySQL Version 3.23.7 one can use the
max_write_lock_count variable to force MySQL to
temporary give all SELECT statements, that wait for a table, a
higher priority after a specific number of inserts on a table.
Table locking is, however, not very good under the following senario:
SELECT that takes a long time to run.
UPDATE on a used table. This client
will wait until the SELECT is finished.
SELECT statement on the same table. As
UPDATE has higher priority than SELECT, this SELECT
will wait for the UPDATE to finish. It will also wait for the first
SELECT to finish!
Some possible solutions to this problem are:
SELECT statements to run faster. You may have to create
some summary tables to do this.
mysqld with --low-priority-updates. This will give
all statements that update (modify) a table lower priority than a SELECT
statement. In this case the last SELECT statement in the previous
scenario would execute before the INSERT statement.
INSERT, UPDATE, or DELETE
statement lower priority with the LOW_PRIORITY attribute.
mysqld with a low value for max_write_lock_count to give
READ locks after a certain number of WRITE locks.
SET SQL_LOW_PRIORITY_UPDATES=1.
See section 7.33 SET Syntax.
SELECT is very important with the
HIGH_PRIORITY attribute. See section 7.19 SELECT Syntax.
INSERT combined with SELECT,
switch to use the new MyISAM tables as these support concurrent
SELECTs and INSERTs.
INSERT and SELECT statements, the
DELAYED attribute to INSERT will probably solve your problems.
See section 7.21 INSERT Syntax.
SELECT and DELETE, the LIMIT
option to DELETE may help. See section 7.17 DELETE Syntax.
One of the most basic optimization is to get your data (and indexes) to take as little space on the disk (and in memory) as possible. This can give huge improvements because disk reads are faster and normally less main memory will be used. Indexing also takes less resources if done on smaller columns.
MySQL supports a lot of different table types and row formats. Choosing the right table format may give you a big performance gain. See section 8 MySQL Table Types.
You can get better performance on a table and minimize storage space using the techniques listed below:
MEDIUMINT is often better than INT.
NOT NULL if possible. It makes everything
faster and you save one bit per column. Note that if you really need
NULL in your application you should definitely use it. Just avoid
having it on all columns by default.
VARCHAR,
TEXT, or BLOB columns), a fixed-size record format is
used. This is faster but unfortunately may waste some space.
See section 8.1.2 MyISAM Table Formats.
Indexes are used to find rows with a specific value of one column fast. Without an index MySQL has to start with the first record and then read through the whole table until it finds the relevent rows. The bigger the table, the more this costs. If the table has an index for the colums in question, MySQL can quickly get a position to seek to in the middle of the data file without having to look at all the data. If a table has 1000 rows, this is at least 100 times faster than reading sequentially. Note that if you need to access almost all 1000 rows it is faster to read sequentially because we then avoid disk seeks.
All MySQL indexes (PRIMARY, UNIQUE, and
INDEX) are stored in B-trees. Strings are automatically prefix-
and end-space compressed. See section 7.35 CREATE INDEX Syntax.
Indexes are used to:
WHERE clause.
MAX() or MIN() value for a specific indexed
column. This is optimized by a preprocessor that checks if you are
using WHERE key_part_# = constant on all key parts < N. In this case
MySQL will do a single key lookup and replace the MIN()
expression with a constant. If all expressions are replaced with
constants, the query will return at once:
SELECT MIN(key_part2),MAX(key_part2) FROM table_name where key_part1=10
ORDER BY key_part_1,key_part_2 ). The
key is read in reverse order if all key parts are followed by DESC.
The index can also be used even if the ORDER BY doesn't match the index
exactly, as long as all the unused index parts and all the extra
are ORDER BY columns are constants in the WHERE clause. The
following queries will use the index to resolve the ORDER BY part:
SELECT * FROM foo ORDER BY key_part1,key_part2,key_part3; SELECT * FROM foo WHERE column=constant ORDER BY column, key_part1; SELECT * FROM foo WHERE key_part1=const GROUP BY key_part2;
SELECT key_part3 FROM table_name WHERE key_part1=1
Suppose you issue the following SELECT statement:
mysql> SELECT * FROM tbl_name WHERE col1=val1 AND col2=val2;
If a multiple-column index exists on col1 and col2, the
appropriate rows can be fetched directly. If separate single-column
indexes exist on col1 and col2, the optimizer tries to
find the most restrictive index by deciding which index will find fewer
rows and using that index to fetch the rows.
If the table has a multiple-column index, any leftmost prefix of the
index can be used by the optimizer to find rows. For example, if you
have a three-column index on (col1,col2,col3), you have indexed
search capabilities on (col1), (col1,col2), and
(col1,col2,col3).
MySQL can't use a partial index if the columns don't form a
leftmost prefix of the index. Suppose you have the SELECT
statements shown below:
mysql> SELECT * FROM tbl_name WHERE col1=val1; mysql> SELECT * FROM tbl_name WHERE col2=val2; mysql> SELECT * FROM tbl_name WHERE col2=val2 AND col3=val3;
If an index exists on (col1,col2,col3), only the first query
shown above uses the index. The second and third queries do involve
indexed columns, but (col2) and (col2,col3) are not
leftmost prefixes of (col1,col2,col3).
MySQL also uses indexes for LIKE comparisons if the argument
to LIKE is a constant string that doesn't start with a wild-card
character. For example, the following SELECT statements use indexes:
mysql> select * from tbl_name where key_col LIKE "Patrick%"; mysql> select * from tbl_name where key_col LIKE "Pat%_ck%";
In the first statement, only rows with "Patrick" <= key_col <
"Patricl" are considered. In the second statement, only rows with
"Pat" <= key_col < "Pau" are considered.
The following SELECT statements will not use indexes:
mysql> select * from tbl_name where key_col LIKE "%Patrick%"; mysql> select * from tbl_name where key_col LIKE other_col;
In the first statement, the LIKE value begins with a wild-card
character. In the second statement, the LIKE value is not a
constant.
Searching using column_name IS NULL will use indexes if column_name
is an index.
MySQL normally uses the index that finds the least number of rows. An
index is used for columns that you compare with the following operators:
=, >, >=, <, <=, BETWEEN, and a
LIKE with a non-wild-card prefix like 'something%'.
Any index that doesn't span all AND levels in the WHERE clause
is not used to optimize the query. In other words: To be able to use an
index, a prefix of the index must be used in every AND group.
The following WHERE clauses use indexes:
... WHERE index_part1=1 AND index_part2=2 AND other_column=3
... WHERE index=1 OR A=10 AND index=2 /* index = 1 OR index = 2 */
... WHERE index_part1='hello' AND index_part_3=5
/* optimized like "index_part1='hello'" */
... WHERE index1=1 and index2=2 or index1=3 and index3=3;
/* Can use index on index1 but not on index2 or index 3 */
These WHERE clauses do NOT use indexes:
... WHERE index_part2=1 AND index_part3=2 /* index_part_1 is not used */ ... WHERE index=1 OR A=10 /* Index is not used in both AND parts */ ... WHERE index_part1=1 OR index_part2=10 /* No index spans all rows */
Note that in some cases MySQL will not use an index, even if one would be available. Some of the cases where this happens are:
LIMIT to only retrieve
part of the rows, MySQL will use an index anyway, as it can
much more quickly find the few rows to return in the result.
First, one thing that affects all queries: The more complex permission system setup you have, the more overhead you get.
If you do not have any GRANT statements done, MySQL will
optimize the permission checking somewhat. So if you have a very high
volume it may be worth the time to avoid grants. Otherwise more
permission check results in a larger overhead.
If your problem is with some explicit MySQL function, you can always time this in the MySQL client:
mysql> select benchmark(1000000,1+1); +------------------------+ | benchmark(1000000,1+1) | +------------------------+ | 0 | +------------------------+ 1 row in set (0.32 sec)
The above shows that MySQL can execute 1,000,000 +
expressions in 0.32 seconds on a PentiumII 400MHz.
All MySQL functions should be very optimized, but there may be
some exceptions, and the benchmark(loop_count,expression) is a
great tool to find out if this is a problem with your query.
In most cases you can estimate the performance by counting disk seeks.
For small tables, you can usually find the row in 1 disk seek (as the
index is probably cached). For bigger tables, you can estimate that
(using B++ tree indexes) you will need: log(row_count) /
log(index_block_length / 3 * 2 / (index_length + data_pointer_length)) +
1 seeks to find a row.
In MySQL an index block is usually 1024 bytes and the data
pointer is usually 4 bytes. A 500,000 row table with an
index length of 3 (medium integer) gives you:
log(500,000)/log(1024/3*2/(3+4)) + 1 = 4 seeks.
As the above index would require about 500,000 * 7 * 3/2 = 5.2M, (assuming that the index buffers are filled to 2/3, which is typical) you will probably have much of the index in memory and you will probably only need 1-2 calls to read data from the OS to find the row.
For writes, however, you will need 4 seek requests (as above) to find where to place the new index and normally 2 seeks to update the index and write the row.
Note that the above doesn't mean that your application will slowly degenerate by N log N! As long as everything is cached by the OS or SQL server things will only go marginally slower while the table gets bigger. After the data gets too big to be cached, things will start to go much slower until your applications is only bound by disk-seeks (which increase by N log N). To avoid this, increase the index cache as the data grows. See section 12.2.3 Tuning Server Parameters.
SELECT Queries
In general, when you want to make a slow SELECT ... WHERE faster, the
first thing to check is whether or not you can add an index. See section 12.4 How MySQL Uses Indexes. All references between different tables
should usually be done with indexes. You can use the EXPLAIN command
to determine which indexes are used for a SELECT.
See section 7.29 EXPLAIN Syntax (Get Information About a SELECT).
Some general tips:
myisamchk
--analyze on a table after it has been loaded with relevant data. This
updates a value for each index part that indicates the average number of
rows that have the same value. (For unique indexes, this is always 1,
of course.). MySQL will use this to decide which index to
choose when you connect two tables with 'a non-constant expression'.
You can check the result from the analyze run by doing SHOW
INDEX FROM table_name and examining the Cardinality column.
myisamchk
--sort-index --sort-records=1 (if you want to sort on index 1). If you
have a unique index from which you want to read all records in order
according to that index, this is a good way to make that faster. Note,
however, that this sorting isn't written optimally and will take a long
time for a large table!
WHERE Clauses
The WHERE optimizations are put in the SELECT part here because
they are mostly used with SELECT, but the same optimizations apply for
WHERE in DELETE and UPDATE statements.
Also note that this section is incomplete. MySQL does many optimizations, and we have not had time to document them all.
Some of the optimizations performed by MySQL are listed below:
((a AND b) AND c OR (((a AND b) AND (c AND d)))) -> (a AND b AND c) OR (a AND b AND c AND d)
(a<b AND b=c) AND a=5 -> b>5 AND b=c AND a=5
(B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6) -> B=5 OR B=6
COUNT(*) on a single table without a WHERE is retrieved
directly from the table information. This is also done for any NOT NULL
expression when used with only one table.
SELECT statements are impossible and returns no rows.
HAVING is merged with WHERE if you don't use GROUP BY
or group functions (COUNT(), MIN()...).
WHERE is constructed to get a fast
WHERE evaluation for each sub-join and also to skip records as
soon as possible.
WHERE clause on a UNIQUE
index, or a PRIMARY KEY, where all index parts are used with constant
expressions and the index parts are defined as NOT NULL.
mysql> SELECT * FROM t WHERE primary_key=1;
mysql> SELECT * FROM t1,t2
WHERE t1.primary_key=1 AND t2.primary_key=t1.id;
ORDER BY and in GROUP
BY come from the same table, then this table is preferred first when
joining.
ORDER BY clause and a different GROUP BY
clause, or if the ORDER BY or GROUP BY contains columns
from tables other than the first table in the join queue, a temporary
table is created.
SQL_SMALL_RESULT, MySQL will use an in-memory
temporary table.
HAVING clause
are skipped.
Some examples of queries that are very fast:
mysql> SELECT COUNT(*) FROM tbl_name;
mysql> SELECT MIN(key_part1),MAX(key_part1) FROM tbl_name;
mysql> SELECT MAX(key_part2) FROM tbl_name
WHERE key_part_1=constant;
mysql> SELECT ... FROM tbl_name
ORDER BY key_part1,key_part2,... LIMIT 10;
mysql> SELECT ... FROM tbl_name
ORDER BY key_part1 DESC,key_part2 DESC,... LIMIT 10;
The following queries are resolved using only the index tree (assuming the indexed columns are numeric):
mysql> SELECT key_part1,key_part2 FROM tbl_name WHERE key_part1=val;
mysql> SELECT COUNT(*) FROM tbl_name
WHERE key_part1=val1 AND key_part2=val2;
mysql> SELECT key_part2 FROM tbl_name GROUP BY key_part1;
The following queries use indexing to retrieve the rows in sorted order without a separate sorting pass:
mysql> SELECT ... FROM tbl_name ORDER BY key_part1,key_part2,... mysql> SELECT ... FROM tbl_name ORDER BY key_part1 DESC,key_part2 DESC,...
DISTINCT
DISTINCT is converted to a GROUP BY on all columns,
DISTINCT combined with ORDER BY will in many cases also
need a temporary table.
When combining LIMIT # with DISTINCT, MySQL will stop
as soon as it finds # unique rows.
If you don't use columns from all used tables, MySQL will stop the scanning of the not used tables as soon as it has found the first match.
SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;
In the case, assuming t1 is used before t2 (check with EXPLAIN), then
MySQL will stop reading from t2 (for that particular row in t1)
when the first row in t2 is found.
LEFT JOIN and RIGHT JOIN
A LEFT JOIN B in MySQL is implemented as follows:
B is set to be dependent on table A and all tables
that A is dependent on.
A is set to be dependent on all tables (except B)
that are used in the LEFT JOIN condition.
LEFT JOIN conditions are moved to the WHERE clause.
WHERE optimizations are done.
A that matches the WHERE clause, but there
wasn't any row in B that matched the LEFT JOIN condition,
then an extra B row is generated with all columns set to NULL.
LEFT JOIN to find rows that don't exist in some
table and you have the following test: column_name IS NULL in the
WHERE part, where column_name is a column that is declared as
NOT NULL, then MySQL will stop searching after more rows
(for a particular key combination) after it has found one row that
matches the LEFT JOIN condition.
RIGHT JOIN is implemented analogously as LEFT JOIN.
The table read order forced by LEFT JOIN and STRAIGHT JOIN
will help the join optimizer (which calculates in which order tables
should be joined) to do its work much more quickly, as there are fewer
table permutations to check.
Note that the above means that if you do a query of type:
SELECT * FROM a,b LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
MySQL will do a full scan on b as the LEFT
JOIN will force it to be read before d.
The fix in this case is to change the query to:
SELECT * FROM b,a LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key) WHERE b.key=d.key
LIMIT
In some cases MySQL will handle the query differently when you are
using LIMIT # and not using HAVING:
LIMIT, MySQL
will use indexes in some cases when it normally would prefer to do a
full table scan.
LIMIT # with ORDER BY, MySQL will end the
sorting as soon as it has found the first # lines instead of sorting
the whole table.
LIMIT # with DISTINCT, MySQL will stop
as soon as it finds # unique rows.
GROUP BY can be resolved by reading the key in order
(or do a sort on the key) and then calculate summaries until the
key value changes. In this case LIMIT # will not calculate any
unnecessary GROUP BY's.
# rows to the client, it
will abort the query.
LIMIT 0 will always quickly return an empty set. This is useful
to check the query and to get the column types of the result columns.
LIMIT # to calculate how much
space is needed to resolve the query.
INSERT QueriesThe time to insert a record consists approximately of:
where the numbers are somewhat proportional to the overall time. This does not take into consideration the initial overhead to open tables (which is done once for each concurrently running query).
The size of the table slows down the insertion of indexes by N log N (B-trees).
Some ways to speed up inserts:
INSERT statements. This is much faster (many
times in some cases) than using separate INSERT statements.
INSERT DELAYED statement. See section 7.21 INSERT Syntax.
MyISAM you can insert rows at the same time
SELECTs are running if there are no deleted rows in the tables.
LOAD DATA INFILE. This
is usually 20 times faster than using a lot of INSERT statements.
See section 7.23 LOAD DATA INFILE Syntax.
LOAD DATA INFILE run even
faster when the table has many indexes. Use the following procedure:
CREATE TABLE. For example, using
mysql or Perl-DBI.
FLUSH TABLES statement or the shell command mysqladmin
flush-tables.
myisamchk --keys-used=0 -rq /path/to/db/tbl_name. This will
remove all usage of all indexes from the table.
LOAD DATA INFILE. This will not
update any indexes and will therefore be very fast.
myisampack
on it to make it smaller. See section 8.1.2.3 Compressed Table Characteristics.
myisamchk -r -q
/path/to/db/tbl_name. This will create the index tree in memory before
writing it to disk, which is much faster because it avoids lots of disk
seeks. The resulting index tree is also perfectly balanced.
FLUSH TABLES statement or the shell command mysqladmin
flush-tables.
LOAD DATA INFILE in some future
version of MySQL.
mysql> LOCK TABLES a WRITE; mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33); mysql> INSERT INTO a VALUES (8,26),(6,29); mysql> UNLOCK TABLES;The main speed difference is that the index buffer is flushed to disk only once, after all
INSERT statements have completed. Normally there would
be as many index buffer flushes as there are different INSERT
statements. Locking is not needed if you can insert all rows with a single
statement.
Locking will also lower the total time of multi-connection tests, but the
maximum wait time for some threads will go up (because they wait for
locks). For example:
thread 1 does 1000 inserts thread 2, 3, and 4 does 1 insert thread 5 does 1000 insertsIf you don't use locking, 2, 3, and 4 will finish before 1 and 5. If you use locking, 2, 3, and 4 probably will not finish before 1 or 5, but the total time should be about 40% faster. As
INSERT, UPDATE, and DELETE operations are very
fast in MySQL, you will obtain better overall performance by
adding locks around everything that does more than about 5 inserts or
updates in a row. If you do very many inserts in a row, you could do a
LOCK TABLES followed by an UNLOCK TABLES once in a while
(about each 1000 rows) to allow other threads access to the table. This
would still result in a nice performance gain.
Of course, LOAD DATA INFILE is much faster for loading data.
To get some more speed for both LOAD DATA INFILE and
INSERT, enlarge the key buffer. See section 12.2.3 Tuning Server Parameters.
UPDATE Queries
Update queries are optimized as a SELECT query with the additional
overhead of a write. The speed of the write is dependent on the size of
the data that is being updated and the number of indexes that are
updated. Indexes that are not changed will not be updated.
Also, another way to get fast updates is to delay updates and then do many updates in a row later. Doing many updates in a row is much quicker than doing one at a time if you lock the table.
Note that, with dynamic record format, updating a record to
a longer total length may split the record. So if you do this often,
it is very important to OPTIMIZE TABLE sometimes.
See section 7.11 OPTIMIZE TABLE Syntax.
DELETE Queries
If you want to delete all rows in the table, you should use
TRUNCATE table_name. See section 7.18 TRUNCATE Syntax.
The time to delete a record is exactly proportional to the number of indexes. To delete records more quickly, you can increase the size of the index cache. See section 12.2.3 Tuning Server Parameters.
Unsorted tips for faster systems:
thread_cache_size variable. See section 12.2.3 Tuning Server Parameters.
EXPLAIN
command. See section 7.29 EXPLAIN Syntax (Get Information About a SELECT).
SELECT queries on tables that are updated a
lot. This is to avoid problems with table locking.
MyISAM tables can insert rows in a table without deleted
rows at the same time another table is reading from it. If this is important
for you, you should consider methods where you don't have to delete rows
or run OPTIMIZE TABLE after you have deleted a lot of rows.
ALTER TABLE ... ORDER BY expr1,expr2... if you mostly
retrieve rows in expr1,expr2.. order. By using this option after big
changes to the table, you may be able to get higher performance.
SELECT * FROM table_name WHERE hash=MD5(concat(col1,col2))
AND col_1='constant' AND col_2='constant'
VARCHAR
or BLOB columns. You will get dynamic row length as soon as you
are using a single VARCHAR or BLOB column. See section 8 MySQL Table Types.
UPDATE table set count=count+1 where index_column=constant
is very fast!
This is really important when you use databases like MySQL that
only have table locking (multiple readers / single writers). This will
also give better performance with most databases, as the row locking
manager in this case will have less to do.
INSERT /*! DELAYED */ when you do not need to know when your
data is written. This speeds things up because many records can be written
with a single disk write.
INSERT /*! LOW_PRIORITY */ when you want your selects to be
more important.
SELECT /*! HIGH_PRIORITY */ to get selects that jump the
queue. That is, the select is done even if there is somebody waiting to
do a write.
INSERT statement to store many rows with one
SQL command (many SQL servers supports this).
LOAD DATA INFILE to load bigger amounts of data. This is
faster than normal inserts and will be even faster when myisamchk
is integrated in mysqld.
AUTO_INCREMENT columns to make unique values.
OPTIMIZE TABLE once in a while to avoid fragmentation when
using dynamic table format. See section 7.11 OPTIMIZE TABLE Syntax.
HEAP tables to get more speed when possible. See section 8 MySQL Table Types.
name instead of
customer_name in the customer table). To make your names portable
to other SQL servers you should keep them shorter than 18 characters.
MyISAM directly, you could
get a speed increase of 2-5 times compared to using the SQL interface.
To be able to do this the data must be on the same server as
the application, and usually it should only be accessed by one process
(because external file locking is really slow). One could eliminate the
above problems by introducing low-level MyISAM commands in the
MySQL server (this could be one easy way to get more
performance if needed). By carefully designing the database interface,
it should be quite easy to support this types of optimization.
DELAY_KEY_WRITE=1 will make the updating of
indexes faster, as these are not logged to disk until the file is closed.
The downside is that you should run myisamchk on these tables before
you start mysqld to ensure that they are okay if something killed
mysqld in the middle. As the key information can always be generated
from the data, you should not lose anything by using DELAY_KEY_WRITE.
You should definately benchmark your application and database to find out where the bottlenecks are. By fixing it (or by replacing the bottleneck with a 'dummy module') you can then easily identify the next bottleneck (and so on). Even if the overall performance for your application is sufficient, you should at least make a plan for each bottleneck, and decide how to solve it if someday you really need the extra performance.
For an example of portable benchmark programs, look at the MySQL benchmark suite. See section 13 The MySQL Benchmark Suite. You can take any program from this suite and modify it for your needs. By doing this, you can try different solutions to your problem and test which is really the fastest solution for you.
It is very common that some problems only occur when the system is very heavily loaded. We have had many customers who contact us when they have a (tested) system in production and have encountered load problems. In every one of these cases so far, it has been problems with basic design (table scans are NOT good at high load) or OS/Library issues. Most of this would be a LOT easier to fix if the systems were not already in production.
To avoid problems like this, you should put some effort into benchmarking your whole application under the worst possible load! You can use Sasha's recent hack for this - mysql-super-smack. As the name suggests, it can bring your system down to its knees if you ask it, so make sure to use it only on your developement systems.
MySQL keeps row data and index data in separate files. Many (almost all) other databases mix row and index data in the same file. We believe that the MySQL choice is better for a very wide range of modern systems.
Another way to store the row data is to keep the information for each column in a separate area (examples are SDBM and Focus). This will cause a performance hit for every query that accesses more than one column. Because this degenerates so quickly when more than one column is accessed, we believe that this model is not good for general purpose databases.
The more common case is that the index and data are stored together (like in Oracle/Sybase et al). In this case you will find the row information at the leaf page of the index. The good thing with this layout is that it, in many cases, depending on how well the index is cached, saves a disk read. The bad things with this layout are:
Because MySQL uses extremely fast table locking (multiple readers / single writers) the biggest remaining problem is a mix of a steady stream of inserts and slow selects on the same table.
We believe that for a huge number of systems the extremely fast performance in other cases make this choice a win. This case is usually also possible to solve by having multiple copies of the table, but it takes more effort and hardware.
We are also working on some extensions to solve this problem for some common application niches.
Because all SQL servers implement different parts of SQL, it takes work to write portable SQL applications. For very simple selects/inserts it is very easy, but the more you need the harder it gets. If you want an application that is fast with many databases it becomes even harder!
To make a complex application portable you need to choose a number of SQL servers that it should work with.
You can use the MySQL crash-me program/web-page http://www.mysql.com/information/crash-me.php to find functions, types, and limits you can use with a selection of database servers. Crash-me now tests far from everything possible, but it is still comprehensive with about 450 things tested.
For example, you shouldn't have column names longer than 18 characters if you want to be able to use Informix or DB2.
Both the MySQL benchmarks and crash-me programs are very database-independent. By taking a look at how we have handled this, you can get a feeling for what you have to do to write your application database-independent. The benchmarks themselves can be found in the `sql-bench' directory in the MySQL source distribution. They are written in Perl with DBI database interface (which solves the access part of the problem).
See http://www.mysql.com/information/benchmarks.html for the results from this benchmark.
As you can see in these results, all databases have some weak points. That is, they have different design compromises that lead to different behavior.
If you strive for database independence, you need to get a good feeling for each SQL server's bottlenecks. MySQL is VERY fast in retrieving and updating things, but will have a problem in mixing slow readers/writers on the same table. Oracle, on the other hand, has a big problem when you try to access rows that you have recently updated (until they are flushed to disk). Transaction databases in general are not very good at generating summary tables from log tables, as in this case row locking is almost useless.
To get your application really database-independent, you need to define an easy extendable interface through which you manipulate your data. As C++ is available on most systems, it makes sense to use a C++ classes interface to the databases.
If you use some specific feature for some database (like the
REPLACE command in MySQL), you should code a method for
the other SQL servers to implement the same feature (but slower). With
MySQL you can use the /*! */ syntax to add
MySQL-specific keywords to a query. The code inside
/**/ will be treated as a comment (ignored) by most other SQL
servers.
If REAL high performance is more important than exactness, as in some Web applications, a possibility is to create an application layer that caches all results to give you even higher performance. By letting old results 'expire' after a while, you can keep the cache reasonably fresh. This is quite nice in case of extremely high load, in which case you can dynamically increase the cache and set the expire timeout higher until things get back to normal.
In this case the table creation information should contain information of the initial size of the cache and how often the table should normally be refreshed.
During MySQL initial development, the features of MySQL were made to fit our largest customer. They handle data warehousing for a couple of the biggest retailers in Sweden.
From all stores, we get weekly summaries of all bonus card transactions, and we are expected to provide useful information for the store owners to help them find how their advertisement campaigns are affecting their customers.
The data is quite huge (about 7 million summary transactions per month), and we have data for 4-10 years that we need to present to the users. We got weekly requests from the customers that they want to get 'instant' access to new reports from this data.
We solved this by storing all information per month in compressed 'transaction' tables. We have a set of simple macros (script) that generates summary tables grouped by different criteria (product group, customer id, store ...) from the transaction tables. The reports are Web pages that are dynamically generated by a small Perl script that parses a Web page, executes the SQL statements in it, and inserts the results. We would have used PHP or mod_perl instead but they were not available at that time.
For graphical data we wrote a simple tool in C that can produce
GIFs based on the result of a SQL query (with some processing of the
result). This is also dynamically executed from the Perl script that
parses the HTML files.
In most cases a new report can simply be done by copying an existing script and modifying the SQL query in it. In some cases, we will need to add more fields to an existing summary table or generate a new one, but this is also quite simple, as we keep all transactions tables on disk. (Currently we have at least 50G of transactions tables and 200G of other customer data.)
We also let our customers access the summary tables directly with ODBC so that the advanced users can themselves experiment with the data.
We haven't had any problems handling this with quite modest Sun Ultra SPARCstation (2x200 Mhz). We recently upgraded one of our servers to a 2 CPU 400 Mhz UltraSPARC, and we are now planning to start handling transactions on the product level, which would mean a ten-fold increase of data. We think we can keep up with this by just adding more disk to our systems.
We are also experimenting with Intel-Linux to be able to get more CPU power cheaper. Now that we have the binary portable database format (new in Version 3.23), we will start to use this for some parts of the application.
Our initial feelings are that Linux will perform much better on low-to-medium load and Solaris will perform better when you start to get a high load because of extreme disk IO, but we don't yet have anything conclusive about this. After some discussion with a Linux Kernel developer, this might be a side effect of Linux giving so much resources to the batch job that the interactive performance gets very low. This makes the machine feel very slow and unresponsive while big batches are going. Hopefully this will be better handled in future Linux Kernels.
This should contain a technical description of the MySQL
benchmark suite (and crash-me), but that description is not
written yet. Currently, you should look at the code and results in the
`sql-bench' directory in the distribution (and of course on the Web page
at http://www.mysql.com/information/crash-me.php and (normally found in
the `sql-bench' directory in the MySQL distribution)).
It is meant to be a benchmark that will tell any user what things a given SQL implementation performs well or poorly at.
Note that this benchmark is single threaded, so it measures the minimum time for the operations.
For example, (run on the same NT 4.0 machine):
| Seconds | Seconds | |
| mysql | 367 | 249 |
| mysql_odbc | 464 | |
| db2_odbc | 1206 | |
| informix_odbc | 121126 | |
| ms-sql_odbc | 1634 | |
| oracle_odbc | 20800 | |
| solid_odbc | 877 | |
| sybase_odbc | 17614 |
| Seconds | Seconds | |
| mysql | 381 | 206 |
| mysql_odbc | 619 | |
| db2_odbc | 3460 | |
| informix_odbc | 2692 | |
| ms-sql_odbc | 4012 | |
| oracle_odbc | 11291 | |
| solid_odbc | 1801 | |
| sybase_odbc | 4802 |
In the above test MySQL was run with a 8M index cache.
Note that Oracle is not included because they asked to be removed. All Oracle benchmarks have to be passed by Oracle! We believe that makes Oracle benchmarks VERY biased because the above benchmarks are supposed to show what a standard installation can do for a single client.
crash-me tries to determine what features a database supports and
what it's capabilities and limitations are by actually running
queries. For example, it determines:
VARCHAR column can be
All MySQL clients that communicate with the server using the
mysqlclient library use the following environment variables:
| Name | Description |
MYSQL_UNIX_PORT | The default socket; used for connections to localhost
|
MYSQL_TCP_PORT | The default TCP/IP port |
MYSQL_PWD | The default password |
MYSQL_DEBUG | Debug-trace options when debugging |
TMPDIR | The directory where temporary tables/files are created |
Use of MYSQL_PWD is insecure.
See section 6.5 Connecting to the MySQL Server.
The `mysql' client uses the file named in the MYSQL_HISTFILE
environment variable to save the command-line history. The default value for
the history file is `$HOME/.mysql_history', where $HOME is the
value of the HOME environment variable. See section A Environment Variables.
All MySQL programs take many different options. However, every
MySQL program provides a --help option that you can use
to get a full description of the program's different options. For example, try
mysql --help.
You can override default options for all standard client programs with an option file. section 4.16.5 Option Files.
The list below briefly describes the MySQL programs:
myisamchk
myisamchk has many functions, it is described in its own
chapter. See section 15 Maintaining a MySQL Installation.
make_binary_distribution
support.mysql.com for the
convenience of other MySQL users.
msql2mysql
mSQL programs to MySQL. It doesn't
handle all cases, but it gives a good start when converting.
mysqlaccess
mysqladmin
mysqladmin can also be used to retrieve version,
process, and status information from the server.
See section 14.5 Administering a MySQL Server.
mysqlbug
mysqld
mysqldump
mysqlimport
LOAD DATA
INFILE. See section 14.7 Importing Data from Text Files.
mysqlshow
mysql_install_db
replace
msql2mysql, but that has more
general applicability as well. replace changes strings in place in
files or on the standard input. Uses a finite state machine to match longer
strings first. Can be used to swap strings. For example, this command
swaps a and b in the given files:
shell> replace a b b a -- file1 file2 ...
safe_mysqld is the recommended way to start a mysqld
daemon on Unix. safe_mysqld adds some safety features such as
restarting the server when an error occurs and logging run-time
information to a log file.
Normally one should never edit the safe_mysqld script, but
instead put the options to safe_mysqld in the
[safe_mysqld] section in the my.cnf
file. safe_mysqld will read all options from the [mysqld]
and [safe_mysqld] sections from the option files.
See section 4.16.5 Option Files.
Note that all options on the command line to safe_mysqld are passed
to mysqld. If you wants to use any options in safe_mysqld that
mysqld doesn't support, you must specify these in the option file.
Most of the options to safe_mysqld are the same as the options to
mysqld. See section 4.16.4 Command-line Options.
safe_mysqld supports the following options:
--basedir=path
--core-file-size=#
--defaults-extra-file=path
--defaults-file=path
--open-files=#
mysqld should be able to create. Passed to
ulimit -c.
--datadir=path
--err-log=path
--ledir=path
mysqld
--log=path
--no-defaults
--open-files=#
mysqld should be able to open. Passed to
ulimit -n.
--pid-file=path
--port=#
--socket=path
--timezone=#
TZ) variable to the value of this parameter.
--user=#
The safe_mysqld script is written so that it normally is able to start
a server that was installed from either a source or a binary version of
MySQL, even if these install the server in slightly different
locations. safe_mysqld expects one of these conditions to be true:
safe_mysqld is invoked. safe_mysqld looks under its working
directory for `bin' and `data' directories (for binary
distributions) or for `libexec' and `var' directories (for source
distributions). This condition should be met if you execute
safe_mysqld from your MySQL installation directory (for
example, `/usr/local/mysql' for a binary distribution).
safe_mysqld attempts to locate them by absolute pathnames. Typical
locations are `/usr/local/libexec' and `/usr/local/var'.
The actual locations are determined when the distribution was built from which
safe_mysqld comes. They should be correct if
MySQL was installed in a standard location.
Because safe_mysqld will try to find the server and databases relative
to its own working directory, you can install a binary distribution of
MySQL anywhere, as long as you start safe_mysqld from the
MySQL installation directory:
shell> cd mysql_installation_directory shell> bin/safe_mysqld &
If safe_mysqld fails, even when invoked from the MySQL
installation directory, you can modify it to use the path to mysqld
and the pathname options that are correct for your system. Note that if you
upgrade MySQL in the future, your modified version of
safe_mysqld will be overwritten, so you should make a copy of your
edited version that you can reinstall.
MySQL servers
mysqld_multi is meant for managing several mysqld
processes running in different UNIX sockets and TCP/IP ports.
The program will search for group(s) named [mysqld#] from my.cnf (or the
given --config-file=...), where # can be any positive number starting
from 1. These groups should be the same as the usual [mysqld]
group (e.g. options to mysqld, see MySQL manual for detailed
information about this group), but with those port, socket etc. options
that are wanted for each separate mysqld processes. The number in
the group name has another function; it can be used for starting,
stopping, or reporting some specific mysqld servers with this
program. See the usage and options below for more information.
Usage: mysqld_multi [OPTIONS] {start|stop|report} [GNR,GNR,GNR...]
or mysqld_multi [OPTIONS] {start|stop|report} [GNR-GNR,GNR,GNR-GNR,...]
The GNR above means the group number. You can start, stop or report any GNR, or several of them at the same time. (See --example) The GNRs list can be comma separated, or a dash combined, of which the latter means that all the GNRs between GNR1-GNR2 will be affected. Without GNR argument all the found groups will be either started, stopped, or reported. Note that you must not have any white spaces in the GNR list. Anything after a white space are ignored.
mysqld_multi supports the following options:
--config-file=...
[mysqld_multi]), but only groups
[mysqld#]. Without this option everything will be searched from the
ordinary my.cnf file.
--example
--help
--log=...
--mysqladmin=...
mysqladmin binary to be used for a server shutdown.
--mysqld=...
mysqld binary to be used. Note that you can give
safe_mysqld to this option also. The options are passed to
mysqld. Just make sure you have mysqld in your environment
variable PATH or fix safe_mysqld.
--no-log
--password=...
mysqladmin.
--tcp-ip
--user=...
mysqladmin.
--version
Some notes about mysqld_multi:
mysqld services (e.g using the mysqladmin) have the same
password and username for all the data directories accessed (to the
'mysql' database) And make sure that the user has the 'Shutdown_priv'
privilege! If you have many data- directories and many different 'mysql'
databases with different passwords for the MySQL 'root' user,
you may want to create a common 'multi_admin' user for each using the
same password (see below). Example how to do it:
shell> mysql -u root -S /tmp/mysql.sock -proot_password -e "GRANT SHUTDOWN ON *.* TO multi_admin@localhost IDENTIFIED BY 'multipass'" See section 6.8 How the Privilege System Works.You will have to do the above for each
mysqld running in each
data directory, that you have (just change the socket, -S=...)
pid-file is very important, if you are using safe_mysqld
to start mysqld (e.g. --mysqld=safe_mysqld) Every mysqld
should have it's own pid-file. The advantage using
safe_mysqld instead of mysqld directly here is, that
safe_mysqld 'guards' every mysqld process and will restart
it, if a mysqld process fails due to signal kill -9, or
similar. (Like segmentation fault, which MySQL should never do,
of course ;) Please note that safe_mysqld script may require that
you start it from a certain place. This means that you may have to CD to
a certain directory, before you start the mysqld_multi. If
you have problems starting, please see the safe_mysqld
script. Check especially the lines:
-------------------------------------------------------------------------- MY_PWD=`pwd` Check if we are starting this relative (for the binary release) if test -d /data/mysql -a -f ./share/mysql/english/errmsg.sys -a -x ./bin/mysqld -------------------------------------------------------------------------- See section 14.2 safe_mysqld, the wrapper around mysqld.The above test should be successful, or you may encounter problems.
mysqlds in the same data
directory. Use separate data directories, unless you KNOW what
you are doing!
mysqld.
mysqld group were intentionally left out from
the example. You may have 'gaps' in the config file. This gives you
more flexibility. The order in which the mysqlds are started or
stopped depends on the order in which they appear in the config file.
mysqld, but in order to
do this you need to be root when you start the mysqld_multi
script. Having the option in the config file doesn't matter; you will
just get a warning, if you are not the superuser and the mysqlds
are started under YOUR UNIX account. IMPORTANT: Make
sure that the pid-file and the data directory are
read+write(+execute for the latter one) accessible for THAT
UNIX user, who the specific mysqld process is started
as. DON'T use the UNIX root account for this, unless you
KNOW what you are doing!
mysqlds and why WOULD
YOU WANT to have separate mysqld processes. Starting multiple
mysqlds in one data directory WILL NOT give you extra
performance in a threaded system!
See section 21.6 Running Multiple MySQL Servers on the Same Machine.
This is an example of the config file on behalf of mysqld_multi.
# This file should probably be in your home dir (~/.my.cnf) or /etc/my.cnf # Version 2.1 by Jani Tolonen [mysqld_multi] mysqld = /usr/local/bin/safe_mysqld mysqladmin = /usr/local/bin/mysqladmin user = multi_admin password = multipass [mysqld2] socket = /tmp/mysql.sock2 port = 3307 pid-file = /usr/local/mysql/var2/hostname.pid2 datadir = /usr/local/mysql/var2 language = /usr/local/share/mysql/english user = john [mysqld3] socket = /tmp/mysql.sock3 port = 3308 pid-file = /usr/local/mysql/var3/hostname.pid3 datadir = /usr/local/mysql/var3 language = /usr/local/share/mysql/swedish user = monty [mysqld4] socket = /tmp/mysql.sock4 port = 3309 pid-file = /usr/local/mysql/var4/hostname.pid4 datadir = /usr/local/mysql/var4 language = /usr/local/share/mysql/estonia user = tonu [mysqld6] socket = /tmp/mysql.sock6 port = 3311 pid-file = /usr/local/mysql/var6/hostname.pid6 datadir = /usr/local/mysql/var6 language = /usr/local/share/mysql/japanese user = jani
See section 4.16.5 Option Files.
mysql is a simple SQL shell (with GNU readline capabilities).
It supports interactive and non-interactive use. When used interactively,
query results are presented in an ASCII-table format. When used
non-interactively (for example, as a filter), the result is presented in
tab-separated format. (The output format can be changed using command-line
options.) You can run scripts simply like this:
shell> mysql database < script.sql > output.tab
If you have problems due to insufficient memory in the client, use the
--quick option! This forces mysql to use
mysql_use_result() rather than mysql_store_result() to
retrieve the result set.
Using mysql is very easy. Just start it as follows:
mysql database or mysql --user=user_name --password=your_password database. Type a SQL statement, end it with `;', `\g', or `\G'
and press RETURN/ENTER.
mysql supports the following options:
-?, --help
-A, --no-auto-rehash
-B, --batch
--character-sets-dir=...
-C, --compress
-#, --debug[=...]
-D, --database=...
my.cnf file.
--default-character-set=...
-e, --execute=...
-E, --vertical
\G.
-f, --force
-g, --no-named-commands
-G, --enable-named-commands
-i, --ignore-space
-h, --host=...
-H, --html
-L, --skip-line-numbers
--no-pager
--no-tee
-n, --unbuffered
-N, --skip-column-names
-O, --set-variable var=option
--help lists variables.
-o, --one-database
--pager[=...]ENV variable PAGER. Valid
pagers are less, more, cat [> filename], etc. See interactive help (\h)
also. This option does not work in batch mode. Pager works only in UNIX.
-p[password], --password[=...]
-p you can't have a space between the option and the
password.
-P --port=...
-q, --quick
-r, --raw
--batch
-s, --silent
-S --socket=...
-t --table
-T, --debug-info
--tee=...
-u, --user=#
-U, --safe-updates[=#], --i-am-a-dummy[=#]
UPDATE and DELETE that uses keys. See below for
more information about this option. You can reset this option if you have
it in your my.cnf file by using --safe-updates=0.
-v, --verbose
-V, --version
-w, --wait
You can also set the following variables with -O or
--set-variable:
| Variablename | Default | Description |
| connect_timeout | 0 | Number of seconds before timeout connection. |
| max_allowed_packet | 16777216 | Max packetlength to send/receive from to server |
| net_buffer_length | 16384 | Buffer for TCP/IP and socket communication |
| select_limit | 1000 | Automatic limit for SELECT when using --i-am-a-dummy |
| max_join_size | 1000000 | Automatic limit for rows in a join when using --i-am-a-dummy. |
If you type 'help' on the command line, mysql will print out the
commands that it supports:
mysql> help MySQL commands: help (\h) Display this text. ? (\h) Synonym for `help'. clear (\c) Clear command. connect (\r) Reconnect to the server. Optional arguments are db and host. edit (\e) Edit command with $EDITOR. ego (\G) Send command to mysql server, display result vertically. exit (\q) Exit mysql. Same as quit. go (\g) Send command to mysql server. nopager (\n) Disable pager, print to stdout. notee (\t) Don't write into outfile. pager (\P) Set PAGER [to_pager]. Print the query results via PAGER. print (\p) Print current command. quit (\q) Quit mysql. rehash (\#) Rebuild completion hash. source (\.) Execute a SQL script file. Takes a file name as an argument. status (\s) Get status information from the server. tee (\T) Set outfile [to_outfile]. Append everything into given outfile. use (\u) Use another database. Takes database name as argument.
From the above, pager only works in UNIX.
The status command gives you some information about the
connection and the server you are using. If you are running in the
--safe-updates mode, status will also print the values for
the mysql variables that affect your queries.
A useful startup option for beginners (introduced in MySQL
Version 3.23.11) is --safe-mode (or --i-am-a-dummy for
users that has at some time done a DELETE FROM table_name but
forgot the WHERE clause. When using this option, mysql
sends the following command to the MySQL server when opening
the connection:
SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=#select_limit#,
SQL_MAX_JOIN_SIZE=#max_join_size#"
where #select_limit# and #max_join_size# are variables that
can be set from the mysql command line. See section 7.33 SET Syntax.
The effect of the above is:
UPDATE or DELETE statement
if you don't have a key constraint in the WHERE part. One can,
however, force an UPDATE/DELETE by using LIMIT:
UPDATE table_name SET not_key_column=# WHERE not_key_column=# LIMIT 1;
#select_limit# rows.
SELECT's that will probably need to examine more than
#max_join_size row combinations will be aborted.
Some useful hints about the mysql client:
Some data is much more readable when displayed vertically, instead of the usual horizontal box type output. For example longer text, which includes new lines, is often much easier to be read with vertical output.
mysql> select * from mails where length(txt) < 300 limit 300,1\G
*************************** 1. row ***************************
msg_nro: 3068
date: 2000-03-01 23:29:50
time_zone: +0200
mail_from: Monty
reply: monty@no.spam.com
mail_to: "Thimble Smith" <tim@no.spam.com>
sbj: UTF-8
txt: >>>>> "Thimble" == Thimble Smith writes:
Thimble> Hi. I think this is a good idea. Is anyone familiar with UTF-8
Thimble> or Unicode? Otherwise I'll put this on my TODO list and see what
Thimble> happens.
Yes, please do that.
Regards,
Monty
file: inbox-jani-1
hash: 190402944
1 row in set (0.09 sec)
tee option. The tee can be
started with option --tee=..., or from the command line
interactively with command tee. All the data displayed on the
screen will also be appended into a given file. This can be very useful
for debugging purposes also. The tee can be disabled from the
command line with command notee. Executing tee again
starts logging again. Without a parameter the previous file will be
used. Note that tee will flush the results into the file after
each command, just before the command line appears again waiting for the
next command.
--pager[=...]. Without argument, mysql client will look
for environment variable PAGER and set pager to that.
pager can be started from the interactive command line with
command pager and disabled with command nopager. The
command takes an argument optionally and the pager will be set to
that. Command pager can be called without an argument, but this
requires that the option --pager was used, or the pager
will default to stdout. pager works only in UNIX, since it uses
the popen() function, which doesn't exist in Windows. In Windows, the
tee option can be used instead, although it may not be as handy
as pager can be in some situations.
pager: You can use it to write to a file:
mysql> pager cat > /tmp/log.txtand the results will only go to a file. You can also pass any options for the programs that you want to use with the
pager:
mysql> pager less -n -i -SFrom the above do note the option '-S'. You may find it very useful when browsing the results; try the option with horizontal output (end commands with '\g', or ';') and with vertical output (end commands with '\G'). Sometimes a very wide result set is hard to be read from the screen, with option -S to less you can browse the results within the interactive less from left to right, preventing lines longer than your screen from being continued to the next line. This can make the result set much more readable. You can swith the mode between on and off within the interactive less with '-S'. See the 'h' for more help about less.
mysql> pager cat | tee /dr1/tmp/res.txt | tee /dr2/tmp/res2.txt | less -n -i -S
tee
enabled, pager set to 'less' and you will be able to browse the
results in unix 'less' and still have everything appended into a file
the same time. The difference between UNIX tee used with the
pager and the mysql client in-built tee, is that
the in-built tee works even if you don't have the UNIX tee
available. The in-built tee also logs everything that is printed
on the screen, where the UNIX tee used with pager doesn't
log quite that much. Last, but not least, the interactive tee is
more handy to switch on and off, when you want to log something into a
file, but want to be able to turn the feature off sometimes.
A utility for performing administrative operations. The syntax is:
shell> mysqladmin [OPTIONS] command [command-option] command ...
You can get a list of the options your version of mysqladmin supports
by executing mysqladmin --help.
The current mysqladmin supports the following commands:
| create databasename | Create a new database. |
| drop databasename | Delete a database and all its tables. |
| extended-status | Gives an extended status message from the server. |
| flush-hosts | Flush all cached hosts. |
| flush-logs | Flush all logs. |
| flush-tables | Flush all tables. |
| flush-privileges | Reload grant tables (same as reload). |
| kill id,id,... | Kill mysql threads. |
| password | New-password. Change old password to new-password. |
| ping | Check if mysqld is alive. |
| processlist | Show list of active threads in server. |
| reload | Reload grant tables. |
| refresh | Flush all tables and close and open logfiles. |
| shutdown | Take server down. |
| slave-start | Start slave replication thread. |
| slave-stop | Stop slave replication thread. |
| status | Gives a short status message from the server. |
| variables | Prints variables available. |
| version | Get version info from server. |
All commands can be shortened to their unique prefix. For example:
shell> mysqladmin proc stat +----+-------+-----------+----+-------------+------+-------+------+ | Id | User | Host | db | Command | Time | State | Info | +----+-------+-----------+----+-------------+------+-------+------+ | 6 | monty | localhost | | Processlist | 0 | | | +----+-------+-----------+----+-------------+------+-------+------+ Uptime: 10077 Threads: 1 Questions: 9 Slow queries: 0 Opens: 6 Flush tables: 1 Open tables: 2 Memory in use: 1092K Max memory used: 1116K
The mysqladmin status command result has the following columns:
| Uptime | Number of seconds the MySQL server has been up. |
| Threads | Number of active threads (clients). |
| Questions | Number of questions from clients since mysqld was started.
|
| Slow queries | Queries that have taken more than long_query_time seconds. See section 21.5 The Slow Query Log.
|
| Opens | How many tables mysqld has opened.
|
| Flush tables | Number of flush ..., refresh, and reload commands.
|
| Open tables | Number of tables that are open now. |
| Memory in use | Memory allocated directly by the mysqld code (only available when MySQL is compiled with --with-debug). |
| Max memory used | Maximum memory allocated directly by the mysqld code (only available when MySQL is compiled with --with-debug). |
If you do myslqadmin shutdown on a socket (in other words, on a
the computer where mysqld is running), mysqladmin will
wait until the MySQL pid-file is removed to ensure that
the mysqld server has stopped properly.
Utility to dump a database or a collection of database for backup or for transferring the data to another SQL server. The dump will contain SQL statements to create the table and/or populate the table:
shell> mysqldump [OPTIONS] database [tables] OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...] OR mysqldump [OPTIONS] --all-databases [OPTIONS]
If you don't give any tables or use the --databases or
--all-databases, the whole database(s) will be dumped.
You can get a list of the options your version of mysqldump supports
by executing mysqldump --help.
Note that if you run mysqldump without --quick or
--opt, mysqldump will load the whole result set into
memory before dumping the result. This will probably be a problem if
you are dumping a big database.
Note that if you are using a new copy of the mysqldump program
and you are going to do a dump that will be read into a very old MySQL
server, you should not use the --opt or -e options.
mysqldump supports the following options:
--add-locks
LOCK TABLES before and UNLOCK TABLE after each table dump.
(To get faster inserts into MySQL.)
--add-drop-table
drop table before each create statement.
-A, --all-databases
--databases with all
databases selected.
-a, --all
--allow-keywords
-c, --complete-insert
-C, --compress
-B, --databases
USE db_name; will be included in the output before each new database.
--delayed
INSERT DELAYED command.
-e, --extended-insert
INSERT syntax. (Gives more compact and
faster inserts statements.)
-#, --debug[=option_string]
--help
--fields-terminated-by=...
--fields-enclosed-by=...
--fields-optionally-enclosed-by=...
--fields-escaped-by=...
--lines-terminated-by=...
-T option and have the same
meaning as the corresponding clauses for LOAD DATA INFILE.
See section 7.23 LOAD DATA INFILE Syntax.
-F, --flush-logs
-f, --force,
-h, --host=..
localhost.
-l, --lock-tables.
READ LOCAL to allow concurrent inserts in the case of MyISAM
tables.
-n, --no-create-db
-t, --no-create-info
CREATE TABLE statement.)
-d, --no-data
--opt
--quick --add-drop-table --add-locks --extended-insert
--lock-tables. Should give you the fastest possible dump for reading
into a MySQL server.
-pyour_pass, --password[=your_pass]
mysqldump you will be prompted for a password.
-P port_num, --port=port_num
localhost, for which Unix sockets are
used.)
-q, --quick
mysql_use_result()
to do this.
-S /path/to/socket, --socket=/path/to/socket
localhost (which is the
default host).
--tables
-T, --tab=path-to-some-directory
table_name.sql file, that contains the SQL CREATE commands,
and a table_name.txt file, that contains the data, for each give table.
NOTE: This only works if mysqldump is run on the same
machine as the mysqld daemon. The format of the .txt file
is made according to the --fields-xxx and --lines--xxx options.
-u user_name, --user=user_name
-O var=option, --set-variable var=option
-v, --verbose
-V, --version
-w, --where='where-condition'
"--where=user='jimf'" "-wuserid>1" "-wuserid<1"
-O net_buffer_length=#, where # < 16M
--extended-insert or --opt), mysqldump will create
rows up to net_buffer_length length. If you increase this
variable, you should also ensure that the max_allowed_packet
variable in the MySQL server is bigger than the
net_buffer_length.
The most normal use of mysqldump is probably for making a backup of
whole databases. See section 21.2 Database Backups.
mysqldump --opt database > backup-file.sql
You can read this back into MySQL with:
mysql database < backup-file.sql
or
mysql -e "source /patch-to-backup/backup-file.sql" database
However, it's also very useful to populate another MySQL server with information from a database:
mysqldump --opt database | mysql --host=remote-host -C database
It is possible to dump several databases with one command:
mysqldump --databases database1 [database2 database3...] > my_databases.sql
If all the databases are wanted, one can use:
mysqldump --all-databases > all_databases.sql
mysqlimport provides a command-line interface to the LOAD DATA
INFILE SQL statement. Most options to mysqlimport correspond
directly to the same options to LOAD DATA INFILE.
See section 7.23 LOAD DATA INFILE Syntax.
mysqlimport is invoked like this:
shell> mysqlimport [options] database textfile1 [textfile2....]
For each text file named on the command line,
mysqlimport strips any extension from the filename and uses the result
to determine which table to import the file's contents into. For example,
files named `patient.txt', `patient.text', and `patient' would
all be imported into a table named patient.
mysqlimport supports the following options:
-c, --columns=...
LOAD DATA INFILE. See section 7.23 LOAD DATA INFILE Syntax.
-C, --compress
-#, --debug[=option_string]
-d, --delete
--fields-terminated-by=...
--fields-enclosed-by=...
--fields-optionally-enclosed-by=...
--fields-escaped-by=...
--lines-terminated-by=...
LOAD DATA INFILE. See section 7.23 LOAD DATA INFILE Syntax.
-f, --force
--force,
mysqlimport exits if a table doesn't exist.
--help
-h host_name, --host=host_name
localhost.
-i, --ignore
--replace option.
-l, --lock-tables
-L, --local
localhost (which is the default host).
-pyour_pass, --password[=your_pass]
mysqlimport you will be prompted for a password.
-P port_num, --port=port_num
localhost, for which Unix sockets are
used.)
-r, --replace
--replace and --ignore options control handling of input
records that duplicate existing records on unique key values. If you specify
--replace, new rows replace existing rows that have the same unique key
value. If you specify --ignore, input rows that duplicate an existing
row on a unique key value are skipped. If you don't specify either option, an
error occurs when a duplicate key value is found, and the rest of the text
file is ignored.
-s, --silent
-S /path/to/socket, --socket=/path/to/socket
localhost (which is the
default host).
-u user_name, --user=user_name
-v, --verbose
-V, --version
Here is a sample run using mysqlimport:
$ mysql --version mysql Ver 9.33 Distrib 3.22.25, for pc-linux-gnu (i686) $ uname -a Linux xxx.com 2.2.5-15 #1 Mon Apr 19 22:21:09 EDT 1999 i586 unknown $ mysql -e 'CREATE TABLE imptest(id INT, n VARCHAR(30))' test $ ed a 100 Max Sydow 101 Count Dracula . w imptest.txt 32 q $ od -c imptest.txt 0000000 1 0 0 \t M a x S y d o w \n 1 0 0000020 1 \t C o u n t D r a c u l a \n 0000040 $ mysqlimport --local test imptest.txt test.imptest: Records: 2 Deleted: 0 Skipped: 0 Warnings: 0 $ mysql -e 'SELECT * FROM imptest' test +------+---------------+ | id | n | +------+---------------+ | 100 | Max Sydow | | 101 | Count Dracula | +------+---------------+
perror can be used to print error message(s). perror can
be invoked like this:
shell> perror [OPTIONS] [ERRORCODE [ERRORCODE...]] For example: shell> perror 64 79 Error code 64: Machine is not on the network Error code 79: Can not access a needed shared library
perror can be used to display a description for a system error
code, or an MyISAM/ISAM table handler error code. The error messages
are mostly system dependent.
mysqlshow can be used to quickly look at which databases exist,
their tables, and the table's columns.
With the mysql program you can get the same information with the
SHOW commands. See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
mysqlshow is invoked like this:
shell> mysqlshow [OPTIONS] [database [table [column]]]
Note that in newer MySQL versions, you only see those database/tables/columns for which you have some privileges.
If the last argument contains a shell or SQL wild-card (*, ?,
% or _) then only what's matched by the wild card is shown.
This may cause some confusion when you try to display the columns for a
table with a _ as in this case mysqlshow only shows you
the table names that match the pattern. This is easily fixed by
adding an extra % last on the command line (as a separate
argument).
myisampack is used to compress MyISAM tables, and pack_isam
is used to compress ISAM tables. Because ISAM tables are deprecated, we
will only discuss myisampack here, but everything said about
myisampack should also be true for pack_isam.
myisampack works by compressing each column in the table separately.
The information needed to decompress columns is read into memory when the
table is opened. This results in much better performance when accessing
individual records, because you only have to uncompress exactly one record, not
a much larger disk block as when using Stacker on MS-DOS.
Usually, myisampack packs the data file 40%-70%.
MySQL uses memory mapping (mmap()) on compressed tables and
falls back to normal read/write file usage if mmap() doesn't work.
There are currently two limitations with myisampack:
myisampack can also pack BLOB or TEXT columns. The
older pack_isam could not do this.
Fixing these limitations is on our TODO list but with low priority.
myisampack is invoked like this:
shell> myisampack [options] filename ...
Each filename should be the name of an index (`.MYI') file. If you are not in the database directory, you should specify the pathname to the file. It is permissible to omit the `.MYI' extension.
myisampack supports the following options:
-b, --backup
tbl_name.OLD.
-#, --debug=debug_options
debug_options string often is
'd:t:o,filename'.
-f, --force
myisampack creates a temporary file named `tbl_name.TMD'
while it compresses the table. If you kill myisampack, the `.TMD'
file may not be deleted. Normally, myisampack exits with an error if
it finds that `tbl_name.TMD' exists. With --force,
myisampack packs the table anyway.
-?, --help
-j big_tbl_name, --join=big_tbl_name
big_tbl_name. All tables that are to be combined
MUST be identical (same column names and types, same indexes, etc.).
-p #, --packlength=#
myisampack stores all rows with length pointers of 1, 2, or 3
bytes. In most normal cases, myisampack can determine the right length
value before it begins packing the file, but it may notice during the packing
process that it could have used a shorter length. In this case,
myisampack will print a note that the next time you pack the same file,
you could use a shorter record length.)
-s, --silent
-t, --test
-T dir_name, --tmp_dir=dir_name
-v, --verbose
-V, --version
-w, --wait
mysqld server was
invoked with the --skip-locking option, it is not a good idea to
invoke myisampack if the table might be updated during the
packing process.
The sequence of commands shown below illustrates a typical table compression session:
shell> ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 53248 Apr 17 19:00 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-02-02 3:06:43 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafile pointer (bytes): 2 Keyfile pointer (bytes): 2 Max datafile length: 54657023 Max keyfile length: 33554431 Recordlength: 834 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip. text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 shell> myisampack station.MYI Compressing station.MYI: (1192 records) - Calculating statistics normal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space: 0 end-space: 12 table-lookups: 5 zero: 7 Original trees: 57 After join: 17 - Compressing file 87.14% shell> ls -l station.* -rw-rw-r-- 1 monty my 127874 Apr 17 19:00 station.MYD -rw-rw-r-- 1 monty my 55296 Apr 17 19:04 station.MYI -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> myisamchk -dvv station MyISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-04-17 19:04:26 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 1 Max datafile length: 16777215 Max keyfile length: 131071 Recordlength: 834 Record format: Compressed table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip. text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lookup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 always zero 2 9 21 336 4 always zero 2 9 22 340 1 3 9 23 341 8 table-lookup 9 0 24 349 8 table-lookup 10 0 25 357 8 always zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lookup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 always zero 2 9 34 392 4 table-lookup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 always zero 2 9 40 413 4 no zeros 2 9 41 417 4 always zero 2 9 42 421 4 no zeros 2 9 43 425 4 always zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9
The information printed by myisampack is described below:
normal
empty-space
empty-zero
empty-fill
INTEGER
column may be changed to MEDIUMINT).
pre-space
end-space
table-lookup
ENUM before Huffman compression.
zero
Original trees
After join
After a table has been compressed, myisamchk -dvv prints additional
information about each field:
Type
constant
no endspace
no endspace, not_always
no endspace, no empty
table-lookup
ENUM.
zerofill(n)
n bytes in the value are always 0 and are not
stored.
no zeros
always zero
Huff tree
Bits
After you have run pack_isam/myisampack you must run
isamchk/myisamchk to re-create the index. At this time you
can also sort the index blocks and create statistics needed for
the MySQL optimizer to work more efficiently:
myisamchk -rq --analyze --sort-index table_name.MYI isamchk -rq --analyze --sort-index table_name.ISM
After you have installed the packed table into the MySQL database
directory you should do mysqladmin flush-tables to force mysqld
to start using the new table.
myisamchk for Table Maintenance and Crash Recovery
Starting with MySQL Version 3.23.13, you can check MyISAM
tables with the CHECK TABLE command. See section 7.12 CHECK TABLE Syntax. You can
repair tables with the REPAIR TABLE command. See section 7.16 REPAIR TABLE Syntax.
To check/repair MyISAM tables (.MYI and .MYD) you should
use the myisamchk utility. To check/repair ISAM tables
(.ISM and .ISD) you should use the isamchk
utility. See section 8 MySQL Table Types.
In the following text we will talk about myisamchk, but everything
also applies to the old isamchk.
You can use the myisamchk utility to get information about your database
tables, check and repair them, or optimize them. The following sections
describe how to invoke myisamchk (including a description of its
options), how to set up a table maintenance schedule, and how to use
myisamchk to perform its various functions.
You can, in most cases, also use the command OPTIMIZE TABLES to
optimize and repair tables, but this is not as fast or reliable (in case
of real fatal errors) as myisamchk. On the other hand,
OPTIMIZE TABLE is easier to use and you don't have to worry about
flushing tables.
See section 7.11 OPTIMIZE TABLE Syntax.
myisamchk Invocation Syntax
myisamchk is invoked like this:
shell> myisamchk [options] tbl_name
The options specify what you want myisamchk to do. They are
described below. (You can also get a list of options by invoking
myisamchk --help.) With no options, myisamchk simply checks your
table. To get more information or to tell myisamchk to take corrective
action, specify options as described below and in the following sections.
tbl_name is the database table you want to check. If you run
myisamchk somewhere other than in the database directory, you must
specify the path to the file, because myisamchk has no idea where your
database is located. Actually, myisamchk doesn't care whether or not
the files you are working on are located in a database directory; you can
copy the files that correspond to a database table into another location and
perform recovery operations on them there.
You can name several tables on the myisamchk command line if you
wish. You can also specify a name as an index file
name (with the `.MYI' suffix), which allows you to specify all
tables in a directory by using the pattern `*.MYI'.
For example, if you are in a database directory, you can check all the
tables in the directory like this:
shell> myisamchk *.MYI
If you are not in the database directory, you can check all the tables there by specifying the path to the directory:
shell> myisamchk /path/to/database_dir/*.MYI
You can even check all tables in all databases by specifying a wild card with the path to the MySQL data directory:
shell> myisamchk /path/to/datadir/*/*.MYI
The recommended way to quickly check all tables is:
myisamchk --fast --silent /path/to/datadir/*/*.MYI isamchk --silent /path/to/datadir/*/*.ISM
myisamchk supports the following options.
Note that if you get an error like:
myisamchk: warning: 1 clients is using or hasn't closed the table properly
This means that you are trying to check a table that has been updated by the another program (like the mysqld server) that hasn't yet closed the file or that has died without closing the file properly.
If you mysqld is running, you must force a sync/close of all
tables with FLUSH TABLES and ensure that no one is using the
tables while you are running myisamchk. In MySQL Version 3.23 the easiest
way to avoid this problem is to use CHECK TABLE instead of
myisamchk to check tables.
myisamchk-# or --debug=debug_options
debug_options string often is
'd:t:o,filename'.
-? or --help
-O var=option, --set-variable var=option
myisamchk --help:
| key_buffer_size | 523264 |
| read_buffer_size | 262136 |
| write_buffer_size | 262136 |
| sort_buffer_size | 2097144 |
| sort_key_blocks | 16 |
| decode_bits | 9 |
key_buffer_size is only used when you check the table with -e or
repair it with -o.
sort_buffer_size is used when you repair the table with -r.
If you want a faster repair, set the above variables to about 1/4 of your
available memory. You can set both variables to big values, as only one
of the above buffers will be used at a time.
-s or --silent
-s
twice (-ss) to make myisamchk very silent.
-v or --verbose
-d and
-e. Use -v multiple times (-vv, -vvv) for more
verbosity!
-V or --version
myisamchk version and exit.
-w or, --wait
mysqld
on the table with --skip-locking, the table can only be locked
by another myisamchk command.
myisamchk-c or --check
myisamchk any options that override this.
-e or --extend-check
myisamchk or myisamchk --medium-check should, in most
cases, be able to find out if there are any errors in the table.
If you are using --extended-check and have much memory, you should
increase the value of key_buffer_size a lot!
-F or --fast
-C or --check-only-changed
-f or --force
myisamchk with -r (repair) on the table, if
myisamchk finds any errors in the table.
-i or --information
-m or --medium-check
-U or --update-state
--check-only-changed option, but you shouldn't use this
option if the mysqld server is using the table and you are
running mysqld with --skip-locking.
-T or --read-only
myisamchk
to check a table that is in use by some other application that doesn't
use locking (like mysqld --skip-locking).
The following options are used if you start myisamchk with
-r or -o:
-D # or --data-file-length=#
-e or --extend-check
-f or --force
table_name.TMD) instead of aborting.
-k # or keys-used=#
# indexes. If you are using MyISAM, tells which keys
to use, where each binary bit stands for one key (first key is bit 0).
This can be used to get faster inserts! Deactivated indexes can be
reactivated by using myisamchk -r. keys.
-l or --no-symlinks
myisamchk repairs the
table a symlink points at.
-r or --recover
-r, you
should then try -o. (Note that in the unlikely case that -r
fails, the data file is still intact.)
If you have lots of memory, you should increase the size of
sort_buffer_size!
-o or --safe-recover
-r, but can handle a couple of very unlikely cases that
-r cannot handle. This recovery method also uses much less disk
space than -r. Normally one should always first repair with
-r, and only if this fails use -o.
If you have lots of memory, you should increase the size of
key_buffer_size!
--character-sets-dir=...
--set-character-set=name
.t or --tmpdir=path
myisamchk will
use the environment variable TMPDIR for this.
-q or --quick
-q to force myisamchk to modify the original datafile in case
of duplicate keys
-u or --unpack
myisamchk
Other actions that myisamchk can do, besides repair and check tables:
-a or --analyze
myisamchk --describe --verbose table_name' or using SHOW KEYS in
MySQL.
-d or --description
-A or --set-auto-increment[=value]
-S or --sort-index
-R or --sort-records=#
SELECT and ORDER BY operations on
this index. (It may be VERY slow to do a sort the first time!)
To find out a table's index numbers, use SHOW INDEX, which shows a
table's indexes in the same order that myisamchk sees them. Indexes are
numbered beginning with 1.
myisamchk Memory Usage
Memory allocation is important when you run myisamchk.
myisamchk uses no more memory than you specify with the -O
options. If you are going to use myisamchk on very large files,
you should first decide how much memory you want it to use. The default
is to use only about 3M to fix things. By using larger values, you can
get myisamchk to operate faster. For example, if you have more
than 32M RAM, you could use options such as these (in addition to any
other options you might specify):
shell> myisamchk -O sort=16M -O key=16M -O read=1M -O write=1M ...
Using -O sort=16M should probably be enough for most cases.
Be aware that myisamchk uses temporary files in TMPDIR. If
TMPDIR points to a memory file system, you may easily get out of
memory errors. If this happens, set TMPDIR to point at some directory
with more space and restart myisamchk.
When repairing, myisamchk will also nead a lot of disk space:
--quick, as in this
case only the index file will be re-created. This space is needed on the
same disk as the original record file!
--repair (but not when using --safe-repair, you
will need space for a sort buffer for:
(largest_key + row_pointer_length)*number_of_rows * 2.
You can check the length of the keys and the row_pointer_length with
myisamchk -dv table.
This space is allocated on the temporary disk (specified by TMPDIR or
--tmpdir=#).
If you have a problem with disk space during repair, you can try to use
--safe-repair instead of --repair.
Starting with MySQL Version 3.23.13, you can check MyISAM
tables with the CHECK TABLE command. See section 7.12 CHECK TABLE Syntax. You can
repair tables with the REPAIR TABLE command. See section 7.16 REPAIR TABLE Syntax.
It is a good idea to perform table checks on a regular basis rather than
waiting for problems to occur. For maintenance purposes, you can use
myisamchk -s to check tables. The -s option (short for
--silent) causes myisamchk to run in silent mode, printing
messages only when errors occur.
It's also a good idea to check tables when the server starts up.
For example, whenever the machine has done a reboot in the middle of an
update, you usually need to check all the tables that could have been
affected. (This is an ``expected crashed table''.) You could add a test to
safe_mysqld that runs myisamchk to check all tables that have
been modified during the last 24 hours if there is an old `.pid'
(process ID) file left after a reboot. (The `.pid' file is created by
mysqld when it starts up and removed when it terminates normally. The
presence of a `.pid' file at system startup time indicates that
mysqld terminated abnormally.)
An even better test would be to check any table whose last-modified time is more recent than that of the `.pid' file.
You should also check your tables regularly during normal system
operation. At MySQL AB, we run a cron job to check all our important
tables once a week, using a line like this in a `crontab' file:
35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI
This prints out information about crashed tables so we can examine and repair them when needed.
As we haven't had any unexpectedly crashed tables (tables that become corrupted for reasons other than hardware trouble) for a couple of years now (this is really true), once a week is more than enough for us.
We recommend that to start with, you execute myisamchk -s each
night on all tables that have been updated during the last 24 hours,
until you come to trust MySQL as much as we do.
Normally you don't need to maintain MySQL tables that much. If you are
changing tables with dynamic size rows (tables with VARCHAR,
BLOB or TEXT columns) or have tables with many deleted rows
you may want to from time to time (once a month?) defragment/reclaim space
from the tables.
You can do this by using OPTIMIZE TABLE on the tables in question or
if you can take the mysqld server down for a while do:
isamchk -r --silent --sort-index -O sort_buffer_size=16M */*.ISM myisamchk -r --silent --sort-index -O sort_buffer_size=16M */*.MYI
To get a description of a table or statistics about it, use the commands shown below. We explain some of the information in more detail later:
myisamchk -d tbl_name
myisamchk in ``describe mode'' to produce a description of
your table. If you start the MySQL server using the
--skip-locking option, myisamchk may report an error for a
table that is updated while it runs. However, because myisamchk
doesn't change the table in describe mode, there isn't any risk of
destroying data.
myisamchk -d -v tbl_name
myisamchk is doing, add -v
to tell it to run in verbose mode.
myisamchk -eis tbl_name
myisamchk -eiv tbl_name
-eis, but tells you what is being done.
Example of myisamchk -d output:
MyISAM file: company.MYI
Record format: Fixed length
Data records: 1403698 Deleted blocks: 0
Recordlength: 226
table description:
Key Start Len Index Type
1 2 8 unique double
2 15 10 multip. text packed stripped
3 219 8 multip. double
4 63 10 multip. text packed stripped
5 167 2 multip. unsigned short
6 177 4 multip. unsigned long
7 155 4 multip. text
8 138 4 multip. unsigned long
9 177 4 multip. unsigned long
193 1 text
Example of myisamchk -d -v output:
MyISAM file: company
Record format: Fixed length
File-version: 1
Creation time: 1999-10-30 12:12:51
Recover time: 1999-10-31 19:13:01
Status: checked
Data records: 1403698 Deleted blocks: 0
Datafile parts: 1403698 Deleted data: 0
Datafilepointer (bytes): 3 Keyfile pointer (bytes): 3
Max datafile length: 3791650815 Max keyfile length: 4294967294
Recordlength: 226
table description:
Key Start Len Index Type Rec/key Root Blocksize
1 2 8 unique double 1 15845376 1024
2 15 10 multip. text packed stripped 2 25062400 1024
3 219 8 multip. double 73 40907776 1024
4 63 10 multip. text packed stripped 5 48097280 1024
5 167 2 multip. unsigned short 4840 55200768 1024
6 177 4 multip. unsigned long 1346 65145856 1024
7 155 4 multip. text 4995 75090944 1024
8 138 4 multip. unsigned long 87 85036032 1024
9 177 4 multip. unsigned long 178 96481280 1024
193 1 text
Example of myisamchk -eis output:
Checking MyISAM file: company Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 98% Packed: 17% Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1626.51, System time 232.36 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 627, Swaps 0 Blocks in 0 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 639, Involuntary context switches 28966
Example of myisamchk -eiv output:
Checking MyISAM file: company Data records: 1403698 Deleted blocks: 0 - check file-size - check delete-chain block_size 1024: index 1: index 2: index 3: index 4: index 5: index 6: index 7: index 8: index 9: No recordlinks - check index reference - check data record references index: 1 Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 2 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 - check data record references index: 3 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 - check data record references index: 5 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 6 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 7 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 8 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 9 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 9% Packed: 17% - check records and index references [LOTS OF ROW NUMBERS DELETED] Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Record blocks: 1403698 Delete blocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1639.63, System time 251.61 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0 Blocks in 4 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 10604, Involuntary context switches 122798
Here are the sizes of the data and index files for the table used in the preceding examples:
-rw-rw-r-- 1 monty tcx 317235748 Jan 12 17:30 company.MYD -rw-rw-r-- 1 davida tcx 96482304 Jan 12 18:35 company.MYM
Explanations for the types of information myisamchk produces are
given below. The ``keyfile'' is the index file. ``Record'' and ``row''
are synonymous:
ISAM file
Isam-version
Creation time
Recover time
Data records
Deleted blocks
Datafile: Parts
Data
records.
Deleted data
Datafile pointer
Keyfile pointer
Max datafile length
.MYD file) can become, in bytes.
Max keyfile length
.MYI file) can become, in bytes.
Recordlength
Record format
Fixed length.
Other possible values are Compressed and Packed.
table description
Key
Start
Len
Index
unique or multip. (multiple). Indicates whether or not one value
can exist multiple times in this index.
Type
packed, stripped or empty.
Root
Blocksize
Rec/key
myisamchk -a. If this is not updated at all, a default
value of 30 is given.
Keyblocks used
myisamchk, the values are very
high (very near the theoretical maximum).
Packed
CHAR/VARCHAR/DECIMAL keys. For long strings like
names, this can significantly reduce the space used. In the third example
above, the 4th key is 10 characters long and a 60% reduction in space is
achieved.
Max levels
Records
M.recordlength
Packed
Packed
value indicates the percentage of savings achieved by doing this.
Recordspace used
Empty space
Blocks/Record
myisamchk.
See section 15.4.3 Table Optimization.
Recordblocks
Deleteblocks
Recorddata
Deleted data
Lost space
Linkdata
Linkdata is the sum of the amount of
storage used by all such pointers.
If a table has been compressed with myisampack, myisamchk
-d prints additional information about each table column. See
section 14.10 The MySQL Compressed Read-only Table Generator, for an example of this
information and a description of what it means.
myisamchk for Crash Recovery
If you run mysqld with --skip-locking (which is the default on
some systems, like Linux), you can't reliably use myisamchk to
check a table when mysqld is using the same table. If you
can be sure that no one is accessing the tables through mysqld
while you run myisamchk, you only have to do mysqladmin
flush-tables before you start checking the tables. If you can't
guarantee the above, then you must take down mysqld while you
check the tables. If you run myisamchk while mysqld is updating
the tables, you may get a warning that a table is corrupt even if it
isn't.
If you are not using --skip-locking, you can use myisamchk
to check tables at any time. While you do this, all clients that try
to update the table will wait until myisamchk is ready before
continuing.
If you use myisamchk to repair or optimize tables, you
MUST always ensure that the mysqld server is not using
the table (this also applies if you are using --skip-locking).
If you don't take down mysqld you should at least do a
mysqladmin flush-tables before you run myisamchk.
The file format that MySQL uses to store data has been extensively tested, but there are always external circumstances that may cause database tables to become corrupted:
mysqld process being killed in the middle of a write.
This chapter describes how to check for and deal with data corruption in MySQL databases. If your tables get corrupted a lot you should try to find the reason for this! See section H.1 Debugging a MySQL server.
When performing crash recovery, it is important to understand that each table
tbl_name in a database corresponds to three files in the database
directory:
| File | Purpose |
| `tbl_name.frm' | Table definition (form) file |
| `tbl_name.MYD' | Data file |
| `tbl_name.MYI' | Index file |
Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files.
myisamchk works by creating a copy of the `.MYD' (data) file
row by row. It ends the repair stage by removing the old `.MYD'
file and renaming the new file to the original file name. If you use
--quick, myisamchk does not create a temporary `.MYD'
file, but instead assumes that the `.MYD' file is correct and only
generates a new index file without touching the `.MYD' file. This
is safe, because myisamchk automatically detects if the
`.MYD' file is corrupt and aborts the repair in this case. You can
also give two --quick options to myisamchk. In this case,
myisamchk does not abort on some errors (like duplicate key) but
instead tries to resolve them by modifying the `.MYD'
file. Normally the use of two --quick options is useful only if
you have too little free disk space to perform a normal repair. In this
case you should at least make a backup before running myisamchk.
To check a MyISAM table, use the following commands:
myisamchk tbl_name
myisamchk without options or
with either the -s or --silent option.
myisamchk -m tbl_name
myisamchk -e tbl_name
-e means
``extended check''). It does a check-read of every key for each row to verify
that they indeed point to the correct row. This may take a LONG time on a
big table with many keys. myisamchk will normally stop after the first
error it finds. If you want to obtain more information, you can add the
--verbose (-v) option. This causes myisamchk to keep
going, up through a maximum of 20 errors. In normal usage, a simple
myisamchk (with no arguments other than the table name) is sufficient.
myisamchk -e -i tbl_name
-i option tells myisamchk to
print some informational statistics, too.
In the following section we only talk about using myisamchk on MyISAM
tables (extensions .MYI and .MYD). If you are using
ISAM tables (extensions .ISM and .ISD), you should use
isamchk instead.
The symptoms of a corrupted table include queries that abort unexpectedly and observable errors such as these:
In these cases, you must repair your tables. myisamchk
can usually detect and fix most things that go wrong.
The repair process involves up to four stages, described below. Before you
begin, you should cd to the database directory and check the
permissions of the table files. Make sure they are readable by the Unix user
that mysqld runs as (and to you, because you need to access the files
you are checking). If it turns out you need to modify files, they must also
be writable by you.
If you are using MySQL Version 3.23.16 and above, you can (and should) use the
CHECK and REPAIR commands to check and repair MyISAM
tables. See section 7.12 CHECK TABLE Syntax. See section 7.16 REPAIR TABLE Syntax.
The manual section about table maintenence includes the options to
isamchk/myisamchk. See section 15.1 Using myisamchk for Table Maintenance and Crash Recovery.
The following section is for the cases where the above command fails or
if you want to use the extended features that isamchk/myisamchk provides.
If you are going to repair a table from the command line, you must first
take down the mysqld server. Note that when you do
mysqladmin shutdown on a remote server, the mysqld server
will still be alive for a while after mysqladmin returns, until
all queries are stopped and all keys have been flushed to disk.
Stage 1: Checking your tables
Run myisamchk *.MYI or myisamchk -e *.MYI if you have
more time. Use the -s (silent) option to suppress unnecessary
information.
If the mysqld server is done you should use the --update option to tell
myisamchk to mark the table as 'checked'.
You have to repair only those tables for which myisamchk announces an
error. For such tables, proceed to Stage 2.
If you get weird errors when checking (such as out of
memory errors), or if myisamchk crashes, go to Stage 3.
Stage 2: Easy safe repair
NOTE: If you want repairing to go much faster, you should add: -O
sort_buffer=# -O key_buffer=# (where # is about 1/4 of the available
memory) to all isamchk/myisamchk commands.
First, try myisamchk -r -q tbl_name (-r -q means ``quick
recovery mode''). This will attempt to repair the index file without
touching the data file. If the data file contains everything that it
should and the delete links point at the correct locations within the
data file, this should work, and the table is fixed. Start repairing the
next table. Otherwise, use the following procedure:
myisamchk -r tbl_name (-r means ``recovery mode''). This will
remove incorrect records and deleted records from the data file and
reconstruct the index file.
myisamchk --safe-recover tbl_name.
Safe recovery mode uses an old recovery method that handles a few cases that
regular recovery mode doesn't (but is slower).
If you get weird errors when repairing (such as out of
memory errors), or if myisamchk crashes, go to Stage 3.
Stage 3: Difficult repair
You should only reach this stage if the first 16K block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it's necessary to create a new index file. Do so as follows:
shell> mysql db_name mysql> SET AUTOCOMMIT=1; mysql> TRUNCATE table_name; mysql> quitIf your SQL version doesn't have
TRUNCATE, use DELETE FROM
table_name instead.
Go back to Stage 2. myisamchk -r -q should work now. (This shouldn't
be an endless loop.)
Stage 4: Very difficult repair
You should reach this stage only if the description file has also crashed. That should never happen, because the description file isn't changed after the table is created:
myisamchk -r.
To coalesce fragmented records and eliminate wasted space resulting from
deleting or updating records, run myisamchk in recovery mode:
shell> myisamchk -r tbl_name
You can optimize a table in the same way using the SQL OPTIMIZE TABLE
statement. OPTIMIZE TABLE does a repair of the table, a key
analyzes and also sorts the index tree to give faster key lookups.
There is also no possibility of unwanted interaction between a utility
and the server, because the server does all the work when you use
OPTIMIZE TABLE. See section 7.11 OPTIMIZE TABLE Syntax.
myisamchk also has a number of other options you can use to improve
the performance of a table:
-S, --sort-index
-R index_num, --sort-records=index_num
-a, --analyze
For a full description of the option, see See section 15.1.1 myisamchk Invocation Syntax.
When using MySQL with log files, you will, from time to time, want to remove/backup old log files and tell MySQL to start logging on new files. See section 21.3 The Update Log.
On a Linux (Redhat) installation, you can use the
mysql-log-rotate script for this. If you installed MySQL
from an RPM distribution, the script should have been installed
automatically.
On other systems you must install a short script yourself that you
start from cron to handle log files.
You can force MySQL to start using new log files by using
mysqladmin flush-logs or by using the SQL command FLUSH LOGS.
If you are using MySQL Version 3.21 you must use mysqladmin refresh.
The above command does the following:
--log) or slow query logging
(--log-slow-queries) is used, closes and reopens the log file.
(`mysql.log' and ``hostname`-slow.log' as default).
--log-update) is used, closes the update log and
opens a new log file with a higher sequence number.
If you are using only an update log, you only have to flush the logs and then move away the old update log files to a backup. If you are using the normal logging, you can do something like:
shell> cd mysql-data-directory shell> mv mysql.log mysql.old shell> mysqladmin flush-logs
and then take a backup and remove `mysql.old'.
There are two ways to add new functions to MySQL:
CREATE FUNCTION and DROP FUNCTION statements.
See section 7.38 CREATE FUNCTION/DROP FUNCTION Syntax.
mysqld server and become
available on a permanent basis.
Each method has advantages and disadvantages:
Whichever method you use to add new functions, they may be used just like
native functions such as ABS() or SOUNDEX().
For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. The MySQL source distribution includes a file `sql/udf_example.cc' that defines 5 new functions. Consult this file to see how UDF calling conventions work.
For each function that you want to use in SQL statements, you should define
corresponding C (or C++) functions. In the discussion below, the name
``xxx'' is used for an example function name. To distinquish between SQL and
C/C++ usage, XXX() (uppercase) indicates a SQL function call, and
xxx() (lowercase) indicates a C/C++ function call.
The C/C++ functions that you write to implement the inferface for
XXX() are:
xxx() (required)
| SQL type | C/C++ type |
STRING | char *
|
INTEGER | long long
|
REAL | double
|
xxx_init() (optional)
xxx(). It can be used to:
XXX().
REAL functions) the maximum number of decimals.
NULL.
xxx_deinit() (optional)
xxx(). It should deallocate any
memory allocated by the initialization function.
When a SQL statement invokes XXX(), MySQL calls the
initialization function xxx_init() to let it perform any required
setup, such as argument checking or memory allocation. If xxx_init()
returns an error, the SQL statement is aborted with an error message and the
main and deinitialization functions are not called. Otherwise, the main
function xxx() is called once for each row. After all rows have been
processed, the deinitialization function xxx_deinit() is called so it
can perform any required cleanup.
All functions must be thread safe (not just the main function,
but the initialization and deinitialization functions as well). This means
that you are not allowed to allocate any global or static variables that
change! If you need memory, you should allocate it in xxx_init()
and free it in xxx_deinit().
The main function should be declared as shown below. Note that the return
type and parameters differ, depending on whether you will declare the SQL
function XXX() to return STRING, INTEGER, or REAL
in the CREATE FUNCTION statement:
For STRING functions:
char *xxx(UDF_INIT *initid, UDF_ARGS *args,
char *result, unsigned long *length,
char *is_null, char *error);
For INTEGER functions:
long long xxx(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
For REAL functions:
double xxx(UDF_INIT *initid, UDF_ARGS *args,
char *is_null, char *error);
The initialization and deinitialization functions are declared like this:
my_bool xxx_init(UDF_INIT *initid, UDF_ARGS *args, char *message); void xxx_deinit(UDF_INIT *initid);
The initid parameter is passed to all three functions. It points to a
UDF_INIT structure that is used to communicate information between
functions. The UDF_INIT structure members are listed below. The
initialization function should fill in any members that it wishes to change.
(To use the default for a member, leave it unchanged.):
my_bool maybe_null
xxx_init() should set maybe_null to 1 if xxx()
can return NULL. The default value is 1 if any of the
arguments are declared maybe_null.
unsigned int decimals
1.34, 1.345, and 1.3, the default would be 3,
because 1.345 has 3 decimals.
unsigned int max_length
initid->decimals. (For numeric functions, the length
includes any sign or decimal point characters.)
char *ptr
initid->ptr to communicate allocated memory
between functions. In xxx_init(), allocate the memory and assign it
to this pointer:
initid->ptr = allocated_memory;In
xxx() and xxx_deinit(), refer to initid->ptr to use
or deallocate the memory.
The args parameter points to a UDF_ARGS structure that thas the
members listed below:
unsigned int arg_count
if (args->arg_count != 2)
{
strcpy(message,"XXX() requires two arguments");
return 1;
}
enum Item_result *arg_type
STRING_RESULT, INT_RESULT, and REAL_RESULT.
To make sure that arguments are of a given type and return an
error if they are not, check the arg_type array in the initialization
function. For example:
if (args->arg_type[0] != STRING_RESULT ||
args->arg_type[1] != INT_RESULT)
{
strcpy(message,"XXX() requires a string and an integer");
return 1;
}
As an alternative to requiring your function's arguments to be of particular
types, you can use the initialization function to set the arg_type
elements to the types you want. This causes MySQL to coerce
arguments to those types for each call to xxx(). For example, to
specify coercion of the first two arguments to string and integer, do this in
xxx_init():
args->arg_type[0] = STRING_RESULT; args->arg_type[1] = INT_RESULT;
char **args
args->args communicates information to the initialization function
about the general nature of the arguments your function was called with. For a
constant argument i, args->args[i] points to the argument
value. (See below for instructions on how to access the value properly.)
For a non-constant argument, args->args[i] is 0.
A constant argument is an expression that uses only constants, such as
3 or 4*7-2 or SIN(3.14). A non-constant argument is an
expression that refers to values that may change from row to row, such as
column names or functions that are called with non-constant arguments.
For each invocation of the main function, args->args contains the
actual arguments that are passed for the row currently being processed.
Functions can refer to an argument i as follows:
STRING_RESULT is given as a string pointer plus a
length, to allow handling of binary data or data of arbitrary length. The
string contents are available as args->args[i] and the string length
is args->lengths[i]. You should not assume that strings are
null-terminated.
INT_RESULT, you must cast
args->args[i] to a long long value:
long long int_val; int_val = *((long long*) args->args[i]);
REAL_RESULT, you must cast
args->args[i] to a double value:
double real_val; real_val = *((double*) args->args[i]);
unsigned long *lengths
lengths array indicates the
maximum string length for each argument. For each invocation of the main
function, lengths contains the actual lengths of any string arguments
that are passed for the row currently being processed. For arguments of
types INT_RESULT or REAL_RESULT, lengths still contains
the maximum length of the argument (as for the initialization function).
The initialization function should return 0 if no error occurred and
1 otherwise. If an error occurs, xxx_init() should store a
null-terminated error message in the message parameter. The message
will be returned to the client. The message buffer is
MYSQL_ERRMSG_SIZE characters long, but you should try to keep the
message to less than 80 characters so that it fits the width of a standard
terminal screen.
The return value of the main function xxx() is the function value, for
long long and double functions. For string functions, the
string is returned in the result and length arguments.
result is a buffer at least 255 bytes long. Set these to the contents
and length of the return value. For example:
memcpy(result, "result string", 13); *length = 13;
The string function return value normally also points to the result.
To indicate a return value of NULL in the main function, set
is_null to 1:
*is_null = 1;
To indicate an error return in the main function, set the error
parameter to 1:
*error = 1;
If xxx() sets *error to 1 for any row, the function
value is NULL for the current row and for any subsequent rows
processed by the statement in which XXX() was invoked. (xxx()
will not even be called for subsequent rows.) NOTE: In
MySQL versions prior to 3.22.10, you should set both *error
and *is_null:
*error = 1; *is_null = 1;
Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF file `udf_example.cc' that is included in the MySQL source distribution. This file contains the following functions:
metaphon() returns a metaphon string of the string argument.
This is something like a soundex string, but it's more tuned for English.
myfunc_double() returns the sum of the ASCII values of the
characters in its arguments, divided by the sum of the length of its arguments.
myfunc_int() returns the sum of the length of its arguments.
lookup() returns the IP number for a hostname.
reverse_lookup() returns the hostname for an IP number.
The function may be called with a string "xxx.xxx.xxx.xxx" or
four numbers.
A dynamically loadable file should be compiled as a sharable object file, using a command something like this:
shell> gcc -shared -o udf_example.so myfunc.cc
You can easily find out the correct compiler options for your system by running this command in the `sql' directory of your MySQL source tree:
shell> make udf_example.o
You should run a compile command similar to the one that make displays,
except that you should remove the -c option near the end of the line
and add -o udf_example.so to the end of the line. (On some systems,
you may need to leave the -c on the command.)
Once you compile a shared object containing UDFs, you must install it
and tell MySQL about it. Compiling a shared object from
`udf_example.cc' produces a file named something like
`udf_example.so' (the exact name may vary from platform to platform).
Copy this file to some directory searched by ld, such as
`/usr/lib'. On many systems, you can set the LD_LIBRARY or
LD_LIBRARY_PATH environment variable to point at the directory where
you have your UDF function files. The dlopen manual page tells you
which variable you should use on your system. You should set this in
mysql.server or safe_mysqld and restart mysqld.
After the library is installed, notify mysqld about the new
functions with these commands:
mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so";
Functions can be deleted using DROP FUNCTION:
mysql> DROP FUNCTION metaphon; mysql> DROP FUNCTION myfunc_double; mysql> DROP FUNCTION myfunc_int; mysql> DROP FUNCTION lookup; mysql> DROP FUNCTION reverse_lookup;
The CREATE FUNCTION and DROP FUNCTION statements update the
system table func in the mysql database. The function's name,
type and shared library name are saved in the table. You must have the
insert and delete privileges for the mysql database
to create and drop functions.
You should not use CREATE FUNCTION to add a function that has already
been created. If you need to reinstall a function, you should remove it with
DROP FUNCTION and then reinstall it with CREATE FUNCTION. You
would need to do this, for example, if you recompile a new version of your
function, so that mysqld gets the new version. Otherwise the server
will continue to use the old version.
Active functions are reloaded each time the server starts, unless you start
mysqld with the --skip-grant-tables option. In this case, UDF
initialization is skipped and UDFs are unavailable. (An active function is
one that has been loaded with CREATE FUNCTION and not removed with
DROP FUNCTION.)
The procedure for adding a new native function is described below. Note that you cannot add native functions to a binary distribution because the procedure involves modifying MySQL source code. You must compile MySQL yourself from a source distribution. Also note that if you migrate to another version of MySQL (for example, when a new version is released), you will need to repeat the procedure with the new version.
To add a new native MySQL function, follow these steps:
sql_functions[] array.
yacc should define (this should be added at the
beginning of the file). Then define the function parameters and add an
``item'' with these parameters to the simple_expr parsing rule.
For an example, check all occurrences of SOUNDEX in
`sql_yacc.yy' to see how this is done.
Item_num_func or
Item_str_func, depending on whether your function returns a number or a
string.
double Item_func_newname::val() longlong Item_func_newname::val_int() String *Item_func_newname::Str(String *str)
void Item_func_newname::fix_length_and_dec()This function should at least calculate
max_length based on the
given arguments. max_length is the maximum number of characters
the function may return. This function should also set maybe_null = 0
if the main function can't return a NULL value. The function can check
if any of the function arguments can return NULL by checking the
arguments maybe_null variable.
All functions must be thread safe.
For string functions, there are some additional considerations to be aware of:
String *str argument provides a string
buffer that may be used to hold the result.
In MySQL, you can define a procedure in C++ that can access and
modify the data in a query before it is sent to the client. The modification
can be done on row-by-row or GROUP BY level.
We have created an example procedure in MySQL Version 3.23 to show you what can be done.
analyse([max elements,[max memory]])
This procedure is defined in the `sql/sql_analyse.cc'. This examines the result from your query and returns an analysis of the results:
max elements (default 256) is the maximum number of distinct values
analyse will notice per column. This is used by analyse to check if
the optimal column type should be of type ENUM.
max memory (default 8192) is the maximum memory analyse should
allocate per column while trying to find all distinct values.
SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])
For the moment, the only documentation for this is the source.
You can find all information about procedures by examining the following files:
MySQL provides support for ODBC by means of the MyODBC program.
MyODBC is a 32-bit ODBC (2.50) level 0 (with level 1 and level 2 features) driver for connecting an ODBC-aware application to MySQL. MyODBC works on Windows95, Windows98, NT, and on most Unix platforms.
Normally you only need to install MyODBC on Windows machines. You only need MyODBC for Unix if you have a program like ColdFusion that is running on the Unix machine and uses ODBC to connect to the databases.
MyODBC is in public domain, and you can find the newest version at http://www.mysql.com/downloads/api-myodbc.html.
If you want to install MyODBC on a Unix box, you will also need an ODBC manager. MyODBC is known to work with most of the Unix ODBC managers. You can find a list at these in the ODBC-related links section on the MySQL useful links page. See section 1.9 Useful MySQL-related Links.
On Windows/NT you may get the following error when trying to install MyODBC:
An error occurred while copying C:\WINDOWS\SYSTEM\MFC30.DLL. Restart Windows and try installing again (before running any applications which use ODBC)
The problem in this case is that some other program is using ODBC and because of how Windows is designed, you cannot in this case install new ODBC drivers with Microsoft's ODBC setup program. The solution to this is to reboot your computer in ``safe mode`` (Choose this by pressing F8 just before your machine starts Windows during rebooting), install MyODBC, and reboot to normal mode:
GRANT
command. See section 7.34 GRANT and REVOKE Syntax.
Notice that there are other configuration options on the screen of MySQL (trace, don't prompt on connect, etc) that you can try if you run into problems.
There are three possibilities for specifying the server name on Windows95:
ip hostnameFor example:
194.216.84.21 my_hostname
Example of how to fill in the ODBC setup:
Windows DSN name: test Description: This is my test database MySql Database: test Server: 194.216.84.21 User: monty Password: my_password Port:
The value for the Windows DSN name field is any name that is unique
in your Windows ODBC setup.
You don't have to specify values for the Server, User,
Password, or Port fields in the ODBC setup screen.
However, if you do, the values will be used as the defaults later when
you attempt to make a connection. You have the option of changing the
values at that time.
If the port number is not given, the default port (3306) is used.
If you specify the option Read options from C:\my.cnf, the groups
client and odbc will be read from the `C:\my.cnf' file.
You can use all options that are usable by mysql_options().
See section 22.4.38 mysql_options().
MyODBC has been tested with Access, Admndemo.exe, C++-Builder, Borland Builder 4, Centura Team Developer (formerly Gupta SQL/Windows), ColdFusion (on Solaris and NT with svc pack 5), Crystal Reports, DataJunction, Delphi, ERwin, Excel, iHTML, FileMaker Pro, FoxPro, Notes 4.5/4.6, SBSS, Perl DBD-ODBC, Paradox, Powerbuilder, Powerdesigner 32 bit, VC++, and Visual Basic.
If you know of any other applications that work with MyODBC, please send mail to myodbc@lists.mysql.com about this!
With some programs you may get an error like:
Another user has modifies the record that you have modified. In most
cases this can be solved by doing one of the following things:
If the above doesn't help, you should do a MyODBC trace file and
try to figure out why things go wrong.
Most programs should work with MyODBC, but for each of those listed below, we have tested it ourselves or received confirmation from some user that it works:
Microsoft Data Access Components) from
http://www.microsoft.com/data. This will fix the following bug in Access: when you export data to MySQL, the table and column names
aren't specified. Another way to around this bug is to upgrade to
MyODBC Version 2.50.33 and MySQL Version 3.23.x, which together provide a
workaround for this bug!
Note that if you are using MySQL Version 3.22, you must to apply the
MDAC patch and use MyODBC 2.50.32 or 2.50.34 and above to go around
this problem.
#Deleted#.
TIMESTAMP(14) or simple TIMESTAMP
is recommended instead of other TIMESTAMP(X) variations.
#Deleted#
or that you can't find or update rows.
Another user has changed your data after
adding a TIMESTAMP column, the following trick may help you:
Don't use table data sheet view. Create instead a form with the
fields you want, and use that form data sheet view. You should
set the DefaultValue property for the TIMESTAMP column to
NOW(). It may be a good idea to hide the TIMESTAMP column
from view so your users are not confused.
BLOB columns as OLE OBJECTS. If
you want to have MEMO columns instead, you should change the
column to TEXT with ALTER TABLE.
DATE columns properly. If you have a problem
with these, change the columns to DATETIME.
"Query|SQLSpecific|Pass-Through" from the Access menu.
TINYINT instead of TINYINT UNSIGNED. This will give you
problems if you have values > 127 in the column!
CursorLocation
Property as adUseServer will return for the RecordCount
Property a result of -1. To have the right value, you need to set this
property to adUseClient, like is showing in the VB code below:
Dim myconn As New ADODB.Connection Dim myrs As New Recordset Dim mySQL As String Dim myrows As Long myconn.Open "DSN=MyODBCsample" mySQL = "SELECT * from user" myrs.Source = mySQL Set myrs.ActiveConnection = myconn myrs.CursorLocation = adUseClient myrs.Open myrows = myrs.RecordCount myrs.Close myconn.CloseAnother workaround is to use a
SELECT COUNT(*) statement
for a similar query to get the correct row count.
Active or use the
method Open. Note that Active will start by automatically
issuing a SELECT * FROM ... query that may not be a good thing if
your tables are big!
VARCHAR rather than ENUM, as
it exports the latter in a manner that causes MySQL grief.
CONCAT() function. For example:
select CONCAT(rise_time), CONCAT(set_time)
from sunrise_sunset;
Values retrieved as strings this way should be correctly recognized
as time values by Excel97.
The purpose of CONCAT() in this example is to fool ODBC into thinking
the column is of ``string type''. Without the CONCAT(), ODBC knows the
column is of time type, and Excel does not understand that.
Note that this is a bug in Excel, because it automatically converts a
string to a time. This would be great if the source was a text file, but
is plain stupid when the source is an ODBC connection that reports
exact types for each column.
MyODBC driver and the Add-in Microsoft Query help.
For example, create a db with a table containing 2 columns of text:
fReg:= TRegistry.Create;
fReg.OpenKey('\Software\ODBC\ODBC.INI\DocumentsFab', True);
fReg.WriteString('Database', 'Documents');
fReg.WriteString('Description', ' ');
fReg.WriteString('Driver', 'C:\WINNT\System32\myodbc.dll');
fReg.WriteString('Flag', '1');
fReg.WriteString('Password', '');
fReg.WriteString('Port', ' ');
fReg.WriteString('Server', 'xmark');
fReg.WriteString('User', 'winuser');
fReg.OpenKey('\Software\ODBC\ODBC.INI\ODBC Data Sources', True);
fReg.WriteString('DocumentsFab', 'MySQL');
fReg.CloseKey;
fReg.Free;
Memo1.Lines.Add('DATABASE NAME=');
Memo1.Lines.Add('USER NAME=');
Memo1.Lines.Add('ODBC DSN=DocumentsFab');
Memo1.Lines.Add('OPEN MODE=READ/WRITE');
Memo1.Lines.Add('BATCH COUNT=200');
Memo1.Lines.Add('LANGDRIVER=');
Memo1.Lines.Add('MAX ROWS=-1');
Memo1.Lines.Add('SCHEMA CACHE DIR=');
Memo1.Lines.Add('SCHEMA CACHE SIZE=8');
Memo1.Lines.Add('SCHEMA CACHE TIME=-1');
Memo1.Lines.Add('SQLPASSTHRU MODE=SHARED AUTOCOMMIT');
Memo1.Lines.Add('SQLQRYMODE=');
Memo1.Lines.Add('ENABLE SCHEMA CACHE=FALSE');
Memo1.Lines.Add('ENABLE BCD=FALSE');
Memo1.Lines.Add('ROWSET SIZE=20');
Memo1.Lines.Add('BLOBS TO CACHE=64');
Memo1.Lines.Add('BLOB SIZE=32');
AliasEditor.Add('DocumentsFab','MySQL',Memo1.Lines);
SHOW PROCESSLIST will not work properly. The fix is to set
add the option OPTION=16834 in the ODBC connect string or set
the Change BIGINT columns to INT option in the MyODBC connect screen.
AUTO_INCREMENT Column in ODBC
A common problem is how to get the value of an automatically generated ID
from an INSERT. With ODBC, you can do something like this (assuming
that auto is an AUTO_INCREMENT field):
INSERT INTO foo (auto,text) VALUES(NULL,'text'); SELECT LAST_INSERT_ID();
Or, if you are just going to insert the ID into another table, you can do this:
INSERT INTO foo (auto,text) VALUES(NULL,'text'); INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text');
For the benefit of some ODBC applications (at least Delphi and Access), the following query can be used to find a newly inserted row:
SELECT * FROM tbl_name WHERE auto IS NULL;
If you encounter difficulties with MyODBC, you should start by
making a log file from the ODBC manager (the log you get when requesting
logs from ODBCADMIN) and a MyODBC log. To get a MyODBC
log, tag the `Trace MyODBC' option flag in the MyODBC
connect/configure screen. The log will be written to file
`C:\myodbc.log'. Note that you must use MYSQL.DLL and not
MYSQL2.DLL for this option to work!
Check the queries that MyODBC sends to the MySQL server. You
should be able to find this by searching after the string
>mysql_real_query in the `myodbc.log' file.
You should also try duplicating the queries in the mysql monitor
or admndemo to find out if the error is MyODBC or MySQL.
If you find out something is wrong, please only send the relevant rows (max 40 rows) to myodbc@lists.mysql.com. Please never send the whole MyODBC or ODBC log file!
If you are unable to find out what's wrong, the last option is to make an archive (tar or zip) that contains a MyODBC log file, the ODBC log file, and a README file that explains the problem. You can send this to ftp://support.mysql.com/pub/mysql/secret. Only we at MySQL AB will have access to the files you upload, and we will be very discrete with the data!
If you can create a program that also shows this problem, please upload this too!
If the program works with some other SQL server, you should make an ODBC log file where you do exactly the same thing in the other SQL server.
Remember that the more information you can supply to us, the more likely it is that we can fix the problem!
The contrib section includes programs that let you authenticate your users from a MySQL database and also let you log your log files into a MySQL table. See section C Contributed Programs.
You can change the Apache logging format to be easily readable by MySQL by putting the following into the Apache configuration file:
LogFormat \
"\"%h\",%{%Y%m%d%H%M%S}t,%>s,\"%b\",\"%{Content-Type}o\", \
\"%U\",\"%{Referer}i\",\"%{User-Agent}i\""
In MySQL you can do something like this:
LOAD DATA INFILE '/local/access_log' INTO TABLE table_name FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' ESCAPED BY '\\'
When you run into problems, the first thing you should do is to find out which program / piece of equipment is causing problems:
kbd_mode -a on it.
top, ps, taskmanager, or some similar program,
to check which program is taking all CPU or is locking the machine.
top, df, or a similar program if you are out of
memory, disk space, open files, or some other critical resource.
If after you have examined all other possibilities and you have concluded that it's the MySQL server or a MySQL client that is causing the problem, it's time to do a bug report for our mailing list or our support team. In the bug report, try to give a very detailed description of how the system is behaving and what you think is happening. You should also state why you think it's MySQL that is causing the problems. Take into consideration all the situations in this chapter. State any problems exactly how they appear when you examine your system. Use the 'cut and paste' method for any output and/or error messages from programs and/or log files!
Try to describe in detail which program is not working and all symptoms you see! We have in the past received many bug reports that just state "the system doesn't work". This doesn't provide us with any information about what could be the problem.
If a program fails, it's always useful to know:
top. Let the
program run for a while, it may be evaluating something heavy.
mysqld server that is causing problems, can you
do mysqladmin -u root ping or mysqladmin -u root processlist?
mysql, for example)
when you try to connect to the MySQL server?
Does the client jam? Do you get any output from the program?
When sending a bug report, you should of follow the outlines described in this manual. See section 2.2 Asking Questions or Reporting Bugs.
All MySQL versions are tested on many platforms before they are released. This doesn't mean that there aren't any bugs in MySQL, but it means if there are bugs, they are very few and can be hard to find. If you have a problem, it will always help if you try to find out exactly what crashes your system, as you will have a much better chance of getting this fixed quickly.
First, you should try to find out whether the problem is that the
mysqld daemon dies or whether your problem has to do with your
client. You can check how long your mysqld server has been up by
executing mysqladmin version. If mysqld has died, you may
find the reason for this in the file
`mysql-data-directory/'hostname'.err'.
Many crashes of MySQL are caused by corrupted index / data
files. MySQL will update the data on disk, with the
write() system call, after every SQL statement and before the
client is notified about the result. (This is not true if you are running
with delayed_key_writes, in which case only the data is written.)
This means that the data is safe even if mysqld crashes, as the OS will
ensure that the not flushed data is written to disk. You can force
MySQL to sync everything to disk after every SQL command by
starting mysqld with --flush.
The above means that normally you shouldn't get corrupted tables unless:
mysqld or the machine in the middle
of an update.
mysqld that caused it to die in the
middle of an update.
mysqld servers on the same data on a
system that doesn't support good file system locks (normally handled by
the lockd deamon ) or if you are running
multiple servers with --skip-locking
ALTER TABLE on a
repaired copy of the table!
Because it is very difficult to know why something is crashing, first try to check whether or not things that work for others crash for you. Please try the following things:
mysqld daemon with mysqladmin shutdown, run
myisamchk --silent --force */*.MYI on all tables, and restart the
mysqld daemon. This will ensure that you are running from a clean
state. See section 15 Maintaining a MySQL Installation.
mysqld --log and try to determine from the information in the log
whether or not some specific query kills the server. About 95% of all bugs are
related to a particular query! Normally this is one of the last queries in
the log file just before MySQL restarted.
You may be able to verify this using the following procedure:
mysqladmin shutdown).
myisamchk -s */*.MYI to verify that all
tables are correct. If any table is corrupted, repair it with
myisamchk -r path-to-table.MYI. You should take the backup
before checking the tables, as the problem could be related to corrupted
tables.
safe_mysqld --log-update or
safe_mysqld --log --log-update.
mysqld now dies, you have two options:
--datadir=/path/to/backup/).
mysqld.
You will not any lose information, because you have the log-update file.
mysql database_name < path-to-log-update-file.
You can also use the script mysql_find_rows to just execute some of the
update statements if you want to narrow down the problem.
If mysqld now crashes, then you have something repeatable
available. Please send mail to bugs@lists.mysql.com or
developers@mysql.com or (if you are a support customer) to
support@mysql.com about the problem and the MySQL team
will fix it as soon as possible.
fork_test.pl and fork2_test.pl.
--with-debug option to
configure and then recompile. See section H.1 Debugging a MySQL server.
--skip-locking option to mysqld. On some systems, the
lockd lock manager does not work properly; the --skip-locking
option tells mysqld not to use external locking. (This means that you
cannot run 2 mysqld servers on the same data and that you must be
careful if you use myisamchk, but it may be instructive to try the
option as a test.)
mysqladmin -u root processlist when mysqld
appears to be running but not responding? Sometimes mysqld is not
comatose even though you might think so. The problem may be that all
connections are in use, or there may be some internal lock problem.
mysqladmin processlist will usually be able to make a connection even
in these cases, and can provide useful information about the current number
of connections and their status.
mysqladmin -i 5 status or mysqladmin -i 5
-r status or in a separate window to produce statistics while you run
your other queries.
mysqld from gdb (or in another debugger).
mysqld has crashed inside
gdb:
backtrace info local up info local up info localWith gdb you can also examine which threads exist with
info
threads and switch to a specific thread with thread #, where
# is the thread id.
BLOB/TEXT columns (but only VARCHAR columns), you
can try to change all VARCHAR to CHAR with ALTER
TABLE. This will force MySQL to use fixed-size rows.
Fixed-size rows take a little extra space, but are much more tolerant to
corruption!
The current dynamic row code has been in use at MySQL AB for at least 3
years without any problems, but by nature dynamic-length rows are more
prone to errors, so it may be a good idea to try the above to see if it helps!
If you are linking your program and you get errors for unreferenced
symbols that start with mysql_, like the following:
/tmp/ccFKsdPa.o: In function `main': /tmp/ccFKsdPa.o(.text+0xb): undefined reference to `mysql_init' /tmp/ccFKsdPa.o(.text+0x31): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x57): undefined reference to `mysql_real_connect' /tmp/ccFKsdPa.o(.text+0x69): undefined reference to `mysql_error' /tmp/ccFKsdPa.o(.text+0x9a): undefined reference to `mysql_close'
you should be able to solve this by adding -Lpath-to-the-mysql-library
-lmysqlclient LAST on your link line.
If you get undefined reference errors for the compress function,
add -lgz LAST on your link line and try again!
If you get undefined reference errors for functions that should
exist on your system, like connect, check the man page for the
function in question, for which libraries you should add to the link
line!
If you get undefined reference errors for functions that don't
exist on your system, like the following:
mf_format.o(.text+0x201): undefined reference to `__lxstat'
it usually means that your library is compiled on a system that is not 100 % compatible with yours. In this case you should download the latest MySQL source distribution and compile this yourself. See section 4.7 Installing a MySQL Source Distribution.
If you are trying to run a program and you then get errors for
unreferenced symbols that start with mysql_ or that the
mysqlclient library can't be found, this means that your system
can't find the share libmysqlclient.so library.
The fix for this is to tell your system to search after shared libraries where the library is located by one of the following methods:
libmysqlclient.so the
LD_LIBRARY_PATH environment variable.
libmysqlclient.so the
LD_LIBRARY environment variable.
libmysqlclient.so to some place that is searched by your system,
like `/lib', and update the shared library information by executing
ldconfig.
Another way to solve this problem is to link your program statically, with
-static, or by removing the dynamic MySQL libraries
before linking your code. In the second case you should be
sure that no other programs are using the dynamic libraries!
MySQL server has gone away Error
This section also covers the related Lost connection to server
during query error.
The most common reason for the MySQL server has gone away error
is that the server timed out and closed the connection. By default, the
server closes the connection after 8 hours if nothing has happened. You
can change the time limit by setting the wait_timeout variable when
you start mysqld.
You can check that the MySQL hasn't died by executing
mysqladmin version and examining the uptime.
If you have a script, you just have to issue the query again for the client to do an automatic reconnection.
You normally can get the following error codes in this case (which one you get is OS-dependent):
CR_SERVER_GONE_ERROR | The client couldn't send a question to the server. |
CR_SERVER_LOST | The client didn't get an error when writing to the server, but it didn't get a full answer (or any answer) to the question. |
You can also get these errors if you send a query to the server that is
incorrect or too large. If mysqld gets a packet that is too large
or out of order, it assumes that something has gone wrong with the client and
closes the connection. If you need big queries (for example, if you are
working with big BLOB columns), you can increase the query limit by
starting mysqld with the -O max_allowed_packet=# option
(default 1M). The extra memory is allocated on demand, so mysqld will
use more memory only when you issue a big query or when mysqld must
return a big result row!
Can't connect to [local] MySQL server error
A MySQL client on Unix can connect to the mysqld server in two
different ways: Unix sockets, which connect through a file in the file
system (default `/tmp/mysqld.sock') or TCP/IP, which connects
through a port number. Unix sockets are faster than TCP/IP but can only
be used when connecting to a server on the same computer. Unix sockets
are used if you don't specify a hostname or if you specify the special
hostname localhost.
On Windows you can connect only with TCP/IP if the mysqld server
is running on Win95/Win98. If it's running on NT, you can also connect
with named pipes. The name of the named pipe is MySQL. If you
don't give a hostname when connecting to mysqld, a MySQL client
will first try to connect to the named pipe, and if this doesn't work it
will connect to the TCP/IP port. You can force the use of named pipes
on Windows by using . as the hostname.
The error (2002) Can't connect to ... normally means that there
isn't a MySQL server running on the system or that you are
using a wrong socket file or TCP/IP port when trying to connect to the
mysqld server.
Start by checking (using ps or the task manager on Windows) that
there is a process running named mysqld on your server! If there
isn't any mysqld process, you should start one. See section 4.16.2 Problems Starting the MySQL Server.
If a mysqld process is running, you can check the server by
trying these different connections (the port number and socket pathname
might be different in your setup, of course):
shell> mysqladmin version shell> mysqladmin variables shell> mysqladmin -h `hostname` version variables shell> mysqladmin -h `hostname` --port=3306 version shell> mysqladmin -h 'ip for your host' version shell> mysqladmin --socket=/tmp/mysql.sock version
Note the use of backquotes rather than forward quotes with the hostname
command; these cause the output of hostname (that is, the current
hostname) to be substituted into the mysqladmin command.
Here are some reasons the Can't connect to local MySQL server
error might occur:
mysqld is not running.
mysqld
uses the MIT-pthreads package.
See section 4.2 Operating Systems Supported by MySQL.
However, MIT-pthreads doesn't support Unix sockets, so on such a system you
must always specify the hostname explicitly when connecting to the server.
Try using this command to check the connection to the server:
shell> mysqladmin -h `hostname` version
mysqld uses (default
`/tmp/mysqld.sock'). You might have a cron job that removes the
MySQL socket (for example, a job that removes old files from the `/tmp'
directory). You can always run mysqladmin version and
check that the socket mysqladmin is trying to use really exists.
The fix in this case is to change the cron job to not remove
`mysqld.sock' or to place the socket somewhere else. You can specify
a different socket location at MySQL configuration time with this
command:
shell> ./configure --with-unix-socket-path=/path/to/socketYou can also start
safe_mysqld with the
--socket=/path/to/socket option and set the environment variable
MYSQL_UNIX_PORT to the socket pathname before starting your
MySQL clients.
mysqld server with
the --socket=/path/to/socket option. If you change the socket
pathname for the server, you must also notify the MySQL clients
about the new path. You can do this by setting the environment variable
MYSQL_UNIX_PORT to the socket pathname or by providing the socket path
as an argument to the clients. You can test the socket with this command:
shell> mysqladmin --socket=/path/to/socket version
mysqld threads (for example, with the
mysql_zap script before you can start a new MySQL
server. See section 20.2 What to Do if MySQL Keeps Crashing.
If you get the error message Can't connect to MySQL server on
some_hostname, you can try the following things to find out what the
problem is :
telnet your-host-name
tcp-ip-port-number and press RETURN a couple of times. If there
is a MySQL server running on this port you should get a
responses that includes the version number of the running MySQL
server. If you get an error like telnet: Unable to connect to
remote host: Connection refused, then there is no server running on the
given port.
mysqld daemon on the local machine and check
the TCP/IP port that mysqld it's configured to use (variable port) with
mysqladmin variables.
mysqld server is not started with the
--skip-networking option.
Host '...' is blocked ErrorIf you get an error like this:
Host 'hostname' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'
this means that mysqld has gotten a lot (max_connect_errors)
of connect requests from the host 'hostname' that have been interrupted
in the middle. After max_connect_errors failed requests, mysqld
assumes that something is wrong (like an attack from a cracker), and
blocks the site from further connections until someone executes the command
mysqladmin flush-hosts.
By default, mysqld blocks a host after 10 connection errors.
You can easily adjust this by starting the server like this:
shell> safe_mysqld -O max_connect_errors=10000 &
Note that if you get this error message for a given host, you should first
check that there isn't anything wrong with TCP/IP connections from that
host. If your TCP/IP connections aren't working, it won't do you any good to
increase the value of the max_connect_errors variable!
Too many connections Error
If you get the error Too many connections when you try to connect
to MySQL, this means that there is already max_connections
clients connected to the mysqld server.
If you need more connections than the default (100), then you should restart
mysqld with a bigger value for the max_connections variable.
Note that mysqld actually allows (max_connections+1)
clients to connect. The last connection is reserved for a user with the
process privilege. By not giving this privilege to normal
users (they shouldn't need this), an administrator with this privilege
can log in and use SHOW PROCESSLIST to find out what could be
wrong. See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
The maximum number of connects MySQL is depending on how good the thread library is on a given platform. Linux or Solaris should be able to support 500-1000 simultaneous connections, depending on how much RAM you have and what your clients are doing.
Out of memory ErrorIf you issue a query and get something like the following error:
mysql: Out of memory at line 42, 'malloc.c' mysql: needed 8136 byte (8k), memory in use: 12481367 bytes (12189k) ERROR 2008: MySQL client ran out of memory
note that the error refers to the MySQL client mysql. The
reason for this error is simply that the client does not have enough memory to
store the whole result.
To remedy the problem, first check that your query is correct. Is it
reasonable that it should return so many rows? If so,
you can use mysql --quick, which uses mysql_use_result()
to retrieve the result set. This places less of a load on the client (but
more on the server).
Packet too large Error
When a MySQL client or the mysqld server gets a packet bigger
than max_allowed_packet bytes, it issues a Packet too large
error and closes the connection.
If you are using the mysql client, you may specify a bigger buffer by
starting the client with mysql --set-variable=max_allowed_packet=8M.
If you are using other clients that do not allow you to specify the maximum
packet size (such as DBI), you need to set the packet size when you
start the server. You cau use a command-line option to mysqld to set
max_allowed_packet to a larger size. For example, if you are
expecting to store the full length of a BLOB into a table, you'll need
to start the server with the --set-variable=max_allowed_packet=16M
option.
If you find the error Aborted connection in the hostname.err
log file, this could be because of one of the following reasons:
wait_timeout without doing
any requests. See section 7.28.4 SHOW VARIABLES.
mysql_close() before exit.
The table is full Error
This error occurs in older MySQL versions when an in-memory temporary
table becomes larger than tmp_table_size bytes. To avoid this
problem, you can use the -O tmp_table_size=# option to
mysqld to increase the temporary table size or use the SQL
option SQL_BIG_TABLES before you issue the problematic
query. See section 7.33 SET Syntax.
You can also start mysqld with the --big-tables option.
This is exactly the same as using SQL_BIG_TABLES for all queries.
In MySQL Version 3.23, in-memory temporary tables will automatically be
converted to a disk-based MyISAM table after the table size gets
bigger than tmp_table_size.
Can't create/write to file ErrorIf you get an error for some queries of type:
Can't create/write to file '\\sqla3fe_0.ism'.
this means that MySQL can't create a temporary file for the
result set in the given temporary directory. (The above error is a
typical error message on Windows, and the Unix error message is similar.)
The fix is to start mysqld with --tmpdir=path or to add to your option
file:
[mysqld] tmpdir=C:/temp
assuming that the `c:\\temp' directory exists. See section 4.16.5 Option Files.
Check also the error code that you get with perror. One reason
may also be a disk full error;
shell >perror 28 Error code 28: No space left on device
Commands out of sync Error in Client
If you get Commands out of sync; You can't run this command now
in your client code, you are calling client functions in the wrong order!
This can happen, for example, if you are using mysql_use_result() and
try to execute a new query before you have called mysql_free_result().
It can also happen if you try to execute two queries that return data without
a mysql_use_result() or mysql_store_result() in between.
Ignoring user ErrorIf you get the following error:
Found wrong password for user: 'some_user@some_host'; Ignoring user
this means that when mysqld was started or when it reloaded the
permissions tables, it found an entry in the user table with
an invalid password. As a result, the entry is simply ignored by the
permission system.
Possible causes of and fixes for this problem:
mysqld with an old
user table.
You can check this by executing mysqlshow mysql user to see if
the password field is shorter than 16 characters. If so, you can correct this
condition by running the scripts/add_long_password script.
mysqld with the --old-protocol option.
Update the user in the user table with a new password or
restart mysqld with --old-protocol.
user table without using the
PASSWORD() function. Use mysql to update the user in the
user table with a new password. Make sure to use the PASSWORD()
function:
mysql> update user set password=PASSWORD('your password')
where user='XXX';
Table 'xxx' doesn't exist Error
If you get the error Table 'xxx' doesn't exist or Can't
find file: 'xxx' (errno: 2), this means that no table exists
in the current database with the name xxx.
Note that as MySQL uses directories and files to store databases and tables, the database and table names are case sensitive! (On Windows the databases and tables names are not case sensitive, but all references to a given table within a query must use the same case!)
You can check which tables you have in the current database with
SHOW TABLES. See section 7.28 SHOW Syntax (Get Information About Tables, Columns,...).
When a disk-full condition occurs, MySQL does the following:
To alleviate the problem, you can take the following actions:
mysqladmin kill to the thread.
The thread will be aborted the next time it checks the disk (in 1 minute).
The mysql client typically is used interactively, like this:
shell> mysql database
However, it's also possible to put your SQL commands in a file and tell
mysql to read its input from that file. To do so, create a text
file `text_file' that contains the commands you wish to execute.
Then invoke mysql as shown below:
shell> mysql database < text_file
You can also start your text file with a USE db_name statement. In
this case, it is unnecessary to specify the database name on the command
line:
shell> mysql < text_file
See section 14.1 Overview of the Different MySQL Programs.
MySQL uses the value of the TMPDIR environment variable as
the pathname of the directory in which to store temporary files. If you don't
have TMPDIR set, MySQL uses the system default, which is
normally `/tmp' or `/usr/tmp'. If the file system containing your
temporary file directory is too small, you should edit safe_mysqld to
set TMPDIR to point to a directory in a file system where you have
enough space! You can also set the temporary directory using the
--tmpdir option to mysqld.
MySQL creates all temporary files as hidden files. This ensures
that the temporary files will be removed if mysqld is terminated. The
disadvantage of using hidden files is that you will not see a big temporary
file that fills up the file system in which the temporary file directory is
located.
When sorting (ORDER BY or GROUP BY), MySQL normally
uses one or two temporary files. The maximum disk-space needed is:
(length of what is sorted + sizeof(database pointer)) * number of matched rows * 2
sizeof(database pointer) is usually 4, but may grow in the future for
really big tables.
For some SELECT queries, MySQL also creates temporary SQL
tables. These are not hidden and have names of the form `SQL_*'.
ALTER TABLE creates a temporary table in the same directory as
the original table.
If you have problems with the fact that anyone can delete the
MySQL communication socket `/tmp/mysql.sock', you can,
on most versions of Unix, protect your `/tmp' file system by setting
the sticky bit on it. Log in as root and do the following:
shell> chmod +t /tmp
This will protect your `/tmp' file system so that files can be deleted
only by their owners or the superuser (root).
You can check if the sticky bit is set by executing ls -ld /tmp.
If the last permission bit is t, the bit is set.
Access denied Error
See section 6.8 How the Privilege System Works, and especially see See section 6.15 Causes of Access denied Errors.
The MySQL server mysqld can be started and run by any user.
In order to change mysqld to run as a Unix user user_name, you must
do the following:
mysqladmin shutdown).
user_name has
privileges to read and write files in them (you may need to do this as
the Unix root user):
shell> chown -R user_name /path/to/mysql/datadirIf directories or files within the MySQL data directory are symlinks, you'll also need to follow those links and change the directories and files they point to.
chown -R may not follow symlinks for
you.
user_name, or, if you are using
MySQL Version 3.22 or later, start mysqld as the Unix root
user and use the --user=user_name option. mysqld will switch
to run as the Unix user user_name before accepting any connections.
mysql.server script to start mysqld when
the system is rebooted, you should edit mysql.server to use su
to run mysqld as user user_name, or to invoke mysqld
with the --user option. (No changes to safe_mysqld are
necessary.)
At this point, your mysqld process should be running fine and dandy as
the Unix user user_name. One thing hasn't changed, though: the
contents of the permissions tables. By default (right after running the
permissions table install script mysql_install_db), the MySQL
user root is the only user with permission to access the mysql
database or to create or drop databases. Unless you have changed those
permissions, they still hold. This shouldn't stop you from accessing
MySQL as the MySQL root user when you're logged in
as a Unix user other than root; just specify the -u root option
to the client program.
Note that accessing MySQL as root, by supplying -u
root on the command line, has nothing to do with MySQL running
as the Unix root user, or, indeed, as another Unix user. The access
permissions and user names of MySQL are completely separate from
Unix user names. The only connection with Unix user names is that if you
don't provide a -u option when you invoke a client program, the client
will try to connect using your Unix login name as your MySQL user
name.
If your Unix box itself isn't secured, you should probably at least put a
password on the MySQL root users in the access tables.
Otherwise, any user with an account on that machine can run mysql -u
root db_name and do whatever he likes.
If you have forgotten the root user password for MySQL, you
can restore it with the following procedure:
kill (not kill
-9) to the mysqld server. The pid is stored in a .pid
file, which is normally in the MySQL database directory:
kill `cat /mysql-data-directory/hostname.pid`You must be either the Unix
root user or the same user the server
runs as to do this.
mysqld with the --skip-grant-tables option.
mysql -h hostname mysql and change
the password with a GRANT command. See section 7.34 GRANT and REVOKE Syntax.
You can also do this with
mysqladmin -h hostname -u user password 'new password'
mysqladmin -h hostname
flush-privileges or with the SQL command FLUSH PRIVILEGES.
Note that after you started mysqld with --skip-grant-tables,
any usage of GRANT commands will give you an Unknown command
error until you have executed FLUSH PRIVILEGES.
If you have problems with file permissions, for example, if mysql
issues the following error message when you create a table:
ERROR: Can't find file: 'path/with/filename.frm' (Errcode: 13)
then the environment variable UMASK might be set incorrectly when
mysqld starts up. The default umask value is 0660. You can
change this behavior by starting safe_mysqld as follows:
shell> UMASK=384 # = 600 in octal shell> export UMASK shell> /path/to/safe_mysqld &
By default MySQL will create database and RAID
directories with permission type 0700. You can modify this behavior by
setting the UMASK_DIR variable. If you set this, new
directories are created with the combined UMASK and
UMASK_DIR. For example, if you want to give group access to
all new directories, you can do:
shell> UMASK_DIR=504 # = 770 in octal shell> export UMASK_DIR shell> /path/to/safe_mysqld &
In MySQL Version 3.23.25 and above, MySQL assumes that the
value for UMASK and UMASK_DIR is in octal if it starts
with a zero.
See section A Environment Variables.
If you get ERROR '...' not found (errno: 23), Can't open
file: ... (errno: 24), or any other error with errno 23 or
errno 24 from MySQL, it means that you haven't allocated
enough file descriptors for MySQL. You can use the
perror utility to get a description of what the error number
means:
shell> perror 23 File table overflow shell> perror 24 Too many open files
The problem here is that mysqld is trying to keep open too many
files simultaneously. You can either tell mysqld not to open so
many files at once or increase the number of file descriptors
available to mysqld.
To tell mysqld to keep open fewer files at a time, you can make the
table cache smaller by using the -O table_cache=32 option
to safe_mysqld (the default value is 64). Reducing the value of
max_connections will also reduce the number of open files (the default
value is 90).
To change the number of file descriptors available to mysqld, modify
the safe_mysqld script. There is a commented-out line
ulimit -n 256 in the script. You can remove the '#' character
to uncomment this line, and change the number 256 to change the number of
file descriptors available to mysqld.
ulimit can increase the number of file descriptors, but only up to the
limit imposed by the operating system. If you need to increase the OS limit
on the number of file descriptors available to each process, consult the
documentation for your operating system.
Note that if you run the tcsh shell, ulimit will not work!
tcsh will also report incorrect values when you ask for the current
limits! In this case you should start safe_mysqld with sh!
DATE Columns
The format of a DATE value is 'YYYY-MM-DD'. According to ANSI
SQL, no other format is allowed. You should use this format in UPDATE
expressions and in the WHERE clause of SELECT statements. For
example:
mysql> SELECT * FROM tbl_name WHERE date >= '1997-05-05';
As a convenience, MySQL automatically converts a date to a number if
the date is used in a numeric context (and vice versa). It is also smart
enough to allow a ``relaxed'' string form when updating and in a WHERE
clause that compares a date to a TIMESTAMP, DATE, or a
DATETIME column. (Relaxed form means that any punctuation character
may be used as the separator between parts. For example, '1998-08-15'
and '1998#08#15' are equivalent.) MySQL can also convert a
string containing no separators (such as '19980815'), provided it
makes sense as a date.
The special date '0000-00-00' can be stored and retrieved as
'0000-00-00'. When using a '0000-00-00' date through
MyODBC, it will automatically be converted to NULL in
MyODBC Version 2.50.12 and above, because ODBC can't handle this kind of
date.
Because MySQL performs the conversions described above, the following statements work:
mysql> INSERT INTO tbl_name (idate) VALUES (19970505);
mysql> INSERT INTO tbl_name (idate) VALUES ('19970505');
mysql> INSERT INTO tbl_name (idate) VALUES ('97-05-05');
mysql> INSERT INTO tbl_name (idate) VALUES ('1997.05.05');
mysql> INSERT INTO tbl_name (idate) VALUES ('1997 05 05');
mysql> INSERT INTO tbl_name (idate) VALUES ('0000-00-00');
mysql> SELECT idate FROM tbl_name WHERE idate >= '1997-05-05';
mysql> SELECT idate FROM tbl_name WHERE idate >= 19970505;
mysql> SELECT mod(idate,100) FROM tbl_name WHERE idate >= 19970505;
mysql> SELECT idate FROM tbl_name WHERE idate >= '19970505';
However, the following will not work:
mysql> SELECT idate FROM tbl_name WHERE STRCMP(idate,'19970505')=0;
STRCMP() is a string function, so it converts idate to
a string and performs a string comparison. It does not convert
'19970505' to a date and perform a date comparison.
Note that MySQL does no checking whether or not the date is
correct. If you store an incorrect date, such as '1998-2-31', the
wrong date will be stored. If the date cannot be converted to any reasonable
value, a 0 is stored in the DATE field. This is mainly a speed
issue and we think it is up to the application to check the dates, and not
the server.
If you have a problem with SELECT NOW() returning values in GMT and
not your local time, you have to set the TZ environment variable to
your current time zone. This should be done for the environment in which
the server runs, for example, in safe_mysqld or mysql.server.
See section A Environment Variables.
By default, MySQL searches are case-insensitive (although there are
some character sets that are never case insensitive, such as czech).
That means that if you search with col_name LIKE 'a%', you will get all
column values that start with A or a. If you want to make this
search case-sensitive, use something like INDEX(col_name, "A")=0 to
check a prefix. Or use STRCMP(col_name, "A") = 0 if the column value
must be exactly "A".
Simple comparison operations (>=, >, = , < , <=, sorting and
grouping) are based on each character's ``sort value''. Characters with
the same sort value (like E, e and é) are treated as the same character!
In older MySQL versions LIKE comparisons where done on
the uppercase value of each character (E == e but E <> é). In newer
MySQL versions LIKE works just like the other comparison
operators.
If you want a column always to be treated in case-sensitive fashion,
declare it as BINARY. See section 7.7 CREATE TABLE Syntax.
If you are using Chinese data in the so-called big5 encoding, you want to
make all character columns BINARY. This works because the sorting
order of big5 encoding characters is based on the order of ASCII codes.
NULL Values
The concept of the NULL value is a common source of confusion for
newcomers to SQL, who often think that NULL is the same thing as an
empty string ''. This is not the case! For example, the following
statements are completely different:
mysql> INSERT INTO my_table (phone) VALUES (NULL);
mysql> INSERT INTO my_table (phone) VALUES ("");
Both statements insert a value into the phone column, but the first
inserts a NULL value and the second inserts an empty string. The
meaning of the first can be regarded as ``phone number is not known'' and the
meaning of the second can be regarded as ``she has no phone''.
In SQL, the NULL value is always false in comparison to any
other value, even NULL. An expression that contains NULL
always produces a NULL value unless otherwise indicated in
the documentation for the operators and functions involved in the
expression. All columns in the following example return NULL:
mysql> SELECT NULL,1+NULL,CONCAT('Invisible',NULL);
If you want to search for column values that are NULL, you
cannot use the =NULL test. The following statement returns no
rows, because expr = NULL is FALSE, for any expression:
mysql> SELECT * FROM my_table WHERE phone = NULL;
To look for NULL values, you must use the IS NULL test.
The following shows how to find the NULL phone number and the
empty phone number:
mysql> SELECT * FROM my_table WHERE phone IS NULL; mysql> SELECT * FROM my_table WHERE phone = "";
In MySQL, as in many other SQL servers, you can't index
columns that can have NULL values. You must declare such columns
NOT NULL. Conversely, you cannot insert NULL into an indexed
column.
When reading data with LOAD DATA INFILE, empty columns are updated
with ''. If you want a NULL value in a column, you should use
\N in the text file. The literal word 'NULL' may also be used
under some circumstances.
See section 7.23 LOAD DATA INFILE Syntax.
When using ORDER BY, NULL values are presented first. If you
sort in descending order using DESC, NULL values are presented
last. When using GROUP BY, all NULL values are regarded as
equal.
To help with NULL handling, you can use the IS NULL and
IS NOT NULL operators and the IFNULL() function.
For some column types, NULL values are handled specially. If you
insert NULL into the first TIMESTAMP column of a table, the
current date and time is inserted. If you insert NULL into an
AUTO_INCREMENT column, the next number in the sequence is inserted.
alias
You can use an alias to refer to a column in the GROUP BY,
ORDER BY, or in the HAVING part. Aliases can also be used
to give columns better names:
SELECT SQRT(a*b) as rt FROM table_name GROUP BY rt HAVING rt > 0; SELECT id,COUNT(*) AS cnt FROM table_name GROUP BY id HAVING cnt > 0; SELECT id AS "Customer identity" FROM table_name;
Note that ANSI SQL doesn't allow you to refer to an alias in a
WHERE clause. This is because when the WHERE code is
executed the column value may not yet be determined. For example, the
following query is illegal:
SELECT id,COUNT(*) AS cnt FROM table_name WHERE cnt > 0 GROUP BY id;
The WHERE statement is executed to determine which rows should
be included in the GROUP BY part while HAVING is used to
decide which rows from the result set should be used.
As MySQL doesn't support sub-selects or use of more than one table
in the DELETE statement, you should use the following approach to
delete rows from 2 related tables:
SELECT the rows based on some WHERE condition in the main table.
DELETE the rows in the main table based on the same condition.
DELETE FROM related_table WHERE related_column IN (selected_rows).
If the total number of characters in the query with
related_column is more than 1,048,576 (the default value of
max_allowed_packet, you should split it into smaller parts and
execute multiple DELETE statements. You will probably get the
fastest DELETE by only deleting 100-1000 related_column
id's per query if the related_column is an index. If the
related_column isn't an index, the speed is independent of the
number of arguments in the IN clause.
If you have a complicated query that has many tables and that doesn't return any rows, you should use the following procedure to find out what is wrong with your query:
EXPLAIN and check if you can find something that is
obviously wrong. See section 7.29 EXPLAIN Syntax (Get Information About a SELECT).
WHERE clause.
LIMIT 10 with the query.
SELECT for the column that should have matched a row against
the table that was last removed from the query.
FLOAT or DOUBLE columns with numbers that
have decimals, you can't use =! This problem is common in most
computer languages because floating-point values are not exact values:
mysql> SELECT * FROM table_name WHERE float_column=3.5; -> mysql> SELECT * FROM table_name WHERE float_column between 3.45 and 3.55;In most cases, changing the
FLOAT to a DOUBLE will fix this!
mysql test < query.sql that shows your problems.
You can create a test file with mysqldump --quick database tables > query.sql. Open the file in an editor, remove some insert lines (if there are
too many of these), and add your select statement at the end of the file.
Test that you still have your problem by doing:
shell> mysqladmin create test2 shell> mysql test2 < query.sqlPost the test file using
mysqlbug to mysql@lists.mysql.com.
ALTER TABLE.
If ALTER TABLE dies with an error like this:
Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17)
the problem may be that MySQL has crashed in a previous ALTER
TABLE and there is an old table named `A-something' or
`B-something' lying around. In this case, go to the MySQL data
directory and delete all files that have names starting with A- or
B-. (You may want to move them elsewhere instead of deleting them.)
ALTER TABLE works the following way:
If something goes wrong with the renaming operation, MySQL tries to undo the changes. If something goes seriously wrong (this shouldn't happen, of course), MySQL may leave the old table as `B-xxx', but a simple rename should get your data back.
The whole point of SQL is to abstract the application from the data storage format. You should always specify the order in which you wish to retrieve your data. For example:
SELECT col_name1, col_name2, col_name3 FROM tbl_name;
will return columns in the order col_name1, col_name2, col_name3, whereas:
SELECT col_name1, col_name3, col_name2 FROM tbl_name;
will return columns in the order col_name1, col_name3, col_name2.
You should NEVER, in an application, use SELECT * and
retrieve the columns based on their position, because the order in which
columns are returned CANNOT be guaranteed over time. A simple
change to your database may cause your application to fail rather
dramatically.
If you want to change the order of columns anyway, you can do it as follows:
INSERT INTO new_table SELECT fields-in-new_table-order FROM old_table.
old_table.
ALTER TABLE new_table RENAME old_table.
Now that master-slave internal replication is available starting in Version 3.23.15, this is the recommended way. See section 11 Replication in MySQL.
However, it is still possible to replicate a database by using the
update log. See section 21.3 The Update Log. This requires one database that acts as a
master (to which data changes are made) and one or more other databases
that act as slaves. To update a slave, just run mysql <
update_log. Supply host, user, and password options that are
appropriate for the slave database, and use the update log from the
master database as input.
If you never delete anything from a table, you can use a TIMESTAMP
column to find out which rows have been inserted or changed in the table
since the last replication (by comparing the time when you did the
replication last time) and only copy these rows to the mirror.
It is possible to make a two-way updating system using both the update log (for deletes) and timestamps (on both sides). But in that case you must be able to handle conflicts when the same data have been changed in both ends. You probably want to keep the old version to help with deciding what has been updated.
Because replication in this case is done with SQL statements, you should not use the following functions in statements that update the database; they may not return the same value as in the original database:
DATABASE()
GET_LOCK() and RELEASE_LOCK()
RAND()
USER(), SYSTEM_USER() or SESSION_USER()
VERSION(), CONNECT_ID()
All time functions are safe to use, as the timestamp is sent to the
mirror if needed. LAST_INSERT_ID() is also safe to use.
Because MySQL tables are stored as files, it is easy to do a
backup. To get a consistent backup, do a LOCK TABLES on the
relevant tables. See section 7.32 LOCK TABLES/UNLOCK TABLES Syntax. You only need a
read lock; this allows other threads to continue to query the tables while
you are making a copy of the files in the database directory. If you want to
make a SQL level backup of a table, you can use SELECT INTO OUTFILE.
Another way to back up a database is to use the mysqldump program:
See section 14.6 Dumping the Structure and Data from MySQL Databases and Tables.
shell> mysqldump --tab=/path/to/some/dir --opt --fullYou can also simply copy all table files (`*.frm', `*.MYD', and `*.MYI' files) as long as the server isn't updating anything. The script
mysqlhotcopy does use this method.
mysqld if it's running, then start it with the
--log-update[=file_name] option. See section 21.3 The Update Log. The update
log file(s) provide you with the information you need to replicate
changes to the database that are made subsequent to the point at which
you executed mysqldump.
If you have to restore something, try to recover your tables using
myisamchk -r first. That should work in 99.9% of all cases. If
myisamchk fails, try the following procedure:
(This will only work if you have started MySQL with
--log-update. See section 21.3 The Update Log.):
mysqldump backup.
shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql
ls is used to get all the update log files in the right order.
You can also do selective backups with SELECT * INTO OUTFILE 'file_name'
FROM tbl_name and restore with LOAD DATA INFILE 'file_name' REPLACE
... To avoid duplicate records, you need a PRIMARY KEY or a
UNIQUE key in the table. The REPLACE keyword causes old records
to be replaced with new ones when a new record duplicates an old record on
a unique key value.
When started with the --log-update[=file_name] option,
mysqld writes a log file containing all SQL commands that update
data. If no filename is given, it defaults to the name of the host
machine. If a filename is given, but it doesn't contain a path, the file
is written in the data directory. If file_name doesn't have an
extension, mysqld will create log file names of type
file_name.#, where # is a number that is incremented each
time you execute mysqladmin refresh, execute mysqladmin
flush-logs, execute the FLUSH LOGS statement, or restart the server.
NOTE: For the above scheme to work, you should NOT create your own files with the same filename as the update log + some extensions that may be regarded as a number, in the directory used by the update log!
If you use the --log or -l options, mysqld writes a
general log with a filename of `hostname.log', and restarts and
refreshes do not cause a new log file to be generated (although it is closed
and reopened). In this case you can copy it (on Unix) by doing:
mv hostname.log hostname-old.log mysqladmin flush-logs cp hostname-old.log to-backup-directory rm hostname-old.log
By default, the mysql.server script starts the MySQL
server with the -l option. If you need better performance when
you start using MySQL in a production environment, you can
remove the -l option from mysql.server or change it to
--log-update.
Update logging is smart because it logs only statements that really update
data. So an UPDATE or a DELETE with a WHERE that finds no
rows is not written to the log. It even skips UPDATE statements that
set a column to the value it already has.
If you want to update a database from update log files, you could do the following (assuming your update logs have names of the form `file_name.###'):
shell> ls -1 -t -r file_name.[0-9]* | xargs cat | mysql
ls is used to get all the log files in the right order.
This can be useful if you have to revert to backup files after a crash and you want to redo the updates that occurred between the time of the backup and the crash.
In the future the binary log will replace the update log, so we recommend you to switch to this log format as soon as possible!
The binary log contains all information that is available in the update log in a more efficient format. It also contains information about how long every query that updated the database took.
The binary log is also used when you are replicating a slave from a master. See section 11 Replication in MySQL.
When started with the --log-bin[=file_name] option, mysqld
writes a log file containing all SQL commands that update data. If no
file name is given, it defaults to the name of the host machine followed
by -bin. If file name is given, but it doesn't contain a path, the
file is written in the data directory.
To the binary log filename mysqld will append an extension that is a
number that is incremented each time you execute mysqladmin
refresh, execute mysqladmin flush-logs, execute the FLUSH LOGS
statement or restart the server.
To be able to know which different binary log files have been used,
mysqld will also create a binary log index file that
contains the name of all used binary log files. By default this has the
same name as the binary log file, with the extension '.index'.
You can change the name of the binary log index file with the
--log-bin-index=[filename] option.
If you are using replication, you should not delete old binary log
files until you are sure that no slave will ever need to use them.
One way to do this is to do mysqladmin flush-logs once a day and then
remove any logs that are more than 3 days old.
You can examine the binary log file with the mysqlbinlib command.
For example, you can update a MySQL server from the binary log
as follows:
mysqlbinlog log-file | mysql -h server_name
You can also use the `mysqlbinlog' program to read the binary log direct from a remote mysql server!
mysqlbinlog --help will give you more information of how to use
this program!
If you are using BEGIN or SET AUTO_COMMIT=0, you must use
the MySQL binary log for backups instead of the old update log.
All updates (UPDATE, DELETE or INSERT) that changes
a transactional table (like BDB tables) is cached until a COMMIT.
Any updates to a not transactional table is stored in the binary log at
once. Every thread will on start allocate a buffer of
binlog_cache_size to buffer queries. If a query is bigger than
this, the thread will open a temporary file to handle the bigger cache.
The temporary file will be deleted when the thread ends.
The max_binlog_cache_size can be used to restrict the total size used
to cache a multi-transaction query.
When started with the --log-slow-queries[=file_name] option,
mysqld writes a log file containing all SQL commands that took
more than long_query_time to execute. The time to get the initial
table locks are not counted as execution time.
If no file name is given, it defaults to the name of the host machine
suffixed with -slow.log. If a filename is given, but doesn't
contain a path, the file is written in the data directory.
The slow query log can be used to find queries that takes a long time to execute and are thus candidates for optimization.
You are using --log-long-format then also queries that are not
using indexes are printed. See section 4.16.4 Command-line Options.
You can also use the update logs when you have a mirrored database on another host and you want to replicate the changes that have been made to the master database. See section 21.1 Database Replication with Update Log.
There are circumstances when you might want to run multiple servers on the same machine. For example, you might want to test a new MySQL release while leaving your existing production setup undisturbed. Or you might be an Internet service provider that wants to provide independent MySQL installations for different customers.
If you want to run multiple servers, the easiest way is to compile the servers
with different TCP/IP ports and socket files so they are not
both listening to the same TCP/IP port or socket file. See section 14.3 mysqld_multi, program for managing multiple MySQL servers.
Assume an existing server is configured for the default port number and
socket file. Then configure the new server with a configure command
something like this:
shell> ./configure --with-tcp-port=port_number \
--with-unix-socket-path=file_name \
--prefix=/usr/local/mysql-3.22.9
Here port_number and file_name should be different than the
default port number and socket file pathname, and the --prefix value
should specify an installation directory different than the one under which
the existing MySQL installation is located.
You can check the socket and port used by any currently executing MySQL server with this command:
shell> mysqladmin -h hostname --port=port_number variables
If you have a MySQL server running on the port you used, you will get a list of some of the most important configurable variables in MySQL, including the socket name.
You don't have to recompile a new MySQL server just to start with
a different port and socket. You can change the port and socket to be used
by specifying them at run time as options to safe_mysqld:
shell> /path/to/safe_mysqld --socket=file_name --port=port_number
mysqld_multi can also take safe_mysqld (or mysqld)
as an argument and pass the options from a configuration file to
safe_mysqld and further to mysqld.
If you run the new server on the same database directory as another
server with logging enabled, you should also specify the name of the log
files to safe_mysqld with --log, --log-update, or
--log-slow-queries. Otherwise, both servers may be trying to
write to the same log file.
WARNING: Normally you should never have two servers that update data in the same database! If your OS doesn't support fault-free system locking, this may lead to unpleasant surprises!
If you want to use another database directory for the second server, you
can use the --datadir=path option to safe_mysqld.
NOTE also that starting several MySQL servers
(mysqlds) in different machines and letting them access one data
directory over NFS is generally a BAD IDEA! The problem
is that the NFS will become the bottleneck with the speed. It is
not meant for such use. And last but not least, you would still have to
come up with a solution how to make sure that two or more mysqlds
are not interfering with each other. At the moment there is no platform
that would 100% reliable do the file locking (lockd daemon
usually) in every situation. Yet there would be one more possible risk
with NFS; it would make the work even more complicated for
lockd daemon to handle. So make it easy for your self and forget
about the idea. The working solution is to have one computer with an
operating system that efficiently handles threads and have several CPUs
in it.
When you want to connect to a MySQL server that is running with a different port than the port that is compiled into your client, you can use one of the following methods:
--host 'hostname' --port=port_numer or
[--host localhost] --socket=file_name.
$dsn = "DBI:mysql:test;mysql_read_default_group=client;" $dbh = DBI->connect($dsn, $user, $password);
MYSQL_UNIX_PORT and MYSQL_TCP_PORT environment variables
to point to the Unix socket and TCP/IP port before you start your clients.
If you normally use a specific socket or port, you should place commands
to set these environment variables in your `.login' file.
See section A Environment Variables. See section 14.1 Overview of the Different MySQL Programs.
The C API code is distributed with MySQL. It is included in the
mysqlclient library and allows C programs to access a database.
Many of the clients in the MySQL source distribution are
written in C. If you are looking for examples that demonstrate how to
use the C API, take a look at these clients. You can find these in the
clients directory in the MySQL source distribution.
Most of the other client APIs (all except Java) use the mysqlclient
library to communicate with the MySQL server. This means that, for
example, you can take advantage of many of the same environment variables
that are used by other client programs, because they are referenced from the
library. See section 14.1 Overview of the Different MySQL Programs, for a list of these variables.
The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16K bytes) is automatically increased up to the maximum size (the maximum is 16M). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets.
The communication buffer must be large enough to contain a single SQL
statement (for client-to-server traffic) and one row of returned data (for
server-to-client traffic). Each thread's communication buffer is dynamically
enlarged to handle any query or row up to the maximum limit. For example, if
you have BLOB values that contain up to 16M of data, you must have a
communication buffer limit of at least 16M (in both server and client). The
client's default maximum is 16M, but the default maximum in the server is
1M. You can increase this by changing the value of the
max_allowed_packet parameter when the server is started. See section 12.2.3 Tuning Server Parameters.
The MySQL server shrinks each communication buffer to
net_buffer_length bytes after each query. For clients, the size of
the buffer associated with a connection is not decreased until the connection
is closed, at which time client memory is reclaimed.
For programming with threads, consult the 'how to make a thread-safe client' chapter. See section 22.4.57 How to Make a Thread-safe Client.
MYSQL
MYSQL_RES
SELECT, SHOW, DESCRIBE, EXPLAIN). The
information returned from a query is called the result set in the
remainder of this section.
MYSQL_ROW
mysql_fetch_row().
MYSQL_FIELD
MYSQL_FIELD structures for each field by
calling mysql_fetch_field() repeatedly. Field values are not part of
this structure; they are contained in a MYSQL_ROW structure.
MYSQL_FIELD_OFFSET
mysql_field_seek().) Offsets are field numbers
within a row, beginning at zero.
my_ulonglong
mysql_affected_rows(),
mysql_num_rows(), and mysql_insert_id(). This type provides a
range of 0 to 1.84e19.
On some systems, attempting to print a value of type my_ulonglong
will not work. To print such a value, convert it to unsigned long
and use a %lu print format. Example:
printf (Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));
The MYSQL_FIELD structure contains the members listed below:
char * name
char * table
table value is an empty string.
char * def
mysql_list_fields().
enum enum_field_types type
type value may be one of the following:
| Type value | Type meaning |
FIELD_TYPE_TINY | TINYINT field
|
FIELD_TYPE_SHORT | SMALLINT field
|
FIELD_TYPE_LONG | INTEGER field
|
FIELD_TYPE_INT24 | MEDIUMINT field
|
FIELD_TYPE_LONGLONG | BIGINT field
|
FIELD_TYPE_DECIMAL | DECIMAL or NUMERIC field
|
FIELD_TYPE_FLOAT | FLOAT field
|
FIELD_TYPE_DOUBLE | DOUBLE or REAL field
|
FIELD_TYPE_TIMESTAMP | TIMESTAMP field
|
FIELD_TYPE_DATE | DATE field
|
FIELD_TYPE_TIME | TIME field
|
FIELD_TYPE_DATETIME | DATETIME field
|
FIELD_TYPE_YEAR | YEAR field
|
FIELD_TYPE_STRING | String (CHAR or VARCHAR) field
|
FIELD_TYPE_BLOB | BLOB or TEXT field (use max_length to determine the maximum length)
|
FIELD_TYPE_SET | SET field
|
FIELD_TYPE_ENUM | ENUM field
|
FIELD_TYPE_NULL | NULL-type field
|
FIELD_TYPE_CHAR | Deprecated; use FIELD_TYPE_TINY instead
|
IS_NUM() macro to test whether or not a field has a
numeric type. Pass the type value to IS_NUM() and it
will evaluate to TRUE if the field is numeric:
if (IS_NUM(field->type))
printf("Field is numeric\n");
unsigned int length
unsigned int max_length
mysql_store_result() or mysql_list_fields(), this contains the
maximum length for the field. If you use mysql_use_result(), the
value of this variable is zero.
unsigned int flags
flags value may have zero
or more of the following bits set:
| Flag value | Flag meaning |
NOT_NULL_FLAG | Field can't be NULL
|
PRI_KEY_FLAG | Field is part of a primary key |
UNIQUE_KEY_FLAG | Field is part of a unique key |
MULTIPLE_KEY_FLAG | Field is part of a non-unique key |
UNSIGNED_FLAG | Field has the UNSIGNED attribute
|
ZEROFILL_FLAG | Field has the ZEROFILL attribute
|
BINARY_FLAG | Field has the BINARY attribute
|
AUTO_INCREMENT_FLAG | Field has the AUTO_INCREMENT
attribute
|
ENUM_FLAG | Field is an ENUM (deprecated)
|
BLOB_FLAG | Field is a BLOB or TEXT (deprecated)
|
TIMESTAMP_FLAG | Field is a TIMESTAMP (deprecated)
|
BLOB_FLAG, ENUM_FLAG, and TIMESTAMP_FLAG
flags is deprecated because they indicate the type of a field rather
than an attribute of its type. It is preferable to test
field->type against FIELD_TYPE_BLOB,
FIELD_TYPE_ENUM, or FIELD_TYPE_TIMESTAMP instead.
The example below illustrates a typical use of the flags value:
if (field->flags & NOT_NULL_FLAG)
printf("Field can't be null\n");
You may use the following convenience macros to determine the boolean
status of the flags value:
IS_NOT_NULL(flags) | True if this field is defined as NOT NULL
|
IS_PRI_KEY(flags) | True if this field is a primary key |
IS_BLOB(flags) | True if this field is a BLOB or TEXT (deprecated; test field->type instead)
|
unsigned int decimals
The functions available in the C API are listed below and are described in greater detail in the next section. See section 22.4 C API Function Descriptions.
| mysql_affected_rows() |
Returns the number of rows affected by the last UPDATE,
DELETE, or INSERT query.
|
| mysql_close() | Closes a server connection. |
| mysql_connect() |
Connects to a MySQL server. This function is deprecated; use
mysql_real_connect() instead.
|
| mysql_change_user() | Changes user and database on an open connection. |
mysql_character_set_name() | Returns the name of the default character set for the connection. |
| mysql_create_db() |
Creates a database. This function is deprecated; use the SQL command
CREATE DATABASE instead.
|
| mysql_data_seek() | Seeks to an arbitrary row in a query result set. |
| mysql_debug() |
Does a DBUG_PUSH with the given string.
|
| mysql_drop_db() |
Drops a database. This function is deprecated; use the SQL command
DROP DATABASE instead.
|
| mysql_dump_debug_info() | Makes the server write debug information to the log. |
| mysql_eof() |
Determines whether or not the last row of a result set has been read.
This function is deprecated; mysql_errno() or mysql_error()
may be used instead.
|
| mysql_errno() | Returns the error number for the most recently invoked MySQL function. |
| mysql_error() | Returns the error message for the most recently invoked MySQL function. |
| mysql_real_escape_string() | Escapes special characters in a string for use in a SQL statement taking into account the current charset of the connection. |
| mysql_escape_string() | Escapes special characters in a string for use in a SQL statement. |
| mysql_fetch_field() | Returns the type of the next table field. |
| mysql_fetch_field_direct() | Returns the type of a table field, given a field number. |
| mysql_fetch_fields() | Returns an array of all field structures. |
| mysql_fetch_lengths() | Returns the lengths of all columns in the current row. |
| mysql_fetch_row() | Fetches the next row from the result set. |
| mysql_field_seek() | Puts the column cursor on a specified column. |
| mysql_field_count() | Returns the number of result columns for the most recent query. |
| mysql_field_tell() |
Returns the position of the field cursor used for the last
mysql_fetch_field().
|
| mysql_free_result() | Frees memory used by a result set. |
| mysql_get_client_info() | Returns client version information. |
| mysql_get_host_info() | Returns a string describing the connection. |
| mysql_get_proto_info() | Returns the protocol version used by the connection. |
| mysql_get_server_info() | Returns the server version number. |
| mysql_info() | Returns information about the most recently executed query. |
| mysql_init() |
Gets or initializes a MYSQL structure.
|
| mysql_insert_id() |
Returns the ID generated for an AUTO_INCREMENT column by the previous
query.
|
| mysql_kill() | Kills a given thread. |
| mysql_list_dbs() | Returns database names matching a simple regular expression. |
| mysql_list_fields() | Returns field names matching a simple regular expression. |
| mysql_list_processes() | Returns a list of the current server threads. |
| mysql_list_tables() | Returns table names matching a simple regular expression. |
| mysql_num_fields() | Returns the number of columns in a result set. |
| mysql_num_rows() | Returns the number of rows in a result set. |
| mysql_options() |
Sets connect options for mysql_connect().
|
| mysql_ping() | Checks whether or not the connection to the server is working, reconnecting as necessary. |
| mysql_query() | Executes a SQL query specified as a null-terminated string. |
| mysql_real_connect() | Connects to a MySQL server. |
| mysql_real_query() | Executes a SQL query specified as a counted string. |
| mysql_reload() | Tells the server to reload the grant tables. |
| mysql_row_seek() |
Seeks to a row in a result set, using value returned from
mysql_row_tell().
|
| mysql_row_tell() | Returns the row cursor position. |
| mysql_select_db() | Selects a database. |
| mysql_shutdown() | Shuts down the database server. |
| mysql_start_slave() | Starts slave replication thread. |
| mysql_stat() | Returns the server status as a string. |
| mysql_store_result() | Retrieves a complete result set to the client. |
| mysql_stop_slave() | Stops slave replication thread. |
| mysql_thread_id() | Returns the current thread ID. |
| mysql_thread_save() | Returns 1 if the clients are compiled as threadsafe. |
| mysql_use_result() | Initiates a row-by-row result set retrieval. |
To connect to the server, call mysql_init() to initialize a
connection handler, then call mysql_real_connect() with that
handler (along with other information such as the hostname, user name,
and password). Upon connection, mysql_real_connect() sets the
reconnect flag (part of the MYSQL structure) to a value of
1. This flag indicates, in the event that a query cannot be
performed because of a lost connection, to try reconnecting to the
server before giving up. When you are done with the connection, call
mysql_close() to terminate it.
While a connection is active, the client may send SQL queries to the server
using mysql_query() or mysql_real_query(). The difference
between the two is that mysql_query() expects the query to be
specified as a null-terminated string whereas mysql_real_query()
expects a counted string. If the string contains binary data (which may
include null bytes), you must use mysql_real_query().
For each non-SELECT query (for example, INSERT, UPDATE,
DELETE), you can find out how many rows were affected (changed)
by calling mysql_affected_rows().
For SELECT queries, you retrieve the selected rows as a result set.
(Note that some statements are SELECT-like in that they return rows.
These include SHOW, DESCRIBE, and EXPLAIN. They should
be treated the same way as SELECT statements.)
There are two ways for a client to process result sets. One way is to
retrieve the entire result set all at once by calling
mysql_store_result(). This function acquires from the server all the
rows returned by the query and stores them in the client. The second way is
for the client to initiate a row-by-row result set retrieval by calling
mysql_use_result(). This function initializes the retrieval, but does
not actually get any rows from the server.
In both cases, you access rows by calling mysql_fetch_row(). With
mysql_store_result(), mysql_fetch_row() accesses rows that have
already been fetched from the server. With mysql_use_result(),
mysql_fetch_row() actually retrieves the row from the server.
Information about the size of the data in each row is available by
calling mysql_fetch_lengths().
After you are done with a result set, call mysql_free_result()
to free the memory used for it.
The two retrieval mechanisms are complementary. Client programs should
choose the approach that is most appropriate for their requirements.
In practice, clients tend to use mysql_store_result() more
commonly.
An advantage of mysql_store_result() is that because the rows have all
been fetched to the client, you not only can access rows sequentially, you
can move back and forth in the result set using mysql_data_seek() or
mysql_row_seek() to change the current row position within the result
set. You can also find out how many rows there are by calling
mysql_num_rows(). On the other hand, the memory requirements for
mysql_store_result() may be very high for large result sets and you
are more likely to encounter out-of-memory conditions.
An advantage of mysql_use_result() is that the client requires less
memory for the result set because it maintains only one row at a time (and
because there is less allocation overhead, mysql_use_result() can be
faster). Disadvantages are that you must process each row quickly to avoid
tying up the server, you don't have random access to rows within the result
set (you can only access rows sequentially), and you don't know how many rows
are in the result set until you have retrieved them all. Furthermore, you
must retrieve all the rows even if you determine in mid-retrieval that
you've found the information you were looking for.
The API makes it possible for clients to respond appropriately to
queries (retrieving rows only as necessary) without knowing whether or
not the query is a SELECT. You can do this by calling
mysql_store_result() after each mysql_query() (or
mysql_real_query()). If the result set call succeeds, the query
was a SELECT and you can read the rows. If the result set call
fails, call mysql_field_count() to determine whether or not a
result was actually to be expected. If mysql_field_count()
returns zero, the query returned no data (indicating that it was an
INSERT, UPDATE, DELETE, etc.), and was not
expected to return rows. If mysql_field_count() is non-zero, the
query should have returned rows, but didn't. This indicates that the
query was a SELECT that failed. See the description for
mysql_field_count() for an example of how this can be done.
Both mysql_store_result() and mysql_use_result() allow you to
obtain information about the fields that make up the result set (the number
of fields, their names and types, etc.). You can access field information
sequentially within the row by calling mysql_fetch_field() repeatedly,
or by field number within the row by calling
mysql_fetch_field_direct(). The current field cursor position may be
changed by calling mysql_field_seek(). Setting the field cursor
affects subsequent calls to mysql_fetch_field(). You can also get
information for fields all at once by calling mysql_fetch_fields().
For detecting and reporting errors, MySQL provides access to error
information by means of the mysql_errno() and mysql_error()
functions. These return the error code or error message for the most
recently invoked function that can succeed or fail, allowing you to determine
when an error occurred and what it was.
In the descriptions below, a parameter or return value of NULL means
NULL in the sense of the C programming language, not a
MySQL NULL value.
Functions that return a value generally return a pointer or an integer.
Unless specified otherwise, functions returning a pointer return a
non-NULL value to indicate success or a NULL value to indicate
an error, and functions returning an integer return zero to indicate success
or non-zero to indicate an error. Note that ``non-zero'' means just that.
Unless the function description says otherwise, do not test against a value
other than zero:
if (result) /* correct */
... error ...
if (result < 0) /* incorrect */
... error ...
if (result == -1) /* incorrect */
... error ...
When a function returns an error, the Errors subsection of the
function description lists the possible types of errors. You can
find out which of these occurred by calling mysql_errno().
A string representation of the error may be obtained by calling
mysql_error().
mysql_affected_rows()
my_ulonglong mysql_affected_rows(MYSQL *mysql)
Returns the number of rows affected (changed) by the last UPDATE,
DELETE or INSERT query. May be called immediately after
mysql_query() for UPDATE, DELETE, or INSERT
statements. For SELECT statements, mysql_affected_rows()
works like mysql_num_rows().
mysql_affected_rows() is currently implemented as a macro.
An integer greater than zero indicates the number of rows affected or
retrieved. Zero indicates that no records matched the WHERE clause in
the query or that no query has yet been executed. -1 indicates that the
query returned an error or that, for a SELECT query,
mysql_affected_rows() was called prior to calling
mysql_store_result().
None.
mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%d products updated",mysql_affected_rows(&mysql));
mysql_close()
void mysql_close(MYSQL *mysql)
Closes a previously opened connection. mysql_close() also deallocates
the connection handle pointed to by mysql if the handle was allocated
automatically by mysql_init() or mysql_connect().
None.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_connect()
MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)
This function is deprecated. It is preferable to use
mysql_real_connect() instead.
mysql_connect() attempts to establish a connection to a MySQL
database engine running on host. mysql_connect() must complete
successfully before you can execute any of the other API functions, with the
exception of mysql_get_client_info().
The meanings of the parameters are the same as for the corresponding
parameters for mysql_real_connect() with the difference that the
connection parameter may be NULL. In this case the C API
allocates memory for the connection structure automatically and frees it
when you call mysql_close(). The disadvantage of this approach is
that you can't retrieve an error message if the connection fails. (To
get error information from mysql_errno() or mysql_error(),
you must provide a valid MYSQL pointer.)
Same as for mysql_real_connect().
Same as for mysql_real_connect().
mysql_change_user()
my_bool mysql_change_user(MYSQL *mysql, const char *user, const
char *password, const char *db)
Changes the user and causes the database specified by db to
become the default (current) database on the connection specified by
mysql. In subsequent queries, this database is the default for
table references that do not include an explicit database specifier.
This function was introduced in MySQL Version 3.23.3.
mysql_change_user() fails unless the connected user can be
authenticated or if he doesn't have permission to use the database. In
this case the user and database are not changed
The db parameter may be set to NULL if you don't want to have a
default database.
Zero for success. Non-zero if an error occurred.
The same that you can get from mysql_real_connect().
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
ER_UNKNOWN_COM_ERROR
ER_ACCESS_DENIED_ERROR
ER_BAD_DB_ERROR
ER_DBACCESS_DENIED_ERROR
ER_WRONG_DB_NAME
if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
fprintf(stderr, "Failed to change user. Error: %s\n",
mysql_error(&mysql));
}
mysql_character_set_name()
const char *mysql_character_set_name(MYSQL *mysql)
Returns the default character set for the current connection.
The default character set
None.
mysql_create_db()
int mysql_create_db(MYSQL *mysql, const char *db)
Creates the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL CREATE DATABASE statement instead.
Zero if the database was created successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_create_db(&mysql, "my_database"))
{
fprintf(stderr, "Failed to create new database. Error: %s\n",
mysql_error(&mysql));
}
mysql_data_seek()
void mysql_data_seek(MYSQL_RES *result, unsigned long long offset)
Seeks to an arbitrary row in a query result set. This requires that the
result set structure contains the entire result of the query, so
mysql_data_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value in the range from 0 to
mysql_num_rows(result)-1.
None.
None.
mysql_debug()
void mysql_debug(char *debug)
Does a DBUG_PUSH with the given string. mysql_debug() uses the
Fred Fish debug library. To use this function, you must compile the client
library to support debugging.
See section H.1 Debugging a MySQL server. See section H.2 Debugging a MySQL client.
None.
None.
The call shown below causes the client library to generate a trace file in `/tmp/client.trace' on the client machine:
mysql_debug("d:t:O,/tmp/client.trace");
mysql_drop_db()
int mysql_drop_db(MYSQL *mysql, const char *db)
Drops the database named by the db parameter.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL DROP DATABASE statement instead.
Zero if the database was dropped successfully. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
if(mysql_drop_db(&mysql, "my_database"))
fprintf(stderr, "Failed to drop the database: Error: %s\n",
mysql_error(&mysql));
mysql_dump_debug_info()
int mysql_dump_debug_info(MYSQL *mysql)
Instructs the server to write some debug information to the log. The connected user must have the process privilege for this to work.
Zero if the command was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_eof()
my_bool mysql_eof(MYSQL_RES *result)
This function is deprecated. mysql_errno() or mysql_error()
may be used instead.
mysql_eof() determines whether or not the last row of a result
set has been read.
If you acquire a result set from a successful call to
mysql_store_result(), the client receives the entire set in one
operation. In this case, a NULL return from mysql_fetch_row()
always means the end of the result set has been reached and it is
unnecessary to call mysql_eof().
On the other hand, if you use mysql_use_result() to initiate a result
set retrieval, the rows of the set are obtained from the server one by one as
you call mysql_fetch_row() repeatedly. Because an error may occur on
the connection during this process, a NULL return value from
mysql_fetch_row() does not necessarily mean the end of the result set
was reached normally. In this case, you can use mysql_eof() to
determine what happened. mysql_eof() returns a non-zero value if the
end of the result set was reached and zero if an error occurred.
Historically, mysql_eof() predates the standard MySQL error
functions mysql_errno() and mysql_error(). Because those error
functions provide the same information, their use is preferred over
mysql_eof(), which is now deprecated. (In fact, they provide more
information, because mysql_eof() returns only a boolean value whereas
the error functions indicate a reason for the error when one occurs.)
Zero if no error occurred. Non-zero if the end of the result set has been reached.
None.
The following example shows how you might use mysql_eof():
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(!mysql_eof(result)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
However, you can achieve the same effect with the standard MySQL error functions:
mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
// do something with data
}
if(mysql_errno(&mysql)) // mysql_fetch_row() failed due to an error
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
mysql_errno()
unsigned int mysql_errno(MYSQL *mysql)
For the connection specified by mysql, mysql_errno() returns
the error code for the most recently invoked API function that can succeed
or fail. A return value of zero means that no error occurred. Client error
message numbers are listed in the MySQL `errmsg.h' header file.
Server error message numbers are listed in `mysqld_error.h'. In the
MySQL source distribution you can find a complete list of
error messages and error numbers in the file `Docs/mysqld_error.txt'.
An error code value. Zero if no error occurred.
None.
mysql_error()
char *mysql_error(MYSQL *mysql)
For the connection specified by mysql, mysql_error() returns
the error message for the most recently invoked API function that can succeed
or fail. An empty string ("") is returned if no error occurred.
This means the following two tests are equivalent:
if(mysql_errno(&mysql))
{
// an error occurred
}
if(mysql_error(&mysql)[0] != '\0')
{
// an error occurred
}
The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages. See section 10.1 What Languages Are Supported by MySQL?.
A character string that describes the error. An empty string if no error occurred.
None.
mysql_escape_string()
You should use mysql_real_escape_string() instead!
This is identical to mysql_real_escape_string() except that it takes
the connection as the first argument. mysql_real_escape_string()
will escape the string according to the current character set while mysql_escape_string()
does not respect the current charset setting.
mysql_fetch_field()
MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)
Returns the definition of one column of a result set as a MYSQL_FIELD
structure. Call this function repeatedly to retrieve information about all
columns in the result set. mysql_fetch_field() returns NULL
when no more fields are left.
mysql_fetch_field() is reset to return information about the first
field each time you execute a new SELECT query. The field returned by
mysql_fetch_field() is also affected by calls to
mysql_field_seek().
If you've called mysql_query() to perform a SELECT on a table
but have not called mysql_store_result(), MySQL returns the
default blob length (8K bytes) if you call mysql_fetch_field() to ask
for the length of a BLOB field. (The 8K size is chosen because
MySQL doesn't know the maximum length for the BLOB. This
should be made configurable sometime.) Once you've retrieved the result set,
field->max_length contains the length of the largest value for this
column in the specific query.
The MYSQL_FIELD structure for the current column. NULL
if no columns are left.
None.
MYSQL_FIELD *field;
while((field = mysql_fetch_field(result)))
{
printf("field name %s\n", field->name);
}
mysql_fetch_fields()
MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)
Returns an array of all MYSQL_FIELD structures for a result set.
Each structure provides the field definition for one column of the result
set.
An array of MYSQL_FIELD structures for all columns of a result set.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;
num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
printf("Field %u is %s\n", i, fields[i].name);
}
mysql_fetch_field_direct()
MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)
Given a field number fieldnr for a column within a result set, returns
that column's field definition as a MYSQL_FIELD structure. You may use
this function to retrieve the definition for an arbitrary column. The value
of fieldnr should be in the range from 0 to
mysql_num_fields(result)-1.
The MYSQL_FIELD structure for the specified column.
None.
unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;
num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
field = mysql_fetch_field_direct(result, i);
printf("Field %u is %s\n", i, field->name);
}
mysql_fetch_lengths()
unsigned long *mysql_fetch_lengths(MYSQL_RES *result)
Returns the lengths of the columns of the current row within a result set.
If you plan to copy field values, this length information is also useful for
optimization, because you can avoid calling strlen(). In addition, if
the result set contains binary data, you must use this function to
determine the size of the data, because strlen() returns incorrect
results for any field containing null characters.
The length for empty columns and for columns containing NULL values is
zero. To see how to distinguish these two cases, see the description for
mysql_fetch_row().
An array of unsigned long integers representing the size of each column (not
including any terminating null characters).
NULL if an error occurred.
mysql_fetch_lengths() is valid only for the current row of the result
set. It returns NULL if you call it before calling
mysql_fetch_row() or after retrieving all rows in the result.
MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;
row = mysql_fetch_row(result);
if (row)
{
num_fields = mysql_num_fields(result);
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("Column %u is %lu bytes in length.\n", i, lengths[i]);
}
}
mysql_fetch_row()
MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)
Retrieves the next row of a result set. When used after
mysql_store_result(), mysql_fetch_row() returns NULL
when there are no more rows to retrieve. When used after
mysql_use_result(), mysql_fetch_row() returns NULL when
there are no more rows to retrieve or if an error occurred.
The number of values in the row is given by mysql_num_fields(result).
If row holds the return value from a call to mysql_fetch_row(),
pointers to the values are accessed as row[0] to
row[mysql_num_fields(result)-1]. NULL values in the row are
indicated by NULL pointers.
The lengths of the field values in the row may be obtained by calling
mysql_fetch_lengths(). Empty fields and fields containing
NULL both have length 0; you can distinguish these by checking
the pointer for the field value. If the pointer is NULL, the field
is NULL; otherwise the field is empty.
A MYSQL_ROW structure for the next row. NULL if
there are no more rows to retrieve or if an error occurred.
CR_SERVER_LOST
CR_UNKNOWN_ERROR
MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;
num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
unsigned long *lengths;
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("[%.*s] ", (int) lengths[i], row[i] ? row[i] : "NULL");
}
printf("\n");
}
mysql_field_count()
unsigned int mysql_field_count(MYSQL *mysql)
If you are using a version of MySQL earlier than Version 3.22.24, you
should use unsigned int mysql_num_fields(MYSQL *mysql) instead.
Returns the number of columns for the most recent query on the connection.
The normal use of this function is when mysql_store_result()
returned NULL (and thus you have no result set pointer).
In this case, you can call mysql_field_count() to
determine whether or not mysql_store_result() should have produced a
non-empty result. This allows the client program to take proper action
without knowing whether or not the query was a SELECT (or
SELECT-like) statement. The example shown below illustrates how this
may be done.
See section 22.4.53 Why Is It that After mysql_query() Returns Success, mysql_store_result() Sometimes Returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if(mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
else // mysql_store_result() should have returned data
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
}
}
An alternative is to replace the mysql_field_count(&mysql) call with
mysql_errno(&mysql). In this case, you are checking directly for an
error from mysql_store_result() rather than inferring from the value
of mysql_field_count() whether or not the statement was a
SELECT.
mysql_field_seek()
MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)
Sets the field cursor to the given offset. The next call to
mysql_fetch_field() will retrieve the field definition of the column
associated with that offset.
To seek to the beginning of a row, pass an offset value of zero.
The previous value of the field cursor.
None.
mysql_field_tell()
MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)
Returns the position of the field cursor used for the last
mysql_fetch_field(). This value can be used as an argument to
mysql_field_seek().
The current offset of the field cursor.
None.
mysql_free_result()
void mysql_free_result(MYSQL_RES *result)
Frees the memory allocated for a result set by mysql_store_result(),
mysql_use_result(), mysql_list_dbs(), etc. When you are done
with a result set, you must free the memory it uses by calling
mysql_free_result().
None.
None.
mysql_get_client_info()
char *mysql_get_client_info(void)
Returns a string that represents the client library version.
A character string that represents the MySQL client library version.
None.
mysql_get_host_info()
char *mysql_get_host_info(MYSQL *mysql)
Returns a string describing the type of connection in use, including the server host name.
A character string representing the server host name and the connection type.
None.
mysql_get_proto_info()
unsigned int mysql_get_proto_info(MYSQL *mysql)
Returns the protocol version used by current connection.
An unsigned integer representing the protocol version used by the current connection.
None.
mysql_get_server_info()
char *mysql_get_server_info(MYSQL *mysql)
Returns a string that represents the server version number.
A character string that represents the server version number.
None.
mysql_info()
char *mysql_info(MYSQL *mysql)
Retrieves a string providing information about the most recently executed
query, but only for the statements listed below. For other statements,
mysql_info() returns NULL. The format of the string varies
depending on the type of query, as described below. The numbers are
illustrative only; the string will contain values appropriate for the query.
INSERT INTO ... SELECT ...
Records: 100 Duplicates: 0 Warnings: 0
INSERT INTO ... VALUES (...),(...),(...)...
Records: 3 Duplicates: 0 Warnings: 0
LOAD DATA INFILE ...
Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
ALTER TABLE
Records: 3 Duplicates: 0 Warnings: 0
UPDATE
Rows matched: 40 Changed: 40 Warnings: 0
Note that mysql_info() returns a non-NULL value for the
INSERT ... VALUES statement only if multiple value lists are
specified in the statement.
A character string representing additional information about the most
recently executed query. NULL if no information is available for the
query.
None.
mysql_init()
MYSQL *mysql_init(MYSQL *mysql)
Allocates or initializes a MYSQL object suitable for
mysql_real_connect(). If mysql is a NULL pointer, the
function allocates, initializes, and returns a new object. Otherwise the
object is initialized and the address of the object is returned. If
mysql_init() allocates a new object, it will be freed when
mysql_close() is called to close the connection.
An initialized MYSQL* handle. NULL if there was
insufficient memory to allocate a new object.
In case of insufficient memory, NULL is returned.
mysql_insert_id()
my_ulonglong mysql_insert_id(MYSQL *mysql)
Returns the ID generated for an AUTO_INCREMENT column by the previous
query. Use this function after you have performed an INSERT query
into a table that contains an AUTO_INCREMENT field.
Note that mysql_insert_id() returns 0 if the previous query
does not generate an AUTO_INCREMENT value. If you need to save
the value for later, be sure to call mysql_insert_id() immediately
after the query that generates the value.
Also note that the value of the SQL LAST_INSERT_ID() function always
contains the most recently generated AUTO_INCREMENT value, and is
not reset between queries because the value of that function is maintained
in the server.
The value of the AUTO_INCREMENT field that was updated by the previous
query. Returns zero if there was no previous query on the connection or if
the query did not update an AUTO_INCREMENT value.
None.
mysql_kill()
int mysql_kill(MYSQL *mysql, unsigned long pid)
Asks the server to kill the thread specified by pid.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_dbs()
MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)
Returns a result set consisting of database names on the server that match
the simple regular expression specified by the wild parameter.
wild may contain the wild-card characters `%' or `_', or may
be a NULL pointer to match all databases. Calling
mysql_list_dbs() is similar to executing the query SHOW
databases [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_fields()
MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)
Returns a result set consisting of field names in the given table that match
the simple regular expression specified by the wild parameter.
wild may contain the wild-card characters `%' or `_', or may
be a NULL pointer to match all fields. Calling
mysql_list_fields() is similar to executing the query SHOW
COLUMNS FROM tbl_name [LIKE wild].
Note that it's recommended that you use SHOW COLUMNS FROM tbl_name
instead of mysql_list_fields().
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_processes()
MYSQL_RES *mysql_list_processes(MYSQL *mysql)
Returns a result set describing the current server threads. This is the same
kind of information as that reported by mysqladmin processlist or
a SHOW PROCESSLIST query.
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_list_tables()
MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)
Returns a result set consisting of table names in the current database that
match the simple regular expression specified by the wild parameter.
wild may contain the wild-card characters `%' or `_', or may
be a NULL pointer to match all tables. Calling
mysql_list_tables() is similar to executing the query SHOW
tables [LIKE wild].
You must free the result set with mysql_free_result().
A MYSQL_RES result set for success. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_num_fields()
unsigned int mysql_num_fields(MYSQL_RES *result)
or
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a
MYSQL* argument, you must use
unsigned int mysql_field_count(MYSQL *mysql) instead.
Returns the number of columns in a result set.
Note that you can get the number of columns either from a pointer to a result
set or to a connection handle. You would use the connection handle if
mysql_store_result() or mysql_use_result() returned
NULL (and thus you have no result set pointer). In this case, you can
call mysql_field_count() to determine whether or not
mysql_store_result() should have produced a non-empty result. This
allows the client program to take proper action without knowing whether or
not the query was a SELECT (or SELECT-like) statement. The
example shown below illustrates how this may be done.
See section 22.4.53 Why Is It that After mysql_query() Returns Success, mysql_store_result() Sometimes Returns NULL?.
An unsigned integer representing the number of fields in a result set.
None.
MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;
if (mysql_query(&mysql,query_string))
{
// error
}
else // query succeeded, process any data returned by it
{
result = mysql_store_result(&mysql);
if (result) // there are rows
{
num_fields = mysql_num_fields(result);
// retrieve rows, then call mysql_free_result(result)
}
else // mysql_store_result() returned nothing; should it have?
{
if (mysql_errno(&mysql))
{
fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}
else if (mysql_field_count(&mysql) == 0)
{
// query does not return data
// (it was not a SELECT)
num_rows = mysql_affected_rows(&mysql);
}
}
}
An alternative (if you KNOW that your query should have returned a result set)
is to replace the mysql_errno(&mysql) call with a check if
mysql_field_count(&mysql) is = 0. This will only happen if something
went wrong.
mysql_num_rows()
my_ulonglong mysql_num_rows(MYSQL_RES *result)
Returns the number of rows in the result set.
The use of mysql_num_rows() depends on whether you use
mysql_store_result() or mysql_use_result() to return the result
set. If you use mysql_store_result(), mysql_num_rows() may be
called immediately. If you use mysql_use_result(),
mysql_num_rows() will not return the correct value until all the rows
in the result set have been retrieved.
The number of rows in the result set.
None.
mysql_options()
int mysql_options(MYSQL *mysql, enum mysql_option option, const char *arg)
Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.
mysql_options() should be called after mysql_init() and before
mysql_connect() or mysql_real_connect().
The option argument is the option that you want to set; the arg
argument is the value for the option. If the option is an integer, then
arg should point to the value of the integer.
Possible options values:
| Option | Argument type | Function |
MYSQL_OPT_CONNECT_TIMEOUT | unsigned int * | Connect timeout in seconds. |
MYSQL_OPT_COMPRESS | Not used | Use the compressed client/server protocol. |
MYSQL_OPT_NAMED_PIPE | Not used | Use named pipes to connect to a MySQL server on NT. |
MYSQL_INIT_COMMAND | char * | Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting. |
MYSQL_READ_DEFAULT_FILE | char * | Read options from the named option file instead of from `my.cnf'. |
MYSQL_READ_DEFAULT_GROUP | char * | Read options from the named group from `my.cnf' or the file specified with MYSQL_READ_DEFAULT_FILE.
|
Note that the group client is always read if you use
MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.
The specified group in the option file may contain the following options:
connect_timeout | Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server. |
compress | Use the compressed client/server protocol. |
database | Connect to this database if no database was specified in the connect command. |
debug | Debug options. |
host | Default host name. |
init-command | Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting. |
interactive-timeout | Same as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See section 22.4.41 mysql_real_connect().
|
password | Default password. |
pipe | Use named pipes to connect to a MySQL server on NT. |
port | Default port number. |
return-found-rows | Tell mysql_info() to return found rows instead of updated rows when using UPDATE.
|
socket | Default socket number. |
user | Default user. |
Note that timeout has been replaced by connect_timeout, but
timeout will still work for a while.
For more information about option files, see section 4.16.5 Option Files.
Zero for success. Non-zero if you used an unknown option.
MYSQL mysql;
mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
The above requests the client to use the compressed client/server protocol and
read the additional options from the odbc section in the my.cnf
file.
mysql_ping()
int mysql_ping(MYSQL *mysql)
Checks whether or not the connection to the server is working. If it has gone down, an automatic reconnection is attempted.
This function can be used by clients that remain idle for a long while, to check whether or not the server has closed the connection and reconnect if necessary.
Zero if the server is alive. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_UNKNOWN_ERROR
mysql_query()
int mysql_query(MYSQL *mysql, const char *query)
Executes the SQL query pointed to by the null-terminated string query.
The query must consist of a single SQL statement. You should not add
a terminating semicolon (`;') or \g to the statement.
mysql_query() cannot be used for queries that contain binary data; you
should use mysql_real_query() instead. (Binary data may contain the
`\0' character, which mysql_query() interprets as the end of the
query string.)
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this.
See section 22.4.20 mysql_field_count().
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_real_connect()
MYSQL *mysql_real_connect(MYSQL *mysql, const char *host,
const char *user, const char *passwd, const char *db,
unsigned int port, const char *unix_socket,
unsigned int client_flag)
mysql_real_connect() attempts to establish a connection to a
MySQL database engine running on host.
mysql_real_connect() must complete successfully before you can execute
any of the other API functions, with the exception of
mysql_get_client_info().
The parameters are specified as follows:
MYSQL
structure. Before calling mysql_real_connect() you must call
mysql_init() to initialize the MYSQL structure. See the
example below.
host may be either a hostname or an IP address. If
host is NULL or the string "localhost", a connection to
the local host is assumed. If the OS supports sockets (Unix) or named pipes
(Windows), they are used instead of TCP/IP to connect to the server.
user parameter contains the user's MySQL login ID. If
user is NULL, the current user is assumed. Under Unix, this is
the current login name. Under Windows ODBC, the current user name must be
specified explicitly.
See section 18.2 How to Fill in the Various Fields in the ODBC Administrator Program.
passwd parameter contains the password for user. If
passwd is NULL, only entries in the user table for the
user that have a blank password field will be checked for a match. This
allows the database administrator to set up the MySQL privilege
system in such a way that users get different privileges depending on whether
or not they have specified a password.
NOTE: Do not attempt to encrypt the password before calling
mysql_real_connect(); password encryption is handled automatically by
the client API.
db is the database name.
If db is not NULL, the connection will set the default
database to this value.
port is not 0, the value will be used as the port number
for the TCP/IP connection. Note that the host parameter
determines the type of the connection.
unix_socket is not NULL, the string specifies the
socket or named pipe that should be used. Note that the host
parameter determines the type of the connection.
client_flag is usually 0, but can be set to a combination
of the following flags in very special circumstances:
| Flag name | Flag meaning
mysqld to be more ODBC-friendly.
|
CLIENT_COMPRESS | Use compression protocol. |
CLIENT_FOUND_ROWS | Return the number of found (matched) rows, not the number of affected rows. |
CLIENT_IGNORE_SPACE $tab Allow spaces after function names. Makes all functions names reserved words.
| |
CLIENT_INTERACTIVE | Allow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection.
|
CLIENT_NO_SCHEMA | Don't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.
|
CLIENT_ODBC | The client is an ODBC client. This changes |
CLIENT_SSL | Use SSL (encrypted protocol). |
A MYSQL* connection handle if the connection was successful,
NULL if the connection was unsuccessful. For a successful connection,
the return value is the same as the value of the first parameter, unless you
pass NULL for that parameter.
CR_CONN_HOST_ERROR
CR_CONNECTION_ERROR
CR_IPSOCK_ERROR
CR_OUT_OF_MEMORY
CR_SOCKET_CREATE_ERROR
CR_UNKNOWN_HOST
CR_VERSION_ERROR
--old-protocol option.
CR_NAMEDPIPEOPEN_ERROR
CR_NAMEDPIPEWAIT_ERROR
CR_NAMEDPIPESETSTATE_ERROR
CR_SERVER_LOST
connect_timeout > 0 and it took longer then connect_timeout
seconds to connect to the server or if the server died while executing the
init-command.
MYSQL mysql;
mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
fprintf(stderr, "Failed to connect to database: Error: %s\n",
mysql_error(&mysql));
}
By using mysql_options() the MySQL library will read the
[client] and your_prog_name sections in the my.cnf
file which will ensure that your program will work, even if someone has
set up MySQL in some non-standard way.
Note that upon connection, mysql_real_connect() sets the reconnect
flag (part of the MYSQL structure) to a value of 1. This flag indicates,
in the event that a query cannot be performed because of a lost connection, to
try reconnecting to the server before giving up.
mysql_real_escape_string()
unsigned int mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned int length)
Encodes the string in from to an escaped SQL string, taking into
account the current charset of the connection, that can be sent to the
server in a SQL statement, places the result in to, and adds a
terminating null byte. Characters encoded are NUL (ASCII 0),
`\n', `\r', `\', `'', `"', and Control-Z
(see section 7.1 Literals: How to Write Strings and Numbers).
The string pointed to by from must be length bytes long. You
must allocate the to buffer to be at least length*2+1 bytes
long. (In the worse case, each character may need to be encoded as using two
bytes, and you need room for the terminating null byte.) When
mysql_escape_string() returns, the contents of to will be a
null-terminated string. The return value is the length of the encoded
string, not including the terminating null character.
char query[1000],*end;
end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';
if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
fprintf(stderr, "Failed to insert row, Error: %s\n",
mysql_error(&mysql));
}
The strmov() function used in the example is included in the
mysqlclient library and works like strcpy() but returns a
pointer to the terminating null of the first parameter.
The length of the value placed into to, not including the
terminating null character.
None.
mysql_real_query()
int mysql_real_query(MYSQL *mysql, const char *query, unsigned int length)
Executes the SQL query pointed to by query, which should be a string
length bytes long. The query must consist of a single SQL statement.
You should not add a terminating semicolon (`;') or \g to the
statement.
You must use mysql_real_query() rather than
mysql_query() for queries that contain binary data, because binary data
may contain the `\0' character. In addition, mysql_real_query()
is faster than mysql_query() because it does not call strlen() on
the query string.
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this.
See section 22.4.20 mysql_field_count().
Zero if the query was successful. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_reload()
int mysql_reload(MYSQL *mysql)
Asks the MySQL server to reload the grant tables. The connected user must have the reload privilege.
This function is deprecated. It is preferable to use mysql_query()
to issue a SQL FLUSH PRIVILEGES statement instead.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_row_seek()
MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)
Sets the row cursor to an arbitrary row in a query result set. This requires
that the result set structure contains the entire result of the query, so
mysql_row_seek() may be used in conjunction only with
mysql_store_result(), not with mysql_use_result().
The offset should be a value returned from a call to mysql_row_tell()
or to mysql_row_seek(). This value is not simply a row number; if you
want to seek to a row within a result set using a row number, use
mysql_data_seek() instead.
The previous value of the row cursor. This value may be passed to a
subsequent call to mysql_row_seek().
None.
mysql_row_tell()
MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)
Returns the current position of the row cursor for the last
mysql_fetch_row(). This value can be used as an argument to
mysql_row_seek().
You should use mysql_row_tell() only after mysql_store_result(),
not after mysql_use_result().
The current offset of the row cursor.
None.
mysql_select_db()
int mysql_select_db(MYSQL *mysql, const char *db)
Causes the database specified by db to become the default (current)
database on the connection specified by mysql. In subsequent queries,
this database is the default for table references that do not include an
explicit database specifier.
mysql_select_db() fails unless the connected user can be authenticated
as having permission to use the database.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_shutdown()
int mysql_shutdown(MYSQL *mysql)
Asks the database server to shut down. The connected user must have shutdown privileges.
Zero for success. Non-zero if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_stat()
char *mysql_stat(MYSQL *mysql)
Returns a character string containing information similar to that provided by
the mysqladmin status command. This includes uptime in seconds and
the number of running threads, questions, reloads, and open tables.
A character string describing the server status. NULL if an
error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_store_result()
MYSQL_RES *mysql_store_result(MYSQL *mysql)
You must call mysql_store_result() or mysql_use_result()
for every query that successfully retrieves data (SELECT,
SHOW, DESCRIBE, EXPLAIN).
If you want to know if the query should return a result set or not, you can
use mysql_field_count() to check for this.
See section 22.4.20 mysql_field_count().
mysql_store_result() reads the entire result of a query to the client,
allocates a MYSQL_RES structure, and places the result into this
structure.
mysql_store_results() returns a null pointer if the query didn't return
a result set (if the query was, for example, an INSERT statement).
mysql_store_results() also returns a null pointer if reading of the
result set failed. You can check if you got an error by checking if
mysql_error() doesn't return a null pointer, if
mysql_errno() returns <> 0, or if mysql_field_count()
returns <> 0.
An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)
Once you have called mysql_store_result() and got a result back
that isn't a null pointer, you may call mysql_num_rows() to find
out how many rows are in the result set.
You can call mysql_fetch_row() to fetch rows from the result set,
or mysql_row_seek() and mysql_row_tell() to obtain or
set the current row position within the result set.
You must call mysql_free_result() once you are done with the result
set.
See section 22.4.53 Why Is It that After mysql_query() Returns Success, mysql_store_result() Sometimes Returns NULL?.
A MYSQL_RES result structure with the results. NULL if
an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_thread_id()
unsigned long mysql_thread_id(MYSQL *mysql)
Returns the thread ID of the current connection. This value can be used as
an argument to mysql_kill() to kill the thread.
If the connection is lost and you reconnect with mysql_ping(), the
thread ID will change. This means you should not get the thread ID and store
it for later. You should get it when you need it.
The thread ID of the current connection.
None.
mysql_use_result()
MYSQL_RES *mysql_use_result(MYSQL *mysql)
You must call mysql_store_result() or mysql_use_result() for
every query that successfully retrieves data (SELECT, SHOW,
DESCRIBE, EXPLAIN).
mysql_use_result() initiates a result set retrieval but does not
actually read the result set into the client like mysql_store_result()
does. Instead, each row must be retrieved individually by making calls to
mysql_fetch_row(). This reads the result of a query directly from the
server without storing it in a temporary table or local buffer, which is
somewhat faster and uses much less memory than mysql_store_result().
The client will only allocate memory for the current row and a communication
buffer that may grow up to max_allowed_packet bytes.
On the other hand, you shouldn't use mysql_use_result() if you are
doing a lot of processing for each row on the client side, or if the output
is sent to a screen on which the user may type a ^S (stop scroll).
This will tie up the server and prevent other threads from updating any
tables from which the data is being fetched.
When using mysql_use_result(), you must execute
mysql_fetch_row() until a NULL value is returned, otherwise the
unfetched rows will be returned as part of the result set for your next
query. The C API will give the error Commands out of sync; You can't
run this command now if you forget to do this!
You may not use mysql_data_seek(), mysql_row_seek(),
mysql_row_tell(), mysql_num_rows(), or
mysql_affected_rows() with a result returned from
mysql_use_result(), nor may you issue other queries until the
mysql_use_result() has finished. (However, after you have fetched all
the rows, mysql_num_rows() will accurately return the number of rows
fetched.)
You must call mysql_free_result() once you are done with the result
set.
A MYSQL_RES result structure. NULL if an error occurred.
CR_COMMANDS_OUT_OF_SYNC
CR_OUT_OF_MEMORY
CR_SERVER_GONE_ERROR
CR_SERVER_LOST
CR_UNKNOWN_ERROR
mysql_query() Returns Success, mysql_store_result() Sometimes Returns NULL?
It is possible for mysql_store_result() to return NULL
following a successful call to mysql_query(). When this happens, it
means one of the following conditions occurred:
malloc() failure (for example, if the result set was too
large).
INSERT,
UPDATE, or DELETE).
You can always check whether or not the statement should have produced a
non-empty result by calling mysql_field_count(). If
mysql_field_count() returns zero, the result is empty and the last
query was a statement that does not return values (for example, an
INSERT or a DELETE). If mysql_field_count() returns a
non-zero value, the statement should have produced a non-empty result.
See the description of the mysql_field_count() function for an
example.
You can test for an error by calling mysql_error() or
mysql_errno().
In addition to the result set returned by a query, you can also get the following information:
mysql_affected_rows() returns the number of rows affected by the last
query when doing an INSERT, UPDATE, or DELETE. An
exception is that if DELETE is used without a WHERE clause, the
table is re-created empty, which is much faster! In this case,
mysql_affected_rows() returns zero for the number of records
affected.
mysql_num_rows() returns the number of rows in a result set. With
mysql_store_result(), mysql_num_rows() may be called as soon as
mysql_store_result() returns. With mysql_use_result(),
mysql_num_rows() may be called only after you have fetched all the
rows with mysql_fetch_row().
mysql_insert_id() returns the ID generated by the last
query that inserted a row into a table with an AUTO_INCREMENT index.
See section 22.4.30 mysql_insert_id().
LOAD DATA INFILE ..., INSERT INTO
... SELECT ..., UPDATE) return additional information. The result is
returned by mysql_info(). See the description for mysql_info()
for the format of the string that it returns. mysql_info() returns a
NULL pointer if there is no additional information.
If you insert a record in a table containing a column that has the
AUTO_INCREMENT attribute, you can get the most recently generated
ID by calling the mysql_insert_id() function.
You can also retrieve the ID by using the LAST_INSERT_ID() function in
a query string that you pass to mysql_query().
You can check if an AUTO_INCREMENT index is used by executing
the following code. This also checks if the query was an INSERT with
an AUTO_INCREMENT index:
if (mysql_error(&mysql)[0] == 0 &&
mysql_num_fields(result) == 0 &&
mysql_insert_id(&mysql) != 0)
{
used_id = mysql_insert_id(&mysql);
}
The most recently generated ID is maintained in the server on a
per-connection basis. It will not be changed by another client. It will not
even be changed if you update another AUTO_INCREMENT column with a
non-magic value (that is, a value that is not NULL and not 0).
If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:
INSERT INTO foo (auto,text)
VALUES(NULL,'text'); # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
VALUES(LAST_INSERT_ID(),'text'); # use ID in second table
When linking with the C API, the following errors may occur on some systems:
gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors. No output written to client
If this happens on your system, you must include the math library by
adding -lm to the end of the compile/link line.
The client library is almost thread safe. The biggest problem is
that the subroutines in `net.c' that read from sockets are not
interrupt safe. This was done with the thought that you might want to
have your own alarm that can break a long read to a server. If you
install interrupt handlers for the SIGPIPE interrupt,
the socket handling should be thread safe.
In the older binaries we distribute on our Web site, the client libraries are not normally compiled with the thread-safe option (the windows binaries are by default compiled to be thread safe). Newer binary distributions should have both a normal and a thread-safe client library.
To get a really thread-safe client where you can interrupt the client
from other threads and set timeouts when talking with the MySQL server,
you should use the -lmysys, -lstring, and -ldbug
libraries and the net_serv.o code that the server uses.
If you don't need interrupts or timeouts, you can just compile a tread
safe client library (mysqlclient_r) and use this. See section 22.1 MySQL C API. In this case you don't have to worry about the
net_serv.o object file or the other MySQL libraries.
When using a threaded client and you want to use timeouts and interrupts,
you can make great use of the routines in the `thr_alarm.c' file.
If you are using routines from the mysys library, the only thing
you must remember is to call my_init() first!
All functions except mysql_real_connect() are by default
thread safe. The following notes describe how to compile a thread safe
client library and use it in a thread-safe manner. (The notes below for
mysql_real_connect() actually apply to mysql_connect() as
well, but because mysql_connect() is deprecated, you should be
using mysql_real_connect() anyway.)
To make mysql_real_connect() thread safe, you must recompile the
client library with this command:
shell> ./configure --with-thread-safe-client
This will create a thread-safe client library libmysqlclient_r.
--with-thread-safe-client. This library is thread safe per
connection. You can let two threads share the same connection as long
as you do the following:
mysql_query() and mysql_store_result() no other thread is using
the same connection.
mysql_store_result().
mysql_use_result, you have to ensure that no other thread
is asking anything on the same connection until the result set is closed.
However, it really is best for threaded clients that share the same
connection to use mysql_use_result().
mysql_query() and
mysql_store_result() call combination. Once
mysql_store_result() is ready, the lock can be released and other
threads may query the same connection.
pthread_mutex_lock() and pthread_mutex_unlock() to
establish and release a mutex lock.
You may get some errors because of undefined symbols when linking your
client with mysqlclient_r. In most cases this is because you haven't
included the thread libraries on the link/compile line.
This section documents the Perl DBI interface. The former interface
was called mysqlperl. DBI/DBD now is the
recommended Perl interface, so mysqlperl is obsolete and is not
documented here.
DBI with DBD::mysql
DBI is a generic interface for many databases. That means that
you can write a script that works with many different database engines
without change. You need a DataBase Driver (DBD) defined for each
database type. For MySQL, this driver is called
DBD::mysql.
For more information on the Perl5 DBI, please visit the DBI Web
page and read the documentation:
http://www.symbolstone.org/technology/perl/DBI/index.html
For more information on Object Oriented Programming (OOP) as defined in Perl5, see the Perl OOP page:
http://language.perl.com/info/documentation.html
Installation instructions for MySQL Perl support are given in section 4.11 Perl Installation Comments.
DBI InterfacePortable DBI Methods
connect | Establishes a connection to a database server. |
disconnect | Disconnects from the database server. |
prepare | Prepares a SQL statement for execution. |
execute | Executes prepared statements. |
do | Prepares and executes a SQL statement. |
quote | Quotes string or BLOB values to be inserted.
|
fetchrow_array | Fetches the next row as an array of fields. |
fetchrow_arrayref | Fetches next row as a reference array of fields. |
fetchrow_hashref | Fetches next row as a reference to a hashtable. |
fetchall_arrayref | Fetches all data as an array of arrays. |
finish | Finishes a statement and lets the system free resources. |
rows | Returns the number of rows affected. |
data_sources | Returns an array of databases available on localhost. |
ChopBlanks | Controls whether fetchrow_* methods trim spaces.
|
NUM_OF_PARAMS | The number of placeholders in the prepared statement. |
NULLABLE | Which columns can be NULL.
|
trace | Perform tracing for debugging. |
MySQL-specific Methods
insertid | The latest AUTO_INCREMENT value.
|
is_blob | Which columns are BLOB values.
|
is_key | Which columns are keys. |
is_num | Which columns are numeric. |
is_pri_key | Which columns are primary keys. |
is_not_null | Which columns CANNOT be NULL. See NULLABLE.
|
length | Maximum possible column sizes. |
max_length | Maximum column sizes actually present in result. |
NAME | Column names. |
NUM_OF_FIELDS | Number of fields returned. |
table | Table names in returned set. |
type | All column types. |
The Perl methods are described in more detail in the following sections. Variables used for method return values have these meanings:
$dbh
$sth
$rc
$rv
Portable DBI Methods
connect($data_source, $username, $password)
connect method to make a database connection to the data
source. The $data_source value should begin with
DBI:driver_name:.
Example uses of connect with the DBD::mysql driver:
$dbh = DBI->connect("DBI:mysql:$database", $user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname",
$user, $password);
$dbh = DBI->connect("DBI:mysql:$database:$hostname:$port",
$user, $password);
If the user name and/or password are undefined, DBI uses the
values of the DBI_USER and DBI_PASS environment variables,
respectively. If you don't specify a hostname, it defaults to
'localhost'. If you don't specify a port number, it defaults to the
default MySQL port (3306).
As of Msql-Mysql-modules Version 1.2009,
the $data_source value allows certain modifiers:
mysql_read_default_file=file_name
mysql_read_default_group=group_name
[client] group. By specifying the mysql_read_default_group
option, the default group becomes the [group_name] group.
mysql_compression=1
mysql_socket=/path/to/socket
DBI script, you can take them from the user's `~/.my.cnf'
option file instead by writing your connect call like this:
$dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf",
$user, $password);
This call will read options defined for the [client] group in the
option file. If you wanted to do the same thing but use options specified
for the [perl] group as well, you could use this:
$dbh = DBI->connect("DBI:mysql:$database"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf"
. ";mysql_read_default_group=perl",
$user, $password);
disconnect
disconnect method disconnects the database handle from the database.
This is typically called right before you exit from the program.
Example:
$rc = $dbh->disconnect;
prepare($statement)
($sth), which you can use to invoke
the execute method.
Typically you handle SELECT statements (and SELECT-like statements
such as SHOW, DESCRIBE, and EXPLAIN) by means of
prepare and execute.
Example:
$sth = $dbh->prepare($statement)
or die "Can't prepare $statement: $dbh->errstr\n";
execute
execute method executes a prepared statement. For
non-SELECT statements, execute returns the number of rows
affected. If no rows are affected, execute returns "0E0",
which Perl treats as zero but regards as true. If an error occurs,
execute returns undef. For SELECT statements,
execute only starts the SQL query in the database; you need to use one
of the fetch_* methods described below to retrieve the data.
Example:
$rv = $sth->execute
or die "can't execute the query: $sth->errstr;
do($statement)
do method prepares and executes a SQL statement and returns the
number of rows affected. If no rows are affected, do returns
"0E0", which Perl treats as zero but regards as true. This method is
generally used for non-SELECT statements that cannot be prepared in
advance (due to driver limitations) or that do not need to be executed more
than once (inserts, deletes, etc.). Example:
$rv = $dbh->do($statement)
or die "Can't execute $statement: $dbh- >errstr\n";
Generally the 'do' statement is MUCH faster (and is preferable)
than prepare/execute for statements that don't contain parameters.
quote($string)
quote method is used to "escape" any special characters contained in
the string and to add the required outer quotation marks.
Example:
$sql = $dbh->quote($string)
fetchrow_array
while(@row = $sth->fetchrow_array) {
print qw($row[0]\t$row[1]\t$row[2]\n);
}
fetchrow_arrayref
while($row_ref = $sth->fetchrow_arrayref) {
print qw($row_ref->[0]\t$row_ref->[1]\t$row_ref->[2]\n);
}
fetchrow_hashref
while($hash_ref = $sth->fetchrow_hashref) {
print qw($hash_ref->{firstname}\t$hash_ref->{lastname}\t\
$hash_ref- > title}\n);
}
fetchall_arrayref
my $table = $sth->fetchall_arrayref
or die "$sth->errstr\n";
my($i, $j);
for $i ( 0 .. $#{$table} ) {
for $j ( 0 .. $#{$table->[$i]} ) {
print "$table->[$i][$j]\t";
}
print "\n";
}
finish
$rc = $sth->finish;
rows
SELECT execute
statement. Example:
$rv = $sth->rows;
NULLABLE
NULL values.
Example:
$null_possible = $sth->{NULLABLE};
NUM_OF_FIELDS
SELECT or SHOW FIELDS
statement. You may use this for checking whether a statement returned a
result: A zero value indicates a non-SELECT statement like
INSERT, DELETE, or UPDATE.
Example:
$nr_of_fields = $sth->{NUM_OF_FIELDS};
data_sources($driver_name)
'localhost'.
Example:
@dbs = DBI->data_sources("mysql");
ChopBlanks
fetchrow_* methods will chop
leading and trailing blanks from the returned values.
Example:
$sth->{'ChopBlanks'} =1;
trace($trace_level)
trace($trace_level, $trace_filename)
trace method enables or disables tracing. When invoked as a
DBI class method, it affects tracing for all handles. When invoked as
a database or statement handle method, it affects tracing for the given
handle (and any future children of the handle). Setting $trace_level
to 2 provides detailed trace information. Setting $trace_level to 0
disables tracing. Trace output goes to the standard error output by
default. If $trace_filename is specified, the file is opened in
append mode and output for all traced handles is written to that
file. Example:
DBI->trace(2); # trace everything
DBI->trace(2,"/tmp/dbi.out"); # trace everything to
# /tmp/dbi.out
$dth->trace(2); # trace this database handle
$sth->trace(2); # trace this statement handle
You can also enable DBI tracing by setting the DBI_TRACE
environment variable. Setting it to a numeric value is equivalent to calling
DBI->(value). Setting it to a pathname is equivalent to calling
DBI->(2,value).
MySQL-specific Methods
The methods shown below are MySQL-specific and not part of the
DBI standard. Several of them are now deprecated:
is_blob, is_key, is_num, is_pri_key,
is_not_null, length, max_length, and table.
Where DBI-standard alternatives exist, they are noted below:
insertid
AUTO_INCREMENT feature of MySQL, the new
auto-incremented values will be stored here.
Example:
$new_id = $sth->{insertid};
As an alternative, you can use $dbh->{'mysql_insertid'}.
is_blob
BLOB.
Example:
$keys = $sth->{is_blob};
is_key
$keys = $sth->{is_key};
is_num
$nums = $sth->{is_num};
is_pri_key
$pri_keys = $sth->{is_pri_key};
is_not_null
NULL
values.
Example:
$not_nulls = $sth->{is_not_null};
is_not_null is deprecated; it is preferable to use the
NULLABLE attribute (described above), because that is a DBI standard.
length
max_length
length array indicates the maximum possible sizes that each column may
be (as declared in the table description). The max_length array
indicates the maximum sizes actually present in the result table. Example:
$lengths = $sth->{length};
$max_lengths = $sth->{max_length};
NAME
$names = $sth->{NAME};
table
$tables = $sth->{table};
type
$types = $sth->{type};
DBI/DBD Information
You can use the perldoc command to get more information about
DBI.
perldoc DBI perldoc DBI::FAQ perldoc DBD::mysql
You can also use the pod2man, pod2html, etc., tools to
translate to other formats.
You can find the latest DBI information at
the DBI Web page:
http://www.symbolstone.org/technology/perl/DBI/index.html
The MySQL Contrib directory contains an Eiffel wrapper written by Michael Ravits.
You can also find this at: http://www.netpedia.net/hosting/newplayer/
There are 2 supported JDBC drivers for MySQL (the mm driver and the Reisin JDBC driver). You can find a copy of the mm driver at http://www.mysql.com/Downloads/Contrib/ and the Reisin driver at http://www.caucho.com/projects/jdbc-mysql/index.xtp For documentation consult any JDBC documentation and the driver's own documentation for MySQL-specific features.
PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic Web pages. It contains support for accessing several databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache Web server.
The distribution and documentation are available at the PHP web site.
Two APIs are available in the MySQL Contrib directory.
The MySQL Contrib directory contains a Python interface written by Joseph Skinner.
You can also use the Python interface to iODBC to access a MySQL server. mxODBC
Tcl at binevolve. The Contrib directory contains a Tcl interface that is based on msqltcl 1.50.
mSQLThis section has been written by the MySQL developers, so it should be read with that in mind. But there are NO factual errors that we know of.
For a list of all supported limits, functions, and types, see the
crash-me Web page.
mSQL should be quicker at:
INSERT operations into very simple tables with few columns and keys.
CREATE TABLE and DROP TABLE.
SELECT on something that isn't an index. (A table scan is very
easy.)
mSQL (and
most other SQL implementions) on the following:
SELECT operations.
VARCHAR columns.
SELECT with many expressions.
SELECT on large tables.
mSQL, once one connection
is established, all others must wait until the first has finished, regardless
of whether the connection is running a query that is short or long. When the
first connection terminates, the next can be served, while all the others wait
again, etc.
mSQL can become pathologically slow if you change the order of tables
in a SELECT. In the benchmark suite, a time more than 15000 times
slower than MySQL was seen. This is due to mSQL's lack of a
join optimizer to order tables in the optimal order. However, if you put the
tables in exactly the right order in mSQL2 and the WHERE is
simple and uses index columns, the join will be relatively fast!
See section 12.7 Using Your Own Benchmarks.
ORDER BY and GROUP BY.
DISTINCT.
TEXT or BLOB columns.
GROUP BY and HAVING.
mSQL does not support GROUP BY at all.
MySQL supports a full GROUP BY with both HAVING and
the following functions: COUNT(), AVG(), MIN(),
MAX(), SUM(), and STD(). COUNT(*) is optimized to
return very quickly if the SELECT retrieves from one table, no other
columns are retrieved, and there is no WHERE clause. MIN() and
MAX() may take string arguments.
INSERT and UPDATE with calculations.
MySQL can do calculations in an INSERT or UPDATE.
For example:
mysql> UPDATE SET x=x*10+y WHERE x<20;
SELECT with functions.
MySQL has many functions (too many to list here; see section 7.4 Functions for Use in SELECT and WHERE Clauses).
MEDIUMINT that is 3 bytes long. If you have 100,000,000 records,
saving even one byte per record is very important.
mSQL2 has a more limited set of column types, so it is
more difficult to get small tables.
mSQL stability, so we cannot say
anything about that.
mSQL, and is also less expensive than
mSQL. Whichever product you choose to use, remember to at least
consider paying for a license or e-mail support. (You are required to get
a license if you include MySQL with a product that you sell,
of course.)
mSQL with
some added features.
mSQL has a JDBC driver, but we have too little experience
with it to compare.
GROUP BY, and so on are still not implemented in mSQL, it
has a lot of catching up to do. To get some perspective on this, you
can view the mSQL `HISTORY' file for the last year and
compare it with the News section of the MySQL Reference Manual
(see section E MySQL change history). It should be pretty obvious which one has developed
most rapidly.
mSQL and MySQL have many interesting third-party
tools. Because it is very easy to port upward (from mSQL to
MySQL), almost all the interesting applications that are available for
mSQL are also available for MySQL.
MySQL comes with a simple msql2mysql program that fixes
differences in spelling between mSQL and MySQL for the
most-used C API functions.
For example, it changes instances of msqlConnect() to
mysql_connect(). Converting a client program from mSQL to
MySQL usually takes a couple of minutes.
mSQL Tools for MySQL
According to our experience, it would just take a few hours to convert tools
such as msql-tcl and msqljava that use the
mSQL C API so that they work with the MySQL C API.
The conversion procedure is:
msql2mysql on the source. This requires the
replace program, which is distributed with MySQL.
Differences between the mSQL C API and the MySQL C API are:
MYSQL structure as a connection type (mSQL
uses an int).
mysql_connect() takes a pointer to a MYSQL structure as a
parameter. It is easy to define one globally or to use malloc() to get
one.
mysql_connect() also takes two parameters for specifying the user and
password. You may set these to NULL, NULL for default use.
mysql_error() takes the MYSQL structure as a parameter. Just add
the parameter to your old msql_error() code if you are porting old code.
mSQL returns only a text error message.
mSQL and MySQL Client/Server Communications Protocols DifferThere are enough differences that it is impossible (or at least not easy) to support both.
The most significant ways in which the MySQL protocol differs
from the mSQL protocol are listed below:
mSQL 2.0 SQL Syntax Differs from MySQLColumn types
MySQL
CREATE TABLE Syntax):
ENUM type for one of a set of strings.
SET type for many of a set of strings.
BIGINT type for 64-bit integers.
UNSIGNED option for integer columns.
ZEROFILL option for integer columns.
AUTO_INCREMENT option for integer columns that are a
PRIMARY KEY.
See section 22.4.30 mysql_insert_id().
DEFAULT value for all columns.
mSQL2
mSQL column types correspond to the MySQL types shown below:
mSQL type | Corresponding MySQL type |
CHAR(len) | CHAR(len)
|
TEXT(len) | TEXT(len). len is the maximal length.
And LIKE works.
|
INT | INT. With many more options!
|
REAL | REAL. Or FLOAT. Both 4- and 8-byte versions are available.
|
UINT | INT UNSIGNED
|
DATE | DATE. Uses ANSI SQL format rather than mSQL's own format.
|
TIME | TIME
|
MONEY | DECIMAL(12,2). A fixed-point value with two decimals.
|
Index Creation
MySQL
CREATE TABLE
statement.
mSQL
CREATE INDEX statements.
To Insert a Unique Identifier into a Table
MySQL
AUTO_INCREMENT as a column type
specifier.
See section 22.4.30 mysql_insert_id().
mSQL
SEQUENCE on a table and select the _seq column.
To Obtain a Unique Identifier for a Row
MySQL
PRIMARY KEY or UNIQUE key to the table and use this.
New in Version 3.23.11: If the PRIMARY or UNIQUE key consists of only one
column and this is of type integer, one can also refer to it as
_rowid.
mSQL
_rowid column. Observe that _rowid may change over time
depending on many factors.
To Get the Time a Column Was Last Modified
MySQL
TIMESTAMP column to the table. This column is automatically set
to the current date and time for INSERT or UPDATE statements if
you don't give the column a value or if you give it a NULL value.
mSQL
_timestamp column.
NULL Value Comparisons
MySQL
NULL is always NULL.
mSQL
mSQL, NULL = NULL is TRUE. You
must change =NULL to IS NULL and <>NULL to
IS NOT NULL when porting old code from mSQL to MySQL.
String Comparisons
MySQL
BINARY attribute, which causes comparisons to be done according to the
ASCII order used on the MySQL server host.
mSQL
Case-insensitive Searching
MySQL
LIKE is a case-insensitive or case-sensitive operator, depending on
the columns involved. If possible, MySQL uses indexes if the
LIKE argument doesn't start with a wild-card character.
mSQL
CLIKE.
Handling of Trailing Spaces
MySQL
CHAR and VARCHAR
columns. Use a TEXT column if this behavior is not desired.
mSQL
WHERE Clauses
MySQL
AND is evaluated
before OR). To get mSQL behavior in MySQL, use
parentheses (as shown in an example below).
mSQL
mSQL query:
mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4;To make MySQL evaluate this the way that
mSQL would,
you must add parentheses:
mysql> SELECT * FROM table WHERE (a=1 AND (b=2 OR (a=3 AND (b=4))));
Access Control
MySQL
mSQL
We would first like to note that PostgreSQL and MySQL
are both widely used products, but their design goals are completely
different. This means that for some applications MySQL is more
suitable and for others PostgreSQL is more suitable. When
choosing which database to use, you should first check if the database's
feature set is good enough to satisfy your application. If you need
speed then MySQL is probably your best choice. If you need some
of the extra features that PostgreSQL can offer, you should use
PostgreSQL.
PostgreSQL has some more advanced features like user-defined
types, triggers, rules, and some transaction support (currently it
has about the same symantics as MySQL's transactions in that the
transaction is not 100% atomic). However, PostgreSQL lacks
many of the standard types and functions from ANSI SQL and ODBC. See the
crash-me Web page
for a complete list of limits and which types and functions are supported
or unsupported.
Normally, PostgreSQL is a magnitude slower than
MySQL. See section 12.7 Using Your Own Benchmarks. This is due largely to the fact that they have only
transaction-safe tables and that their transactions system is not as
sophisticated as Berkeley DB's. In MySQL you can decide per
table if you want the table to be fast or take the speed penalty of
making it transaction safe.
The most important things that PostgreSQL supports that MySQL
doesn't yet support:
Sub select
Foreign keys
Stored procedures
An extendable type system.
A way to extend the SQL to handle new key types (like R-trees)
MySQL, on the other hand, supports many ANSI SQL constructs
that PostgreSQL doesn't support. Most of these can be found at the
crash-me Web page.
If you really need the rich type system PostgreSQL offers and you
can afford the speed penalty of having to do everything transaction
safe, you should take a look at PostgreSQL.
This chapter describes a lot of things that you need to know when working on the MySQL code. If you plan to contribute to MySQL development, want to have access to the bleeding-edge in-between versions code, or just want to keep track of development, follow the instructions in See section 4.8 Installing from development source tree. . If you are intersted in MySQL internals you should also subscribe to internals@lists.mysql.com - this is a relatively low traffic list, in comparison with mysql@lists.mysql.com .
The MySQL server creates the following threads:
process_alarm() to force timeouts on connections
that have been idle too long.
-DUSE_ALARM_THREAD, a dedicated thread that
handles alarms is created. This is only used on some systems where
there are some problems with sigwait() or if one wants to use the
thr_alarm() code in ones application without a dedicated signal
handling thread.
--flush_time=# option, a dedicated thread is created
to flush all tables at the given interval.
INSERT DELAYED gets its
own thread.
--master-host, slave replication thread will be
started to read and apply updates from the master.
mysqladmin processlist only shows the connection and INSERT
DELAYED threads.
Since Version 3.23.23, MySQL has support for full-text indexing
and searching. Full-text index in MySQL is an
index of type FULLTEXT. FULLTEXT indexes can be created from
VARCHAR and TEXT columns at CREATE TABLE time or added
later with ALTER TABLE or CREATE INDEX. Full-text search is
performed with the MATCH function:
mysql> CREATE TABLE t (a VARCHAR(200), b TEXT, FULLTEXT (a,b));
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO t VALUES
-> ('MySQL has now support', 'for full-text search'),
-> ('Full-text indexes', 'are called collections'),
-> ('Only MyISAM tables','support collections'),
-> ('Function MATCH ... AGAINST()','is used to do a search'),
-> ('Full-text search in MySQL', 'implements vector space model');
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM t WHERE MATCH (a,b) AGAINST ('MySQL');
+---------------------------+-------------------------------+
| a | b |
+---------------------------+-------------------------------+
| MySQL has now support | for full-text search |
| Full-text search in MySQL | implements vector-space-model |
+---------------------------+-------------------------------+
2 rows in set (0.00 sec)
mysql> SELECT *,MATCH a,b AGAINST ('collections support') as x FROM t;
+------------------------------+-------------------------------+--------+
| a | b | x |
+------------------------------+-------------------------------+--------+
| MySQL has now support | for full-text search | 0.3834 |
| Full-text indexes | are called collections | 0.3834 |
| Only MyISAM tables | support collections | 0.7668 |
| Function MATCH ... AGAINST() | is used to do a search | 0 |
| Full-text search in MySQL | implements vector space model | 0 |
+------------------------------+-------------------------------+--------+
5 rows in set (0.00 sec)
The function MATCH matches a natural language query
AGAINST a text collection (which is simply the columns that are
covered by a FULLTEXT index). For every row in a table it
returns relevance - a similarity measure between the text in that row
(in the columns that are part of the collection) and the query. When it
is used in a WHERE clause (see example above) the rows returned
are automatically sorted with relevance decreasing. Relevance is a
non-negative floating-point number. Zero relevance means no similarity.
Relevance is computed based on the number of words in the row and the
number of unique words in that row, the total number of words in the
collection, the number of documents (rows) that contain a particular
word, etc.
MySQL uses a very simple parser to split text into words. A "word" is
any sequence of letters, numbers, ', and _. Any "word"
that is present in the stopword list or just too short (3 characters
or less) is ignored.
Every correct word in the collection and in the query is weighted, according to its significance in the query or collection. This way, a word that is present in many documents will have lower weight (and may even have a zero weight), because it has lower semantic value in this particular collection. Otherwise, if the word is rare, it will receive a higher weight. Weights of the words are then combined to compute the relevance.
Such a technique works best with big collections (in fact, it was carefully tuned up this way). For very small tables, word distribution does not reflect adequately their semantical value, and this model may sometimes produce bizarre results.
For example, search for the word "search" will produce no results in the above example. Word "search" is present in more than half of rows, and as, such, is effectively treated as stopword (that is, with semantical value zero). It is, really, the desired behavior - natural language query should not return every second row in 1GB table.
The word that select 50% of rows has low ability to locate relevant documents (and will find plenty of unrelevant documents also - we all know this happen too often when we are trying to find something in Internet with search engine), and, as such, has low semantical value in this particular dataset.
Unfortunately, full-text search has no user-tunable parameters yet (but adding some is very high in our TODO). But if one has MySQL source distribution (See section 4.7 Installing a MySQL Source Distribution.) he can somewhat alter full-text search default behaviour.
But note, that full-text search was carefully tuned up for the best search effectivity. Modifying default behaviour will, most probably, make search results only worse. Do not play with MySQL sources, unless you know what you are doing!
myisam/ftdefs.h file by the line
#define MIN_WORD_LEN 4Change it to the value, you prefer, recompile MySQL and rebuild your
FULLTEXT indexes.
myisam/ft_static.c
Modify it to your taste, recompile MySQL and rebuild
your FULLTEXT indexes.
#define GWS_IN_USE GWS_PROBline in
myisam/ftdefs.h to
#define GWS_IN_USE GWS_IDFand recompile MySQL. There is no need to rebuild the indexes though.
Until recently, our main full-coverage test suite was based on
proprietary customer data and for that reason was not publically available. The
only publically available part of our testing process consisted of
crash-me test, the Perl DBI/DBD benchmark found in sql-bench
directory, and miscalaneous tests combined in tests directory. The lack
of a standardazied publically available test suite made it hard for our users
as well as developers to do regression tests on MySQL code. To address this
problem, we have created a new test system that is included in the source
and binary distributions starting in version 3.23.29.
The test system consist of a test language interpreter mysqltest,
mysql-test-run - a shell script to run all tests, the actual test cases
written in a special test language, and their expected results. To run the
test suite on your system after a build, type mysql-test/mysql-test-run
from the source root. If you have installed a binary distribution, cd
to the install root ( eg. /usr/local/mysql ), and do
scripts/mysql-test-run. All tests should succeed. If they do not,
use mysqlbug and send a bug report to bugs@lists.mysql.com.
Make sure to include the output of mysql-test-run, contents of all
.reject files in mysql-test/r directory.
If you have a copy of mysqld running on the machine where you want to
run the test suite you do not have to stop it, as long as it is not using
ports 9306 and 9307. If one of those ports is taken, you should
edit mysql-test-run and change the values of the master and/or slave
port to something not used.
The current set of test cases is far from comprehensive, as we have not yet converted all of our private suite tests to the new format. However, it should already catch most obvious bugs in the SQL processing code, OS/library issues, and is quite thorough in testing replication. Our eventual goal is to have the tests cover 100% of the code. We welcome contributions to our test suite. You may especially want to contribute tests that examine the functionality critical to your system - this will ensure that all MySQL releases will work well with your applications.
You can use mysqltest language to write your own test cases.
Unfortunately, we have not yet written full documentation for it - we plan to
do this shortly. However, you can look at our current test cases and
use them as an example. Also the following points should help you get started:
mysql-test/t/*.test
mysql-test/mysql-test-run test_name
removing .test extension from the file name
; terminated statements and is similar to the
input of mysql command line client. A statement by default is a query
to be sent to MySQL server, unless it is recognized as internal
command ( eg. sleep ).
SELECT, SHOW,
EXPLAIN, etc, must be preceded with @/path/to/result/file. The
file must contain expected results. An easy way to generate the result file
is to run mysqltest -r < t/test-case-name.test from mysql-test
directory, and then edit the generated result files, if needed, to adjust
them to the expected output. In that case, be very careful about not adding or
deleting any invisible characters - make sure to only change the text and/or
delete lines. If you have to insert a line, make sure the fields are separated
with a hard tab, and there is a hard tab at the end. You may want to use
od -c to make sure your text editor has not messed anything up during
edit. We, of course, hope that you will never have to edit the output of
mysqltest -r as you only have to do it when you find a bug.
mysql-test/r directory and name them test_name.result. If the
test produces more than one result, you should use test_name.a.result,
test_name.b.result, etc
.reject extenstion. If your test case is failing, you
should do a diff on the two files. If you cannot see how they are different,
examine both with od -c and also check their lengths.
! if the test can continue after that query
returns an error.
source include/master-slave.inc; at the start of the test file. To
switch between master and slave, use connection master;/
connection slave;. If you need to do something on an alternate
connection, you can do connection master1; for the master, and
connection slave1; on the slave
let $1=1000;
while ($1)
{
# do your queries here
dec $1;
}
sleep command. It supports fractions of
a second, so you can do sleep 1.3;, for example, to sleep 1.3 seconds.
mysql-test/t/test_name-slave.opt. For
the master, put them in mysql-test/t/test_name-master.opt.
Here is a list of all the environment variables that are used directly or indirectly by MySQL. Most of these can also be found in other places in this manual.
Note that any options on the command line will take precedence over values specified in configuration files and environment variables, and values in configuration files take precedence over values in environment variables.
In many cases it's preferable to use a configure file instead of environment variables to modify the behavior of MySQL. See section 4.16.5 Option Files.
CCX | Set this to your C++ compiler when running configure. |
CC | Set this to your C compiler when running configure. |
CFLAGS | Flags for your C compiler when running configure. |
CXXFLAGS | Flags for your C++ compiler when running configure. |
DBI_USER | The default user name for Perl DBI. |
DBI_TRACE | Used when tracing Perl DBI. |
HOME | The default path for the mysql history file is `$HOME/.mysql_history'.
|
LD_RUN_PATH | Used to specify where your libmysqlclient.so is.
|
MYSQL_DEBUG | Debug-trace options when debugging. |
MYSQL_HISTFILE | The path to the mysql history file.
|
MYSQL_HOST | Default host name used by the mysql command-line prompt.
|
MYSQL_PWD | The default password when connecting to mysqld. Note that use of this is insecure! |
MYSQL_TCP_PORT | The default TCP/IP port. |
MYSQL_UNIX_PORT | The default socket; used for connections to localhost.
|
PATH | Used by the shell to finds the MySQL programs. |
TMPDIR | The directory where temporary tables/files are created. |
TZ | This should be set to your local time zone. See section 20.15 Time Zone Problems. |
UMASK_DIR | The user-directory creation mask when creating directories. Note that this is ANDed with UMASK!
|
UMASK | The user-file creation mask when creating files. |
USER | The default user on Windows to use when connecting to mysqld.
|
PHP and MySQLSend any additions to this list to webmaster@mysql.com.
Many users of MySQL have contributed very useful support tools and add-ons.
A list of what is available at http://www.mysql.com/Downloads/Contrib/
(or any mirror) is shown below.
If you want to build MySQL support for the Perl DBI/DBD
interface, you should fetch the Data-Dumper, DBI, and
Msql-Mysql-modules files and install them.
See section 4.11 Perl Installation Comments.
00-README This listing.
Data-Dumper module. Useful with DBI/DBD support for
older Perl installations.
DBI module.
DBD module to access mSQL and MySQL databases.
Data-ShowTable module. Useful with DBI/DBD support.
libmysql.dll, by Blestan Tabakov,
root@tdg.bis.bg.
libmysql.dll, by bsilva@umesd.k12.or.us.
guile that allows guile to interact with SQL
databases. By Hal Roberts.
mydsn.dll. mydsn should be used to build
and remove the DSN registry file for the MyODBC driver in Coldfusion
applications. By Miguel Angel Solórzano.
user, db and
host tables. By Tim Sailer, modified by Atif Ghaffar
aghaffar@artemedia.ch.
DBI:DBD and CGI.pm.
FutureSQL allows one to easily set up config files to view, edit, delete,
and otherwise process records from a MySQL database. It uses a data
dictionary, configuration files and templates, and allows "pre-processing"
and "post-processing" on both fields, records, and operations.
DBI 1.06.
BLOB/TEXT columns by Daniel Koch.
mod_auth_mysql. This is a little tool that allows you
to add/change user records storing group and/or password entries in
MySQL tables. By Harry Brueckner, brueckner@respublica.de.
mod_auth_mysql. This is a two-part system for use with
mod_auth_mysql.
pam, using MySQL.
mysqldump output to a C header file. By Harry Brueckner,
brueckner@mail.respublica.de.
access_to_mysql.txt, except that this
one is fully configurable, has better type conversion (including
detection of TIMESTAMP fields), provides warnings and suggestions
while converting, quotes all special characters in text and
binary data, and so on. It will also convert to mSQL v1 and v2,
and is free of charge for anyone. See
http://www.cynergi.net/prod/exportsql/ for the latest version. By
Pedro Freire, support@cynergi.net. NOTE: Doesn't work with
Access2!
exportsql. By Brian Andrews.
NOTE: Doesn't work with Access2!
exportsql.txt. That is,
it imports data from MySQL into an Access database via
ODBC. This is very handy when combined with exportsql, because it lets you
use Access for all DB design and administration, and synchronize with
your actual MySQL server either way. Free of charge. See
http://www.netdive.com/freebies/importsql/ for any updates.
Created by Laurent Bossavit of NetDIVE.
NOTE: Doesn't work with Access2!
mSQL to MySQL. By alfred@sb.net
mysqldump and pipe it to
the sqlconv.pl script. The script will parse through the
mysqldump output and will rearrange the fields so they can be
inserted into a new table. An example is when you want to create a new
table for a different site you are working on, but the table is just a
bit different (that is - fields in different order, etc.).
By Steve Shreeve.
radiusd to make it support MySQL. By Wim Bonis,
bonis@kiss.de.
hylafax outgoing faxes in a MySQL database. By Sinisa
Milivojevic, sinisa@mysql.com.
The following persons have helped us make MySQL what it is today
Developers that are or have been employed by MySQL AB to work on MySQL. (Roughly in the order they started to work with us.)
mysqld.
mysys library.
ISAM and MyISAM libraries (B-tree index file
handlers with index compression and different record formats).
HEAP library. A memory table system with our superior full dynamic
hashing. In use since 1981 and published around 1984.
replace program (look into it, it's COOL!).
mSQL tools like msqlperl, DBD/DBI, and
DB2mysql.
texi2html.
libtool support.
mysys are left.
mysqlimport
mysql client.
procedure analyse()
zlib) in the client/server protocol.
RAID support for MyISAM tables.
SHOW TABLE CREATE.
MERGE library.
ALTER TABLE ... ORDER BY ....
The following non-developers are also working in/with MySQL AB:
Contributors to the MySQL distribution are listed below, in somewhat random order:
mysqlshutdown.exe and
mysqlwatch.exe
mSQL, but found that it couldn't satisfy our purposes so instead we
wrote a SQL interface to our application builder Unireg. mysqladmin
and mysql are programs that were largely influenced by their
mSQL counterparts. We have put a lot of effort into making the
MySQL syntax a superset of mSQL. Many of the API's ideas are
borrowed from mSQL to make it easy to port free mSQL programs
to MySQL. MySQL doesn't contain any code from mSQL.
Two files in the distribution (`client/insert_test.c' and
`client/select_test.c') are based on the corresponding (non-copyrighted)
files in the mSQL distribution, but are modified as examples showing
the changes necessary to convert code from mSQL to MySQL.
(mSQL is copyrighted David J. Hughes.)
WHERE column REGEXP regexp.
gcc), the libc library
(from which we have borrowed `strto.c' to get some code working in Linux),
and the readline library (for the mysql client).
http://www.mysql.com/.
mysqldump (previously msqldump, but ported and enhanced by
Monty).
DBD (Perl) interface.
mysqlhotcopy.
_MB character set macros and the ujis and sjis character sets.
mysqlaccess, a program to show the access rights for a user.
xmysql, a graphical X client for MySQL.
DBD::mysql module.
FROM_UNIXTIME() time formatting, ENCRYPT() functions, and
bison advisor.
Active mailing list member.
DBI/DBD. Have
been of great help with crash-me and running benchmarks. Some new
date functions. The mysql_setpermissions script.
DBI/DBD section in the manual.
CREATE FUNCTION and
DROP FUNCTION.
AGGREGATE extension to UDF functions.
mysqlaccess more secure.
Other contributors, bugfinders, and testers: James H. Thompson, Maurizio Menghini, Wojciech Tryc, Luca Berra, Zarko Mocnik, Wim Bonis, Elmar Haneke, jehamby@lightside, psmith@BayNetworks.com, duane@connect.com.au, Ted Deppner ted@psyber.com, Mike Simons, Jaakko Hyvatti.
And lots of bug report/patches from the folks on the mailing list.
And a big tribute to those that help us answer questions on the
mysql@lists.mysql.com mailing list:
DBD-mysql questions.
xmysql-related questions and basic installation questions.
mysqlbug.
DBD, Linux, some SQL syntax questions.
Note that we tend to update the manual at the same time we implement new things to MySQL. If you find a version listed below that you can't find on the MySQL download page, this means that the version has not yet been released!
The 3.23 release has several major new features that are not present in the 3.22 or 3.21 releases. We have added two new table types: MyISAM, a new ISAM library which is tuned for SQL and supports large files; and BerkeleyDB which uses the Berkeley DB library from Sleepycat Software to implement transaction-safe tables. The 3.23 release also includes support for database replication between a master and many slaves.
We are not adding any more new features that are likely to break any old code in MySQL Version 3.23, so we recommend that you use this version. The replication and BerkeleyDB code is still under development, though, so Version 3.23 is not released as a stable version yet.
REPLACE with BDB tables.
LPAD() and RPAD() will shorten the result string if it's longer
than the length argument.
SHOW LOGS command.
PRIMARY keys first, followed by
UNIQUE keys.
UPDATE involving multi-part keys where one
specified all key parts both in the update and the WHERE part. In
this case MySQL could try to update a record that didn't match
the whole WHERE part.
.frm file.
mysqld to report the
hostname as '' in some error messages.
HEAP type tables; the variable
max_heap_table_size wasn't used. Now either MAX_ROWS or
max_heap_table_size can be used to limit the size of a HEAP
type table.
bdb_lock_max to bdb_max_lock.
auto_increment on sub fields for BDB tables.
ANALYZE of BDB tables.
ROLLBACK when you have updated a non-transactional table
you will get an error as a warning.
--bdb-shared-data to mysqld.
Slave_open_temp_tables.
binlog_cache_size and max_binlog_cache_size to
mysqld.
DROP TABLE, RENAME TABLE, CREATE INDEX and
DROP INDEX are now transaction endpoints.
DROP DATABASE on a symbolic linked database, both
the link and the original database is deleted.
DROP DATABASE works on OS/2.
SELECT DISTINCT ... table1 LEFT JOIN
table2.. when table2 was empty.
--abort-slave-event-count and
--disconnect-slave-event-count options to mysqld for
debugging and testing of replication.
SHOW KEYS now shows whether or not key is FULLTEXT.
mysqld_multi. See section 14.3 mysqld_multi, program for managing multiple MySQL servers.
mysqld processes.
mysqld handles them by default.
FULLTEXT indexes in one table.
REPAIR/OPTIMIZE.
Yuri Dario.
FLUSH TABLES table_name didn't always flush the index tree
properly to disk.
--bootstrap is now run in a separate thread. This fixes the problem
that mysql_install_db core dumped on some Linux machines.
mi_create() to use less stack.
MATCH when used
with UNIQUE key.
crash-me and the MySQL benchmarks to also work
with FrontBase.
RESTRICT and CASCADE after DROP TABLE to make
porting easier.
--slow-log.
connect_timeout to mysql and mysqladmin.
connect_timeout as an alias for timeout for option files
read by mysql_options().
--pager[=...], --no-pager,
--tee=... and --no-tee to the mysql client. The
new corresponding interactive commands are pager, nopager,
tee and notee. See section 14.4 The Command-line Tool, mysql --help and the
interactive help for more information.
MyISAM table failed.
SELECT, UPDATE and INSERT
statements running. The symptom was that the UPDATE and
INSERT queries was locked a long time while new SELECT
statements where executed before the updates.
mysql_options() the
return-found-rows option was ignored.
interactive-timeout in the option file that
is read by mysql_options(). This makes it possible to force
programs that run for a long time (like mysqlhotcopy) to use
interactive_timeout instead of wait_timeout.
--log-long-format then also queries that
are not using indexes are logged, even the query takes less than
long_query_time seconds.
LEFT JOIN which caused all columns in a reference
table to be NULL.
NATURAL JOIN without keys.
TEXT or BLOB.
DROP of temporary tables wasn't stored in the update/binary log.
SELECT DISTINCT * ... LIMIT # only returned one row.
strstr() for sparc and cleaned up
the `global.h' header file to avoid a problem with bad aliasing with
the compiler submitted with RedHat 7.0. (Reported by Trond Eivind Glomsrød)
--skip-networking now works properly on NT.
ISAM tables when a row with a length
of more than 65K was shortened by a single byte.
MyISAM when running multiple updating processes on
the same table.
FLUSH TABLE tablename.
--replicate-ignore-table, --replicate-do-table,
--replicate-wild-ignore-table, --replicate-wild-do-table
IO_CACHE mechanism instead of
FILE to avoid OS problems when there are many files open.
--open-files and --timezone to safe_mysqld.
CREATE TEMPORARY TABLE ... SELECT ....
CREATE TABLE ... SELECT NULL.
large_file_support,net_read_timeout,
net_write_timeout and query_buffer_size to SHOW VARIABLES.
created_tmp_files and sort_merge_passes
to SHOW STATUS.
FOREIGN KEY definition.
TRUNCATE table_name as a synonym for
DELETE FROM table_name.
bdb_lock_max to mysqld.
mysql_connect() now aborts on Linux if the server doesn't answer in
timeout seconds.
SLAVE START did not work if you started with
--skip-slave-start and had not explicitly run CHANGE
MASTER TO.
SHOW MASTER STATUS to be consistent with
SHOW SLAVE STATUS. (It now has no directory in the log name.)
PURGE MASTER LOGS TO.
SHOW MASTER LOGS.
--safemalloc-mem-limit option to mysqld to simulate memory
shortage when compiled --with-debug=full.
SHOW SLAVE STATUS was using an unititialized mutex if the slave had
not been started yet.
ELT() and MAKE_SET() when the query used
a temporary table.
CHANGE MASTER TO without specifying MASTER_LOG_POS would
set it to 0 instead of 4 and hit the magic number in the master binlog.
ALTER TABLE ... ORDER BY ... syntax added. This will create the
new table with the rows in a specific order.
SHOW CREATE when using AUTO_INCREMENT columns.
mit-pthreads.
<> to work properly with NULL.
SUBSTRING_INDEX() and REPLACE().
(Patch by Alexander Igonitchev)
CREATE TEMPORARY TABLE IF NOT EXISTS not to give an error
if the table exists.
PRIMARY KEY in a BDB table, a hidden
PRIMARY KEY will be created.
LEFT JOIN in some cases preferred a full table scan when there was
no WHERE clause.
--log-slow-queries, don't count the time waiting for a lock.
MyISAM tables if you start mysqld with
--myisam-recover.
TYPE= keyword from CHECK and
REPAIR. Allow CHECK options to be combined. (You can still
use TYPE= but this usage is deprecated.)
--replicate-rewrite-db option to mysqld.
--skip-slave-start option to mysqld.
INSERT INTO foo(some_key)
values (1),(1)) erroneously terminated the slave thread.
DISTINCT is only used on columns
from some of the tables.
SHOW GRANTS didn't always show all column grants.
--default-extra-file=# to all MySQL clients.
INSERT statements now are initialized properly.
UPDATE didn't always work when used with a range on a timestamp that
was part of the key that was used to find rows.
FULLTEXT index when inserting a NULL column.
mkstemp() instead of tempnam(). Based
on a patch from John Jones.
mysqlhotcopy.
UMASK and UMASK_DIR can now be specified in octal.
RIGHT JOIN. This makes RIGHT a reserved word.
@@IDENTITY as a synonym for LAST_INSERT_ID().
(This is for Visual Basic compatibility.)
myisamchk and REPAIR when using FULLTEXT
index.
LOAD DATA INFILE now works with FIFOs.
(Patch by Toni L. Harbaugh-Blackford.)
FLUSH LOGS broke replication if you specified a log name with an
explicit extension as the value of the log-bin option.
MyISAM with packed multi-part keys.
CHECK TABLE on Windows.
FULLTEXT index always used the koi8_ukr
character set.
CHECK TABLE.
MyISAM repair/reindex code didn't use the --tempdir
option for its temporary files.
BACKUP TABLE/RESTORE TABLE.
CHANGE MASTER TO when the slave did not have
the master to start with.
Time in the processlist for Connect of
the slave thread.
FLUSH MASTER if you didn't specify
a filename argument to --log-bin.
--memlock option to mysqld to lock mysqld
in memory on systems with the mlockall() call (like in Solaris).
HEAP tables didn't use keys properly. (Bug from 3.23.23.)
MERGE tables (keys, mapping, creation,
documentation...). See section 8.2 MERGE Tables.
mysqldump from 3.23 which caused some CHAR columns
not to be quoted.
analyze, check, optimize and repair code.
OPTIMIZE TABLE is now mapped to REPAIR with statistics and
sorting of the index tree. This means that for the moment it only
works on MyISAM tables.
ORDER BY bug with BDB tables.
mysqld couldn't remove the `.pid' file
under Windows.
--log-isam to log MyISAM tables instead of isam
tables.
CHECK TABLE to work on Windows.
pwrite() safe on Windows.
mysqld variable created_tmp_disk_tables.
TIMESTAMP(X) columns, MySQL now reports columns with X
other than 14 or 8 to be strings.
CHAR columns that may have characters with ASCII
values greater than 128 that was created or modified with 3.23.22 must
be repaired!
REPAIR TABLE or myisamchk before use!
--core-file to mysqld to get a core file on
Linux if mysqld dies on the SIGSEGV signal.
mysql now starts with option
--no-named-commands (-g) by default. This option can be
disabled with --enable-named-commands (-G). This may cause
incompatibility problems in some cases, for example, in SQL scripts that
use named commands without a semicolon, etc. ! Long format commands
still work from the first line.
DROP TABLE statements at
the same time.
LEFT JOIN on an
empty table.
mysqld with incorrect options.
free() bug in mysqlimport.
MyISAM index handling of
DECIMAL/NUMERIC keys.
MyISAM tables; In some contexts,
usage of MIN(key_part) or MAX(key_part) returned an empty set.
mysqlhotcopy to use the new FLUSH TABLES table_list
syntax. Only tables which are being backed up are flushed now.
--enable-thread-safe-client so
that both non-threaded (-lmysqlclient) and threaded
(-lmysqlclient_r) libraries are built. Users who linked
against a threaded -lmysqlclient will need to link against
libmysqlclient_r now.
RENAME command.
NULL in COUNT(DISTINCT ...).
ALTER TABLE, LOAD DATA INFILE on empty tables and
INSERT ... SELECT ... on empty tables to create non-unique indexes
in a separate batch with sorting. This will make the above calls much
faster when you have many indexes.
ALTER TABLE now logs the first used insert_id correctly.
BLOB column.
DATE_ADD/DATE_SUB where it returned a datetime instead
of a date.
***DEAD*** in SHOW PROCESSLIST.
pthread_rwlock_rdlock code.
SELECT on part keys works with BDB tables.
INSERT INTO bdb_table ... SELECT to work with BDB tables.
CHECK TABLE now updates key statistics for the table.
ANALYZE TABLE will now only update tables that have been changed
since thee last ANALYZE. Note that this is a new feature and tables
will not be marked to be analyzed until they are updated in any way with
3.23.23 or newer. For older tables, you have to do CHECK TABLE
to update the key distribution.
CHECK, ANALYZE,
REPAIR and SHOW CREATE commands.
CHANGE MASTER TO command.
FAST, QUICK EXTENDED check types to
CHECK TABLES.
myisamchk so that --fast and
--check-changed-tables are also honored with --sort-index and
--analyze.
LOAD TABLE FROM MASTER that did not lock the
table during index re-build.
LOAD DATA INFILE broke replication if the database was excluded
from replication.
SHOW SLAVE STATUS and SHOW MASTER STATUS.
SLAVE STOP now will not return until the slave thread actually exits.
MATCH function and FULLTEXT index type.
(For MyISAM files). This makes FULLTEXT a reserved word.
lex_hash.h is created properly for each MySQL
distribution.
MASTER and COLLECTION are not reserved words.
--slow-query-log didn't contain the whole queries.
gcc 2.96 (intel) and gcc 2.9
(Ia64) in gen_lex_hash.c.
host= in the
my.cnf file.
DATE_ADD()/DATE_SUB()
against a number.
-F, --fast for myisamchk. Added option
-C, --check-only-changed to myisamchk.
ANALYZE table_name to update key statistics for tables.
0x... to be regarded as integers by default.
SHOW PROCESSLIST.
auto-rehash on reconnect for the mysql client.
MyISAM, where the index file couldn't
get bigger than 64M.
SHOW MASTER STATUS and SHOW SLAVE STATUS.
mysql_character_set_name(MYSQL *mysql) function to the
MySQL C API.
ASCII 0 safe.
mysql_config script.
< or > with a char column that was only
partly indexed.
mysqladmin to use the CREATE DATABASE/DROP
DATABASE commands instead of the old deprecated API calls.
chown warning in safe_mysqld.
ORDER BY that was introduced in 3.23.19.
DELETE FROM tbl_name to do a drop+create of
the table if we are in AUTOCOMMIT mode. (Needed for BDB tables).
ISAM/MyISAM
index files gets full during an INSERT/UPDATE.
myisamchk didn't correctly update row checksum when used with
-ro (This only gave an warning in subsequent runs).
REPAIR TABLE so that it works with tables without indexes.
DROP DATABASE
LOAD TABLE FROM MASTER is sufficiently bug-free to announce it as
a feature.
MATCH and AGAINST are now reserved words.
DELETE FROM tbl_name removed the .frm file.
MyISAM table
when doing update based on key on a table with many keys and some key changed
values.
ORDER BY can now uses REF keys to find subset the rows
that needs to be sorted.
print_defaults to my_print_defaults to avoid
name confusion.
NULLIF() to work according to ANSI SQL99.
net_read_timeout and net_write_timeout as startup
parameters to mysqld.
myisamchk --sort-records
on a table with prefix compressed index.
BEGIN WORK (the same as BEGIN).
ORDER BY on a CONV() expression.
LOAD TABLE FROM MASTER
FLUSH MASTER and FLUSH SLAVE
FLUSH TABLES WITH READ LOCK to make a global lock suitable to
make a copy of MySQL data files.
CREATE TABLE ... SELECT ... PROCEDURE now works.
GROUP BY on VARCHAR/CHAR columns.
READ and a
WRITE lock.
RAID tables.
find_in_set() when the first argument was NULL.
LEFT JOIN and ORDER BY where the first
table had only one matching row.
my.cfg example files in the `support-files'
directory.
duplicated key problem when doing big GROUP BY's.
(This bug was probably introduced in 3.23.15).
INNER JOIN to match ANSI SQL.
NATURAL JOIN syntax.
BDB interface.
--no-defaults and --defaults-file to
safe_mysqld.sh and mysql_install_db.sh.
USE INDEX works with PRIMARY keys.
BEGIN statement to start a transaction in AUTOCOMMIT mode.
KILL now works on a thread that is locked on a 'write' to a dead client.
log-slave-updates to allow daisy-chaining the slaves.
pthread_t
is not the same as int.
INSERT DELAYED code when doing
ALTER TABLE.
INSERT DELAYED
TYPE=QUICK to CHECK and REPAIR.
REPAIR TABLE when the table was in use by other threads.
gdb when one does a lot of reconnects. This will also improve
systems where you can't use persistent connections.
UPDATE IGNORE will not abort if an update results in a
DUPLICATE_KEY error.
CREATE TEMPORARY TABLE commands in the update log.
delayed_key_writes tables and CHECK TABLE.
replicate-do-db and replicate-ignore-db options to
restrict which databases get replicated
SQL_LOG_BIN option
mysqld as root, you must now use the --user=root option.
FLUSH TABLES command.
slow_launch_time variable and the Slow_launch_threads
status variable to mysqld. These can be examined with
mysqladmin variables and mysqladmin extended-status.
INET_NTOA() and INET_ATON().
IF() now depends on the second and
third arguments and not only on the second argument.
myisamchk could go into a loop when trying to
repair a crashed table.
INSERT DELAYED to update log if SQL_LOG_UPDATE=0.
REPLACE on HEAP tables.
SHOW VARIABLES.
DELETE of many rows on a table with
compressed keys where MySQL scanned the index to find the rows.
CHECK on table with deleted keyblocks.
LAST_INSERT_ID() to update
a table with an auto_increment key.
NULLIF().
LOAD DATA INFILE on a table with
BLOB/TEXT columns.
EXPLAIN SELECT ... now also prints out whether MySQL needs to
create a temporary table or use file sorting when resolving the SELECT.
ORDER BY parts where the part is a
constant expression in the WHERE part. Indexes can now be used
even if the ORDER BY doesn't match the index exactly, as long as
all the not used index parts and all the extra ORDER BY
columns are constants in the WHERE clause. See section 12.4 How MySQL Uses Indexes.
UPDATE and DELETE on a whole unique key in the WHERE part,
is now faster than before.
RAID_CHUNKSIZE to be in 1024 byte increments.
CONCAT() where one of the arguments was a function
that returned a modified argument.
myisamchk, where it updated the header in
the index file when one only checked the table. This confused the
mysqld daemon if it updated the same table at the same time. Now
the status in the index file is only updated if one uses
--update-state. With older myisamchk versions you should
use --read-only when only checking tables, if there is the
slightest chance that the mysqld server is working on the table at the
same time!
DROP TABLE is logged in the update log.
DECIMAL() key field
where the column data contained leading zeros.
myisamchk when the auto_increment isn't the first key.
DATETIME in ISO8601 format: 2000-03-12T12:00:00
mysqld binary can now handle many different
character sets (you can choose which when starting mysqld).
REPAIR TABLE.
mysql_thread_safe().
UMASK_DIR environment variable.
CONNECTION_ID().
= on BLOB or VARCHAR BINARY keys, where
only a part of the column was indexed, the whole column of the result
row wasn't compared.
ORDER BY.
GROUP BY part.
LOCK TABLE command; This fixed the problem one got when running
the test-ATIS test with --fast or --check-only-changed.
SQL_BUFFER_RESULT to SELECT.
CHECK TABLE command.
MyISAM involving REPLACE ... SELECT ... which could
give a corrupted table.
myisamchk where it wrongly reset the auto_increment value.
DISTINCT on HEAP temporary tables to use hashed
keys to quickly find duplicated rows. This mostly concerns queries of
type SELECT DISTINCT ... GROUP BY .... This fixes a problem where
not all duplicates were removed in queries of the above type. In
addition, the new code is MUCH faster.
IF NOT EXISTS to CREATE DATABASE.
--all-databases and --databases to mysqldump
to allow dumping of many databases at the same time.
DECIMAL() index in MyISAM tables.
mysqladmin shutdown on a local connection, mysqladmin now
waits until the pidfile is gone before terminating.
COUNT(DISTINCT ...) queries.
myisamchk works properly with RAID:ed tables.
LEFT JOIN and key_field IS NULL.
net_clear() which could give the error Aborted
connection in the MySQL clients.
USE INDEX (key_list) and IGNORE INDEX (key_list) as
join parameters in SELECT.
DELETE and RENAME should now work on RAID tables.
ALTER TABLE tbl_name ADD (field_list) syntax.
GRANT/REVOKE ALL PRIVILEGES doesn't affect
GRANT OPTION.
) from the output of SHOW GRANTS
UNIQUE INDEX in CREATE statements.
mysqlhotcopy - fast on-line hot-backup utility for local
MySQL databases. By Tim Bunce.
mysqlaccess. Thanks to Steve Harvey for this.
--i-am-a-dummy and --safe-updates to mysql.
select_limit and max_join_size to mysql.
SQL_MAX_JOIN_SIZE and SQL_SAFE_UPDATES.
READ LOCAL lock that doesn't lock the table for concurrent
inserts. (This is used by mysqldump).
LOCK TABLES ... READ doesn't anymore allow concurrent
inserts.
--skip-delay-key-write to mysqld.
_rowid can now be used as an alias for an integer type unique indexed
column.
SIGPIPE when compiling with --thread-safe-clients
to make things safe for old clients.
LOCK TABLES.
INSERT DELAYED.
date_column BETWEEN const_date AND const_date works.
NULL in a table with
BLOB/TEXT columns.
WHERE K1=1 and K3=2 and (K2=2 and K4=4 or K2=3 and K4=5)
source to mysql to allow reading of batch files
inside the mysql client. Original patch by Matthew Vanecek.
WITH GRANT OPTION option.
GRANT error when using tables from many
databases in the same query.
SELECT when using many overlapping indexes.
MySQL should now be able to choose keys even better when there
is many keys to choose from.
SELECT * from key_part_1=const and key_part_2 > const2
VARCHAR columns to CHAR columns
didn't change row type from dynamic to fixed.
SELECT floor(pow(2,63)).
mysqld startup option --delay-key-write to
--delay-key-write-for-all-tables
read-next-on-key to HEAP tables. This should fix all
problems with HEAP tables when using not UNIQUE keys.
--log-slow-queries to mysqld to log all queries that take a
long time to a separate log file with a time of how long the query took.
WHERE key_column=RAND(...)
SELECT ... LEFT JOIN ... key_column IS NULL,
when key_column could contain NULL values.
LOAD DATA INFILE.
NISAM.
ISAM when doing some ORDER BY ... DESC queries.
--delay-key-write didn't enable delayed key writing.
TEXT column which only involved case changes.
INSERT DELAYED doesn't update timestamps that are given.
YEARWEEK() and options x, X, v and
V to DATE_FORMAT().
MAX(indexed_column) and HEAP tables.
BLOB NULL keys and LIKE "prefix%".
MyISAM and fixed-length rows < 5 bytes.
GROUP BY queries.
ENUM field value
was too big.
pthread_mutex_timedwait,
which is used with INSERT DELAYED. See section 4.12.5 Linux Notes (All Linux Versions).
MyISAM with keys > 250 characters.
MyISAM one can now do an INSERT at the same time as other
threads are reading from the table.
max_write_lock_count to mysqld to force a
READ lock after a certain number of WRITE locks.
delayed_key_write on show variables.
concurrency to thread_concurrency.
LOCATE(substr,str), POSITION(substr IN str),
LOCATE(substr,str,pos), INSTR(str,substr),
LEFT(str,len), RIGHT(str,len),
SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len),
MID(str,pos,len), SUBSTRING(str,pos), SUBSTRING(str
FROM pos), SUBSTRING_INDEX(str,delim,count), RTRIM(str),
TRIM([[BOTH | TRAILING] [remstr] FROM] str),
REPLACE(str,from_str,to_str), REVERSE(str),
INSERT(str,pos,len,newstr), LCASE(str), LOWER(str),
UCASE(str) and UPPER(str); Patch by Wei He.
FULL to SHOW PROCESSLIST.
--verbose to mysqladmin.
REPLACE() and LOAD DATA INFILE.
mysqld variable interactive_timeout.
mysql_data_seek() from ulong to
ulonglong.
mysqld option -O lower_case_table_names={0|1} to allow
users to force table names to lowercase.
SELECT ... INTO DUMPFILE.
--ansi to make some functions ANSI SQL
compatible.
#sql.
` (" in --ansi mode).
[floor() overflow safe on FreeBSD.
--quote-names to mysqldump
PRIMARY KEY NOT NULL.
encrypt() to be thread safe and not reuse buffer.
mysql_odbc_escape_string() function to support big5 characters in
MyOBC.
FLOAT and DOUBLE (without any length modifiers) are
not anymore fixed decimal point numbers.
FLOAT(X): Now this is the same as FLOAT if
X <= 24 and a DOUBLE if 24 < X <= 53.
DECIMAL(X) is now an alias for DECIMAL(X,0) and DECIMAL
is now an alias for DECIMAL(10,0). The same goes for NUMERIC.
ROW_FORMAT={default | dynamic | static | compressed} to
CREATE_TABLE.
DELETE FROM table_name didn't work on temporary tables.
CHAR_LENGTH() to be multi-byte character safe.
ORD(string).
SELECT DISTINCT ... ORDER BY RAND().
ALTER TABLE + adding a column after the last field didn't work.
CREATE TABLE foo (a int not null auto_increment, b char(5), primary key (b,a))
NULL.
AS on fieldname with CREATE TABLE table_name SELECT ... didn't
work.
NATIONAL and NCHAR when defining character columns.
This is the same as not using BINARY.
NULL columns in a PRIMARY KEY (only in UNIQUE
keys).
LAST_INSERT_ID if one uses this in ODBC:
WHERE auto_increment_column IS NULL. This seems to fix some problems
with Access.
SET SQL_AUTO_IS_NULL=0|1 now turns on/off the handling of
searching after the last inserted row with WHERE
auto_increment_column IS NULL.
mysqld variable concurrency for Solaris.
--relative to mysqladmin to make
extended-status more useful to monitor changes.
COUNT(DISTINCT ...) on an empty table.
LOAD DATA INFILE and BLOB columns.
~ (negation).
UDF functions.
DATETIME into a TIME column will not anymore
try to store 'days' in it.
SUM().)
LIKE "%" on an index that may have NULL values.
REVOKE ALL PRIVILEGES didn't revoke all privileges.
SHOW GRANTS FOR user (by Sinisa).
date_add syntax: date/datetime + INTERVAL # interval_type.
By Joshua Chamas.
LOAD DATA REPLACE.
REGEXP is now case insensitive if you use non-binary strings.
ASC is now the default again for ORDER BY.
LIMIT to UPDATE.
mysql_change_user().
SHOW VARIABLES.
--[whitespace] comments.
INSERT into tbl_name VALUES (), that is, you may now specify
an empty value list to insert a row in which each column is set to its
default value.
SUBSTRING(text FROM pos) to conform to ANSI SQL. (Before this
construct returned the rightmost 'pos' characters).
SUM() with GROUP BY returned 0 on some systems.
SHOW TABLE STATUS.
DELAY_KEY_WRITE option to CREATE TABLE.
AUTO_INCREMENT on any key part.
YEAR(NOW()) and YEAR(CURDATE()).
CASE construct.
COALESCE().
SELECT * FROM table_name WHERE
key_part1 >= const AND (key_part2 = const OR key_part2 = const). The
bug was that some rows could be duplicated in the result.
myisamchk without -a updated the index
distribution wrong.
SET SQL_LOW_PRIORITY_UPDATES=1 gave parse error before.
WHERE clause.
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100
SELECT ... WHERE key_part1=const1 AND
key_part_2=const2 AND key_part1=const4 AND key_part2=const4 ; Indextype
should be range instead of ref.
egcs 1.1.2 optimizer bug (when using BLOBs) on Linux Alpha.
LOCK TABLES combined with DELETE FROM table.
NULL and BLOB/TEXT columns.
SELECT ... FROM t1 LEFT JOIN t2 ON ... WHERE t2.not_null_column IS NULL.
ORDER BY and GROUP BY can be done on functions.
ORDER BY RAND().
WHERE key_column = function.
WHERE key_column = column_name even if
the columns are not identically packed.
WHERE column_name IS NULL.
--init-file=file_name to mysqld.
COUNT(DISTINCT value, [value, ...])
CREATE TEMPORARY TABLE now creates a temporary table, in its own
namespace, that is automatically deleted if connection is dropped.
CASE): CASE, THEN, WHEN, ELSE and END.
EXPORT_SET() and MD5().
MyISAM) with a lot of new features.
See section 8.1 MyISAM Tables.
HEAP tables which are extremely fast for
lookups.
LOAD_FILE(filename) to get the contents of a file as a
string value.
<=> which will act as = but will return TRUE
if both arguments are NULL. This is useful for comparing changes
between tables.
EXTRACT(interval FROM datetime) function.
FLOAT(X) is not rounded on storage and may be
in scientific notation (1.0 E+10) when retrieved.
REPLACE is now faster than before.
LIKE character comparison to behave as =;
This means that 'e' LIKE ''e' (if the line doesn't display
correctly, the latter 'e' means a French 'e' with a dot above) is now true.
SHOW TABLE STATUS returns a lot of information about the tables.
LIKE to the SHOW STATUS command.
SHOW COLUMNS.
packed and comment to SHOW INDEX.
CREATE TABLE ... COMMENT "xxx").
UNIQUE, as in
CREATE TABLE table_name (col int not null UNIQUE)
CREATE TABLE table_name SELECT ...
CREATE TABLE IF NOT EXISTS ...
CHAR(0) columns.
DATE_FORMAT() now requires `%' before any format character.
DELAYED is now a reserved word (sorry about that :( ).
analyse, file: `sql_analyse.c'.
This will describe the data in your query. Try the following:
SELECT ... FROM ... WHERE ... PROCEDURE ANALYSE([max elements,[max memory]])This procedure is extremely useful when you want to check the data in your table!
BINARY cast to force a string to be compared case sensitively.
--skip-show-database to mysqld.
UPDATE now also works with
BLOB/TEXT columns.
INNER join syntax. NOTE: This made INNER
a reserved word!
IP/NETMASK syntax.
NOT NULL DATE/DATETIME column with IS
NULL, this is changed to a compare against 0 to satisfy some ODBC
applications. (By shreeve@uci.edu).
NULL IN (...) now returns NULL instead of 0. This will
ensure that null_column NOT IN (...) doesn't match
NULL values.
TIME columns.
TIME strings to be more strict. Now the
fractional second part is detected (and currently skipped). The
following formats are supported:
[[DAYS] [H]H:]MM:]SS[.fraction]
[[[[[H]H]H]H]MM]SS[.fraction]
DATETIME.
LOW_PRIORITY attribute to LOAD DATA INFILE.
LOAD DATA INFILE.
DECIMAL(x,y) now works according to ANSI SQL.
LAST_INSERT_ID() is now updated for INSERT INTO ... SELECT.
SELECT DISTINCT is much faster; It uses the new UNIQUE
functionality in MyISAM. One difference compared to MySQL Version 3.22
is that the output of DISTINCT is not sorted anymore.
mysql_num_fields() on
a MYSQL object, you must use mysql_field_count() instead.
LIBEWRAP; Patch by Henning P . Schmiedehausen.
AUTO_INCREMENT for other than numerical columns.
AUTO_INCREMENT will now automatically make the column
NOT NULL.
NULL as the default value for AUTO_INCREMENT columns.
SQL_BIG_RESULT; SQL_SMALL_RESULT is now default.
--enable-large-files/--disable-large-files switch to
configure. See `configure.in' for some systems where this is
automatically turned off because of broken implementations.
readline to 4.0.
CREATE TABLE options: PACK_KEYS and CHECKSUM.
mysqld option --default-table-type.
The 3.22 version has faster and safer connect code and a lot of new nice enhancements. The reason for not including these changes in the 3.21 version is mainly that we are trying to avoid big changes to 3.21 to keep it as stable as possible. As there aren't really any MAJOR changes, upgrading to 3.22 should be very easy and painless. See section 4.17.2 Upgrading from Version 3.21 to Version 3.22.
3.22 should also be used with the new DBD-mysql (1.20xx) driver
that can use the new connect protocol!
STD().
ISAM library from 3.23.
INSERT DELAYED.
LEFT JOIN/STRAIGHT_JOIN
on a table with only one row.
GROUP BY on TINYBLOB columns; This
caused bugzilla to not show rows in some queries.
LOCK TABLE
SELECT DISTINCT queries.
mysqlhotcopy - fast on-line hot-backup utility for local MySQL
databases. By Tim Bunce.
mysqlaccess. Thanks to Steve Harvey for this.
GROUP functions.
ISAM code when deleting rows on tables with
packed indexes.
SELECT when using many overlapping indexes.
SELECT floor(pow(2,63)).
WITH GRANT OPTION option.
GROUP BY queries.
ENUM field value
was too big.
mysqlshutdown.exe and mysqlwatch.exe to the Windows
distribution.
ORDER BY on a reference key.
INSERT DELAYED doesn't update timestamps that are given.
LEFT JOIN and COUNT() on a column which
was declared NULL + and it had a DEFAULT value.
CONCAT() in a WHERE clause.
AVG() and STD() with NULL values.
ROUND() will now work on Windows.
BLOB/TEXT column to REVERSE().
/*! */ with version numbers.
SUBSTRING(text FROM pos) to conform to ANSI SQL. (Before this
construct returned the rightmost 'pos' characters).
LOCK TABLES combined with DELETE FROM table
SET SQL_LOW_PRIORITY_UPDATES=# didn't work.
GRANT ... IDENTIFIED BY
SELECT * FROM table_name WHERE key_part1 >= const AND (key_part2 = const OR key_part2 = const)
DATA is not a reserved word anymore.
LOCK TABLES table_name READ; FLUSH TABLES;
isamchk should now work on Windows.
libtool 1.3.2.
configure.
--defaults-file=### to option file handling to force use
of only one specific option file.
CREATE syntax to ignore MySQL Version 3.23 keywords.
INSERT DELAYED on a table locked with
LOCK TABLES.
DROP TABLE on a table that was
locked by another thread.
GRANT/REVOKE commands in the update log.
isamchk to detect a new error condition.
NATURAL LEFT JOIN.
mysql_close() directly after
mysql_init().
delayed_insert_thread counting when you couldn't create a new
delayed_insert thread.
CONCAT() with many arguments.
DELETE FROM TABLE when table was locked by
another thread.
LEFT JOIN involving empty tables.
mysql.db column from char(32) to char(60).
MODIFY and DELAYED are not reserved words anymore.
TIME column.
Host '...' is not allowed to connect to this MySQL
server after one had inserted a new MySQL user with a GRANT
command.
TCP_NODELAY also on Linux (Should give faster TCP/IP
connections).
STD() for big tables when result should be 0.
INSERT DELAYED had some garbage at end in the update log.
mysql_install_db (from 3.22.17).
BLOB
columns.
shutdown
all threads didn't die properly.
-O flush_time=# to mysqld. This is mostly
useful on Windows and tells how often MySQL should close all
unused tables and flush all updated tables to disk.
VARCHAR column compared with CHAR column
didn't use keys efficiently.
--log-update and connecting
without a default database.
configure and portability problems.
LEFT JOIN on tables that had circular dependencies caused
mysqld to hang forever.
mysqladmin processlist could kill the server if a new user logged in.
DELETE FROM tbl_name WHERE key_column=col_name didn't find any matching
rows. Fixed.
DATE_ADD(column, ...) didn't work.
INSERT DELAYED could deadlock with status 'upgrading lock'
ENCRYPT() to take longer salt strings than 2 characters.
longlong2str is now much faster than before. For Intel x86
platforms, this function is written in optimized assembler.
MODIFY keyword to ALTER TABLE.
GRANT used with IDENTIFIED BY didn't take effect until privileges
were flushed.
SHOW STATUS.
ORDER BY with 'only index' optimization when there
were multiple key definitions for a used column.
DATE and DATETIME columns are now up to 5 times faster than
before.
INSERT DELAYED can be used to let the client do other things while the
server inserts rows into a table.
LEFT JOIN USING (col1,col2) didn't work if one used it with tables
from 2 different databases.
LOAD DATA LOCAL INFILE didn't work in the Unix version because of
a missing file.
VARCHAR/BLOB on very short rows (< 4 bytes);
error 127 could occur when deleting rows.
BLOB/TEXT through formulas didn't work for short (< 256 char)
strings.
GRANT on a new host, mysqld could die on the first
connect from this host.
ORDER BY on column name that was the same
name as an alias.
BENCHMARK(loop_count,expression) function to time expressions.
mysqld to make it easier to start from shell
scripts.
TIMESTAMP column to NULL didn't record the timestamp
value in the update log.
INSERT INTO TABLE ... SELECT ... GROUP BY.
localtime_r() on Windows so that it will not crash
anymore if your date is > 2039, but instead will return a time of all zero.
^Z (ASCII 26) to \Z as ^Z doesn't
work with pipes on Windows.
mysql_fix_privileges adds a new column to the mysql.func to
support aggregate UDF functions in future MySQL releases.
NOW(), CURDATE() or CURTIME() directly in a
column didn't work.
SELECT COUNT(*) ... LEFT JOIN ... didn't work with no WHERE part.
pthread_cond() on the Windows version.
get_lock() now correctly times out on Windows!
DATE_ADD() and DATE_SUB() in a
WHERE clause.
GRANT ... TO user
IDENTIFIED BY 'password' syntax.
GRANT checking with SELECT on many tables.
mysql_fix_privilege_tables to the RPM
distribution. This is not run by default because it relies on the client
package.
SQL_SMALL_RESULT to SELECT to force use of
fast temporary tables when you know that the result set will be small.
DATE_ADD/DATE_SUB() doesn't have enough days.
GRANT compares columns in case-insensitive fashion.
ALTER TABLE dump core in
some contexts.
user@hostname can now include `.' and `-'
without quotes in the context of the GRANT, REVOKE and
SET PASSWORD FOR ... statements.
isamchk for tables which need big temporary files.
mysql_fix_privilege_tables script
when you upgrade to this version! This is needed because of the new
GRANT system. If you don't do this, you will get Access
denied when you try to use ALTER TABLE, CREATE INDEX or
DROP INDEX.
GRANT to allow/deny users table and column access.
USER() to return user@host
PASSWORD for another user.
FLUSH STATUS that sets most status variables to zero.
aborted_threads, aborted_connects.
connection_timeout.
SET SQL_WARNINGS=1 to get a warning count also for simple
inserts.
SIGTERM instead of SIGQUIT with
shutdown to work better on FreeBSD.
\G (print vertically) to mysql.
SELECT HIGH_PRIORITY ... killed mysqld.
IS NULL on a AUTO_INCREMENT column in a LEFT JOIN didn't
work as expected.
MAKE_SET().
mysql_install_db no longer starts the MySQL server! You
should start mysqld with safe_mysqld after installing it! The
MySQL RPM will, however, start the server as before.
--bootstrap option to mysqld and recoded
mysql_install_db to use it. This will make it easier to install
MySQL with RPMs.
+, - (sign and minus), *, /, %,
ABS() and MOD() to be BIGINT aware (64-bit safe).
ALTER TABLE that caused mysqld to crash.
INSERT).
INSERT INTO tbl_name SET col_name=value, col_name=value, ...
MYSQL_INIT_COMMAND to mysql_options() to make
a query on connect or reconnect.
MYSQL_READ_DEFAULT_FILE and
MYSQL_READ_DEFAULT_GROUP to mysql_options() to read the
following parameters from the MySQL option files: port,
socket, compress, password, pipe, timeout,
user, init-command, host and database.
maybe_null to the UDF structure.
IGNORE to INSERT statemants with many rows.
isamchk -rq on each table that has an index on
a CHAR or VARCHAR column.
mysql_setpermission, by Luuk de Boer, allows one
to easily create new users with permissions for specific databases.
LOAD DATA INFILE).
SHOW STATUS and changed format of output to
be like SHOW VARIABLES.
extended-status command to mysqladmin which will show the
new status variables.
SET SQL_LOG_UPDATE=0 caused a lockup of the server.
FLUSH [ TABLES | HOSTS | LOGS | PRIVILEGES ] [, ...]
KILL thread_id.
ALTER TABLE from a INT
to a short CHAR() column.
SELECT HIGH_PRIORITY; This will get a lock for the
SELECT even if there is a thread waiting for another
SELECT to get a WRITE LOCK.
LIKE on
BLOB/TEXT columns with \0.
ESCAPE option to LIKE.
mysqladmin debug.
mysqld on Windows with the --flush option.
This will flush all tables to disk after each update. This makes things
much safer on NT/Win98 but also MUCH slower.
my_strcoll()! The patch should always be safe to install (for any system),
but as this patch changes ISAM internals it's not yet in the default
distribution.
DATE_ADD() and DATE_SUB() didn't work with group functions.
mysql will now also try to reconnect on USE DATABASE commands.
ORDER BY and LEFT JOIN and const tables.
ORDER BY if the first ORDER BY column
was a key and the rest of the ORDER BY columns wasn't part of the key.
OPTIMIZE TABLE.
DROP TABLE and mysqladmin shutdown on Windows
(a fatal bug from 3.22.6).
TIME columns and negative strings.
LIMIT clause for the DELETE statement.
/*! ... */ syntax to hide MySQL-specific
keywords when you write portable code. MySQL will parse the code
inside the comments as if the surrounding /*! and */ comment
characters didn't exist.
OPTIMIZE TABLE tbl_name can now be used to reclaim disk space
after many deletes. Currently, this uses ALTER TABLE to
regenerate the table, but in the future it will use an integrated
isamchk for more speed.
libtool to get the configure more portable.
UPDATE and DELETE operations when using
DATETIME or DATE keys.
mysqladmin proc to display information about your own
threads. Only users with the Process_priv privilege can get
information about all threads.
YYMMDD, YYYYMMDD,
YYMMDDHHMMSS for numbers when using DATETIME and
TIMESTAMP types. (Formerly these formats only worked with strings.)
CLIENT_IGNORE_SPACE to allow use of spaces
after function names and before `(' (Powerbuilder requires this).
This will make all function names reserved words.
--log-long-format option to mysqld to enable timestamps
and INSERT_ID's in the update log.
--where option to mysqldump (patch by Jim Faucette).
mysqldump.
LOAD DATA INFILE statement, you can now use the new LOCAL
keyword to read the file from the client. mysqlimport will
automatically use LOCAL when importing with the TCP/IP protocol.
DROP TABLE, ALTER TABLE, DELETE FROM
TABLE and mysqladmin flush-tables under heavy usage.
Changed locking code to get better handling of locks of different types.
DBI to 1.00 and DBD to 1.2.0.
mysqld. (To avoid errors if you accidentally
try to use an old error message file.)
affected_rows(),
insert_id(), ...) are now of type BIGINT to allow 64-bit values
to be used.
This required a minor change in the MySQL protocol which should affect
only old clients when using tables with AUTO_INCREMENT values > 16M.
mysql_fetch_lengths() has changed from uint *
to ulong *. This may give a warning for old clients but should work
on most machines.
mysys and dbug libraries to allocate all thread variables
in one struct. This makes it easier to make a threaded `libmysql.dll'
library.
gethostname() (instead of uname()) when
constructing `.pid' file names.
COUNT(), STD() and AVG() are extended to handle more than
4G rows.
-838:59:59 <= x <=
838:59:59 in a TIME column.
TIME column to too short a value, MySQL now
assumes the value is given as: [[[D ]HH:]MM:]SS instead of
HH[:MM[:SS]].
TIME_TO_SEC() and SEC_TO_TIME() can now handle negative times
and hours up to 32767.
SET OPTION SQL_LOG_UPDATE={0|1} to allow users with
the process privilege to bypass the update log.
(Modified patch from Sergey A Mukhin violet@rosnet.net.)
LPAD().
BLOB reading from
pipes safer.
-O max_connect_errors=# option to mysqld.
Connect errors are now reset for each correct connection.
max_allowed_packet to 1M in
mysqld.
--low-priority-updates option to mysqld, to give
table-modifying operations (INSERT, REPLACE, UPDATE,
DELETE) lower priority than retrievals. You can now use
{INSERT | REPLACE | UPDATE | DELETE} LOW_PRIORITY ... You can
also use SET OPTION SQL_LOW_PRIORITY_UPDATES={0|1} to change
the priority for one thread. One side effect is that LOW_PRIORITY
is now a reserved word. :(
INSERT INTO table ... VALUES(...),(...),(...),
to allow inserting multiple rows with a single statement.
INSERT INTO tbl_name is now also cached when used with LOCK TABLES.
(Previously only INSERT ... SELECT and LOAD DATA INFILE were
cached.)
GROUP BY functions with HAVING:
mysql> SELECT col FROM table GROUP BY col HAVING COUNT(*)>0;
mysqld will now ignore trailing `;' characters in queries. This
is to make it easier to migrate from some other SQL servers that require the
trailing `;'.
SELECT INTO OUTFILE.
GREATEST() and LEAST() functions. You must now use
these instead of the MAX() and MIN() functions to get the
largest/smallest value from a list of values. These can now handle REAL,
BIGINT and string (CHAR or VARCHAR) values.
DAYOFWEEK() had offset 0 for Sunday. Changed the offset to 1.
GROUP BY columns and fields when
there is no GROUP BY specification.
--vertical option to mysql, for printing results in
vertical mode.
--tmpdir option to mysqld, for specifying the location
of the temporary file directory.
SELECT ... FROM table WHERE auto_increment_column IS NULLto:
SELECT ... FROM table WHERE auto_increment_column == LAST_INSERT_ID()This allows some ODBC programs (Delphi, Access) to retrieve the newly inserted row to fetch the
AUTO_INCREMENT id.
DROP TABLE now waits for all users to free a table before deleting it.
BIN(), OCT(), HEX() and CONV() for
converting between different number bases.
SUBSTRING() with 2 arguments.
ORDER BY and
GROUP BY.
mysqld now automatically disables system locking on Linux and Windows,
and for systems that use MIT-pthreads. You can force the use of locking
with the --enable-locking option.
--console option to mysqld, to force a console window
(for error messages) when using Windows.
DATE_ADD() and DATE_SUB() functions.
mysql_ping() to the client library.
--compress option to all MySQL clients.
byte to char in `mysql.h' and `mysql_com.h'.
<<, >>, RPAD() and LPAD().
ORDER BY to work when no records are found
when using fields that are not in GROUP BY (MySQL extension).
--chroot option to mysqld, to start mysqld in
a chroot environment (by Nikki Chumakov nikkic@cityline.ru).
--one-thread option to mysqld, for debugging with
LinuxThreads (or glibc). (This replaces the -T32 flag)
DROP TABLE IF EXISTS to prevent an error from occurring if the
table doesn't exist.
IF and EXISTS are now reserved words (they would have to
be sooner or later).
mysqldump.
mysql_ping().
mysql_init() and mysql_options().
You now MUST call mysql_init() before you call
mysql_real_connect().
You don't have to call mysql_init() if you only use
mysql_connect().
mysql_options(...,MYSQL_OPT_CONNECT_TIMEOUT,...) so you can set a
timeout for connecting to a server.
--timeout option to mysqladmin, as a test of
mysql_options().
AFTER column and FIRST options to
ALTER TABLE ... ADD columns.
This makes it possible to add a new column at some specific location
within a row in an existing table.
WEEK() now takes an optional argument to allow handling of weeks when
the week starts on Monday (some European countries). By default,
WEEK() assumes the week starts on Sunday.
TIME columns weren't stored properly (bug in MySQL Version 3.22.0).
UPDATE now returns information about how many rows were
matched and updated, and how many ``warnings'' occurred when doing the update.
FORMAT(-100,2).
ENUM and SET columns were compared in binary (case-sensitive)
fashion; changed to be case insensitive.
mysql_real_connect() call is changed to:
mysql_real_connect(MYSQL *mysql, const char *host, const char *user,
const char *passwd, const char *db, uint port,
const char *unix_socket, uint client_flag)
accept() thread. This fixes permanently the telnet bug
that was a topic on the mail list some time ago.
mysqld now has a local hostname
resolver cache so connections should actually be faster than before,
even with this feature.
tbl_name@db_name or db_name.tbl_name. This makes it possible to
give a user read access to some tables and write access to others simply by
keeping them in different databases!
--user option to mysqld, to allow it to run
as another Unix user (if it is started as the Unix root user).
mysqladmin password 'new_password'. This uses encrypted passwords
that are not logged in the normal MySQL log!
SELECT code to handle some very specific queries
involving group functions (like COUNT(*)) without a GROUP BY but
with HAVING. The following now works:
mysql> SELECT count(*) as C FROM table HAVING C > 1;
malloc().
-T32 option to mysqld, for running all queries under the
main thread. This makes it possible to debug mysqld under Linux with
gdb!
not_null_column IS NULL (needed for some Access
queries).
STRAIGHT_JOIN to be used between two tables to force the optimizer
to join them in a specific order.
VARCHAR rather than CHAR and
the column type is now VARCHAR for fields saved as VARCHAR.
This should make the MyODBC driver better, but may break some old
MySQL clients that don't handle FIELD_TYPE_VARCHAR the same
way as FIELD_TYPE_CHAR.
CREATE INDEX and DROP INDEX are now implemented through
ALTER TABLE.
CREATE TABLE is still the recommended (fast) way to create indexes.
--set-variable option wait_timeout to mysqld.
mysqladmin processlist to show how long a query
has taken or how long a thread has slept.
show variables and some new to
show status.
YEAR. YEAR is stored in 1 byte with allowable
values of 0, and 1901 to 2155.
DATE type that is stored in 3 bytes rather than 4 bytes.
All new tables are created with the new date type if you don't use the
--old-protocol option to mysqld.
Error from table handler: # on some operating systems.
--enable-assembler option to configure, for x86 machines
(tested on Linux + gcc). This will enable assembler functions for the
most important string functions for more speed!
SIGHUP to mysqld;
mysqld core dumped when starting from boot on some systems.
DELETE FROM tbl_name without a WHERE condition is now done the
long way when you use LOCK TABLES or if the table is in use, to
avoid race conditions.
INSERT INTO TABLE (timestamp_column) VALUES (NULL); didn't set timestamp.
mysqladmin
refresh often. This could in some very rare cases corrupt the header of the
index file and cause error 126 or 138.
refresh() when running with the
--skip-locking option. There was a ``very small'' time gap after
a mysqladmin refresh when a table could be corrupted if one
thread updated a table while another thread did mysqladmin
refresh and another thread started a new update ont the same table
before the first thread had finished. A refresh (or
--flush-tables) will now not return until all used tables are
closed!
SELECT DISTINCT with a WHERE clause that didn't match any rows
returned a row in some contexts (bug only in 3.21.31).
GROUP BY + ORDER BY returned one empty row when no rows where
found.
Use_count: Wrong count for ... in the error log file.
TINYINT type on Irix.
LEFT("constant_string",function).
FIND_IN_SET().
LEFT JOIN core dumped if the second table is used with a constant
WHERE/ON expression that uniquely identifies one record.
DATE_FORMAT() and incorrect dates.
DATE_FORMAT() now ignores '%' to make it possible to extend
it more easily in the future.
mysql now returns an exit code > 0 if the query returned an error.
mysql client.
By Tommy Larsen tommy@mix.hive.no.
safe_mysqld to redirect startup messages to
'hostname'.err instead
of 'hostname'.log to reclaim file space on mysqladmin refresh.
ENUM always had the first entry as default value.
ALTER TABLE wrote two entries to the update log.
sql_acc() now closes the mysql grant tables after a reload to
save table space and memory.
LOAD DATA to use less memory with tables and BLOB
columns.
SELECT problem with LEFT() when using the czech character
set.
isamchk; it couldn't repair a packed table in a very
unusual case.
SELECT statements with & or | (bit functions) failed on
columns with NULL values.
LOCK TABLES + DELETE from tbl_name never removed locks properly.
OR function.
umask() and creating new databases.
SELECT ... INTO OUTFILE ...
MIN(integer) or MAX(integer) in
GROUP BY.
WEEK("XXXX-xx-01").
Error from table handler: # on some operating systems.
GET_LOCK(string,timeout),
RELEASE_LOCK(string).
opened_tables to show status.
mysqld through telnet + TCP/IP.
WHERE key_part_1 >= something AND key_part_2 <= something_else.
configure for detection of FreeBSD 3.0 9803xx and above
WHERE with string_column_key = constant_string didn't always find
all rows if the column had many values differing only with characters of
the same sort value (like e and 'e).
umask() to make log files non-readable for normal users.
--old-protocol option to mysqld.
SELECT which matched all key fields returned the values in the
case of the matched values, not of the found values. (Minor problem.)
FROM_DAYS(0) now returns "0000-00-00".
DATE_FORMAT(), PM and AM were swapped for hours 00 and 12.
BLOB/TEXT in GROUP BY with many
tables.
ENUM field that is not declared NOT NULL has NULL as
the default value.
(Previously, the default value was the first enumeration value.)
INDEX (Organization,Surname(35),Initials(35)).
SELECT ... FROM many_tables much faster.
accept() to possibly fix some problems on some
Linux machines.
typedef 'string' to typedef 'my_string' for better
portability.
isamchk. Try isamchk --help.
filesort() didn't work.
Affects DISTINCT, ORDER BY and GROUP BY on 64-bit
processors.
SELECT on the
table.
OR operators on key parts
inside each other.
MIN() and MAX() to work properly with strings and
HAVING.
0664 to 0660.
LEFT JOIN and constant expressions in the ON
part.
configure now works better on OSF1 (tested on 4.0D).
LIKE optimization with international character
support.
DBI to 0.93.
TIME, DATE, TIMESTAMP, TEXT, BIT,
ENUM, NO, ACTION, CHECK, YEAR,
MONTH, DAY, HOUR, MINUTE, SECOND,
STATUS, VARIABLES.
TIMESTAMP to NULL in LOAD DATA INFILE ... didn't
set the current time for the TIMESTAMP.
BETWEEN to recognize binary strings. Now BETWEEN is
case sensitive.
--skip-thread-priority option to mysqld, for systems
where mysqld's thread scheduling doesn't work properly (BSDI 3.1).
DAYNAME() and MONTHNAME().
TIME_FORMAT(). This works like DATE_FORMAT(),
but takes a time string ('HH:MM:DD') as argument.
ORs of key parts
inside ANDs.
variables to mysqladmin.
ALTER TABLE to work with Windows (Windows can't rename
open files). Also fixed a couple of small bugs in the Windows version.
crash-me and the benchmarks on
the following platforms: SunOS 5.6 sun4u, SunOS 5.5.1 sun4u, SunOS 4.14 sun4c,
SunOS 5.6 i86pc, Irix 6.3 mips5k, HP-UX 10.20 hppa, AIX 4.2.1 ppc,
OSF1 V4.0 alpha, FreeBSD 2.2.2 i86pc and BSDI 3.1 i386.
COUNT(*) problems when the WHERE clause didn't match any
records. (Bug from 3.21.17.)
NULL = NULL is true. Now you must use IS NULL
or IS NOT NULL to test whether or not a value is NULL.
(This is according to ANSI SQL but may break
old applications that are ported from mSQL.)
You can get the old behavior by compiling with -DmSQL_COMPLIANT.
LEFT OUTER JOIN clauses.
ORDER BY on string formula with possible NULL values.
DAYOFYEAR(), DAYOFMONTH(), MONTH(),
YEAR(), WEEK(), QUARTER(), HOUR(), MINUTE(),
SECOND() and FIND_IN_SET().
SHOW VARIABLES.
mysql> SELECT 'first ' 'second'; -> 'first second'
mysqlaccess to 2.02.
LIKE.
WHERE data_field = date_field2 AND date_field2 = constant.
SHOW STATUS.
mysqladmin stat to return the right number of queries.
AUTO_INCREMENT attribute or is a TIMESTAMP. This is needed for
the new Java driver.
configure bugs and increased maximum table size
from 2G to 4G.
DBD to 1823. This version implements mysql_use_result in
DBD-Mysql.
REVERSE() (by Zeev Suraski).
DBI to 0.91.
LEFT OUTER JOIN.
CROSS JOIN syntax. CROSS is now a reserved word.
yacc/bison stack allocation to be even safer and to allow
MySQL to handle even bigger expressions.
ORDER BY was slow when used with key ranges.
--with-unix-socket-path to avoid
confusion.
LEFT OUTER JOIN.
LEFT, NATURAL,
USING.
MYSQL_HOST as the default host if it's defined.
SELECT col_name, SUM(expr) now returns NULL for col_name
when there are matching rows.
BLOBs with ASCII
characters over 127.
mysqld
restart if one thread was reading data that another thread modified.
LIMIT offset,count didn't work in INSERT ... SELECT.
POWER(), SPACE(),
COT(), DEGREES(), RADIANS(), ROUND(2 arg)
and TRUNCATE().
LOCATE() parameters were
swapped according to ODBC standard. Fixed.
TIME_TO_SEC().
NOT NULL fields.
UPDATE SET ... statements.
BLOB and TEXT, to
be compatible with mysqldump.
mysqlperl is now from
Msql-Mysql-modules. This means that connect() now takes
host, database, user, password arguments! The old
version took host, database, password, user.
DATE '1997-01-01', TIME '12:10:10' and
TIMESTAMP '1997-01-01 12:10:10' formats required by ANSI SQL.
WARNING: INCOMPATIBLE CHANGE!! This has the unfortunate
side-effect that you no longer can have columns named DATE, TIME
or TIMESTAMP. :( Old columns can still be accessed through
tablename.columnname!)
make programs trying to rebuild it.
readline library upgraded to version 2.1.
DBI/DBD is now included in the distribution. DBI
is now the recommended way to connect to MySQL from Perl.
DBD, with test results from
mSQL 2.0.3, MySQL, PostgreSQL 6.2.1 and Solid server 2.2.
crash-me is now included with the benchmarks; This is a Perl program
designed to find as many limits as possible in a SQL server. Tested with
mSQL, PostgreSQL, Solid and MySQL.
mysql command line tool, by Zeev
Suraski and Andi Gutmans.
REPLACE that works like INSERT but
replaces conflicting records with the new record. REPLACE INTO
TABLE ... SELECT ... works also.
CREATE DATABASE db_name and DROP
DATABASE db_name.
RENAME option to ALTER TABLE: ALTER TABLE name
RENAME TO new_name.
make_binary_distribution now includes `libgcc.a' in
`libmysqlclient.a'. This should make linking work for people who don't
have gcc.
net_write() to my_net_write() because of a name
conflict with Sybase.
DAYOFWEEK() compatible with ODBC.
bison memory overrun checking to make MySQL
safer with weird queries.
configure problems on some platforms.
DATE_FORMAT().
NOT IN.
{fn now() }
DATE and TIME values with NULL.
FLOAT. Previously, the
values were converted to INTs before sorting.
key_column=constant.
DOUBLE values sorted on integer results instead.
mysql no longer needs a database argument.
HAVING should be. According to ANSI, it should
be after GROUP BY but before ORDER BY. MySQL Version 3.20
incorrectly had it last.
USE DATABASE to start using another database.
mysqld doesn't crash even if you haven't done a
ulimit -n 256 before starting mysqld.
errno.
This makes Linux systems much safer!
SELECT.
LIKE on number key.
--table option to mysql to print in table format.
Moved time and row information after query result.
Added automatic reconnect of lost connections.
!= as a synonym for <>.
VERSION() to make easier logs.
ftruncate() call in MIT-pthreads. This made isamchk
destroy the `.ISM' files on (Free)BSD 2.x systems.
__P_ patch in MIT-pthreads.
NULL
if the returned string should be longer than max_allowed_packet bytes.
INTERVAL type to ENUM, because
INTERVAL is used in ANSI SQL.
JOIN + GROUP + INTO OUTFILE,
the result wasn't grouped.
LIKE with '_' as last character didn't work. Fixed.
TRIM() function.
CURTIME().
ENCRYPT() function by Zeev Suraski.
FOREIGN KEY syntax skipping. New reserved words:
MATCH, FULL, PARTIAL.
mysqld now allows IP number and hostname to the --bind-address
option.
SET OPTION CHARACTER SET cp1251_koi8 to enable conversions of
data to/from cp1251_koi8.
CREATE COLUMN syntax of NOT NULL columns to be after
the DEFAULT value, as specified in the ANSI SQL standard. This will
make mysqldump with NOT NULL and default values incompatible with
MySQL Version 3.20.
ALTER TABLE tbl_name ALTER COLUMN col_name SET DEFAULT
NULL.
CHAR and BIT as synonyms for CHAR(1).
INSERT ... SELECT ... GROUP BY didn't work in some cases. An
Invalid use of group function error occurred.
LIMIT, SELECT now always uses keys instead of record
scan. This will give better performance on SELECT and a WHERE
that matches many rows.
BIT_OR() and BIT_AND().
CHECK and REFERENCES.
CHECK is now a reserved word.
ALL option to GRANT for better compatibility. (GRANT
is still a dummy function.)
ORDER BY and GROUP BY with NULL columns.
last_insert_id() to retrieve last AUTO_INCREMENT
value. This is intended for clients to ODBC that can't use the
mysql_insert_id() API function, but can be used by any client.
--flush-logs option to mysqladmin.
STATUS to mysql.
ORDER BY/GROUP BY because of bug in gcc.
INSERT ... SELECT ... GROUP BY.
mysqlaccess.
CREATE now supports all ODBC types and the mSQL TEXT type.
All ODBC 2.5 functions are also supported (added REPEAT). This provides
better portability.
TINYTEXT, TEXT, MEDIUMTEXT and
LONGTEXT. These are actually BLOBtypes, but all searching is
done in case-insensitive fashion.
BLOB fields are now TEXT fields. This only
changes that all searching on strings is done in case-sensitive fashion.
You must do an ALTER TABLE and change the field type to BLOB
if you want to have tests done in case-sensitive fashion.
configure issues.
test-select works.
--enable-unix-socket=pathname option to configure.
SUM() functions.
For example, you can now use SUM(column)/COUNT(column).
PI(), ACOS(), ASIN(), ATAN(), COS(),
SIN() and TAN().
net_print() in `procedure.cc'.
SELECT ... INTO OUTFILE syntax.
GROUP BY and SELECT on key with many values.
mysql_fetch_lengths() sometimes returned incorrect lengths when you used
mysql_use_result(). This affected at least some cases of
mysqldump --quick.
WHERE const op field.
NULL fields.
--pid-file=# option to mysqld.
FROM_UNIXTIME(), originally by Zeev Suraski.
BETWEEN in range optimizer (Did only test = of the first
argument).
mysql_errno(), to get the error number of
the error message. This makes error checking in the client much easier.
This makes the new server incompatible with the 3.20.x server when running
without --old-protocol. The client code is backward compatible.
More information can be found in the `README' file!
sigwait and sigset
defines).
configure should now be able to detect the last argument to
accept().
-O tmp_table_size=# to mysqld.
FROM_UNIXTIME(timestamp) which returns a date string in
'YYYY-MM-DD HH:MM:DD' format.
SEC_TO_TIME(seconds) which returns a string in
'HH:MM:SS' format.
SUBSTRING_INDEX(), originally by Zeev Suraski.
mysqld doesn't work on it yet.
pthread_create to work.
mysqld doesn't accept hostnames that start with digits followed by a
'.', because the hostname may look like an IP number.
--skip-networking option to mysqld, to only allow socket
connections. (This will not work with MIT-pthreads!)
free() that killed the server on
CREATE DATABASE or DROP DATABASE.
mysqld -O options to better names.
-O join_cache_size=# option to mysqld.
-O max_join_size=# option to mysqld, to be able to set a
limit how big queries (in this case big = slow) one should be able to handle
without specifying SET OPTION SQL_BIG_SELECTS=1. A # = is about 10
examined records. The default is ``unlimited''.
TIME, DATE, DATETIME or TIMESTAMP
column to a constant, the constant is converted to a time value before
performing the comparison.
This will make it easier to get ODBC (particularly Access97) to work with
the above types. It should also make dates easier to use and the comparisons
should be quicker than before.
query() in
mysqlperl to take a query with \0 in it.
YYMMDD) didn't work.
UPDATE
clause.
SELECT * INTO OUTFILE, which didn't correctly if the outfile already
existed.
mysql now shows the thread ID when starting or doing a reconnect.
--new, but it crashes core a lot yet...
isam library should be relatively 64-bit clean.
isamchk which can detect and fix more problems.
isamlog.
mysqladmin: you can now do mysqladmin kill 5,6,7,8 to kill
multiple threads.
-O backlog=# option to mysqld.
ALTER TABLE now returns warnings from field conversions.
ASCII().
BETWEEN(a,b,c). Use the standard ANSI
synax instead: expr BETWEEN expr AND expr.
SUM() functions.
tbl_name.field_name in UPDATE.
SELECT DISTINCT when using 'hidden group'. For example:
mysql> SELECT DISTINCT MOD(some_field,10) FROM test
GROUP BY some_field;
Note: some_field is normally in the SELECT part. ANSI SQL should
require it.
INTERVAL, EXPLAIN, READ,
WRITE, BINARY.
CHAR(num,...).
IN. This uses a binary search to find a match.
LOCK TABLES tbl_name [AS alias] {READ|WRITE} ...
--log-update option to mysqld, to get a log suitable for
incremental updates.
EXPLAIN SELECT ... to get information about how the
optimizer will do the join.
FIELD_TYPE_TINY_BLOB, FIELD_TYPE_MEDIUM_BLOB,
FIELD_TYPE_LONG_BLOB or FIELD_TYPE_VAR_STRING (as
previously returned by mysql_list_fields). You should instead only use
FIELD_TYPE_BLOB or FIELD_TYPE_STRING. If you want exact
types, you should use the command SHOW FIELDS.
0x###### which can be used as a string
(default) or a number.
FIELD_TYPE_CHAR is renamed to FIELD_TYPE_TINY.
DEFAULT values no longer need to be NOT NULL.
ENUM
SET
double or long long.
This will provide the full 64-bit range with bit functions and fix some
conversions that previously could result in precision losses. One should
avoid using unsigned long long columns with full 64-bit range
(numbers bigger than 9223372036854775807) because calculations are done
with signed long long.
ORDER BY will now put NULL field values first. GROUP BY
will also work with NULL values.
WHERE with expressions.
mysql> SELECT * FROM tbl_name
WHERE key_part_1="customer"
AND key_part_2>=10 AND key_part_2<=10;
Changes from 3.20.18 to 3.20.32b are not documented here because the 3.21 release branched here. And the relevant changes are also documented as changes to the 3.21 version.
-p# (remove # directories from path) to isamlog.
All files are written with a relative path from the database directory
Now mysqld shouldn't crash on shutdown when using the
--log-isam option.
mysqlperl version. It is now compatible with msqlperl-0.63.
DBD module available at http://www.mysql.com/Downloads/Contrib/
site.
STD() (standard deviation).
mysqld server is now compiled by default without debugging
information. This will make the daemon smaller and faster.
--basedir option to
mysqld. All other paths are relative in a normal installation.
BLOB columns sometimes contained garbage when used with a SELECT
on more than one table and ORDER BY.
GROUP BY work as expected
(ANSI SQL extension).
Example:
mysql> SELECT id,id+1 FROM table GROUP BY id;
MYSQL_PWD was reversed. Now MYSQL_PWD is
enabled as default in the default release.
mysqld to core dump with
Arithmetic error on Sparc-386.
--unbuffered option to mysql, for new mysqlaccess.
BLOB columns and the functions IS NULL and
IS NOT NULL in the WHERE clause.
max_allowed_packet is now 64K for
the server and 512K for the client. This is mainly used to catch
incorrect packets that could trash all memory. The server limit may be
changed when it is started.
safe_mysqld to check for running daemon.
ELT() function is renamed to FIELD(). The new
ELT() function returns a value based on an index: FIELD()
is the inverse of ELT() Example: ELT(2,"A","B","C") returns
"B". FIELD("B","A","B","C") returns 2.
COUNT(field), where field could have a NULL value, now
works.
SELECT ... GROUP BY.
WHERE with many unoptimizable brace levels.
get_hostname, only the IP is checked.
Previously, you got Access denied.
INSERT INTO ... SELECT ... WHERE could give the error
Duplicated field.
safe_mysqld to make it ``safer''.
LIKE was case sensitive in some places and case insensitive in others.
Now LIKE is always case insensitive.
'#' anywhere on the line.
SET OPTION SQL_SELECT_LIMIT=#. See the FAQ for more details.
mysqlaccess script.
FROM_DAYS() and WEEKDAY() to also take a full
TIMESTAMP or DATETIME as argument. Before they only took a
number of type YYYYMMDD or YYMMDD.
UNIX_TIMESTAMP(timestamp_column).
mysqld to work around a bug in MIT-pthreads. This makes multiple
small SELECT operations 20 times faster. Now lock_test.pl should
work.
mysql_FetchHash(handle) to mysqlperl.
mysqlbug script is now distributed built to allow for reporting
bugs that appear during the build with it.
getpwuid() instead of
cuserid().
SELECT optimizer when using many tables with the same
column used as key to different tables.
GRANT command to satisfy Powerbuilder.
packets out of order when using MIT-pthreads.
fcntl() fails. Thanks to Mike Bretz for finding this bug.
termbits from `mysql.cc'. This conflicted with
glibc 2.0.
SELECT as superuser without a database.
SELECT with group calculation to outfile.
-p or --password option to mysql without
an argument, the user is solicited for the password from the tty.
MYSQL_PWD (by Elmar Haneke).
kill to mysqladmin to kill a specific
MySQL thread.
AUTO_INCREMENT key with ALTER_TABLE.
AVG() gave too small value on some SELECTs with
GROUP BY and ORDER BY.
DATETIME type (by Giovanni Maruzzelli
maruzz@matrice.it).
DONT_USE_DEFAULT_FIELDS works.
CREATE INDEX.
DATE, TIME and
TIMESTAMP.
OR of multiple tables (gave empty set).
DATE and TIME types.
SELECT with AND-OR levels.
LIMIT and ORDER BY.
ORDER BY and GROUP BY on items that aren't in the
SELECT list.
(Thanks to Wim Bonis bonis@kiss.de, for pointing this out.)
INSERT.
SELECT ... WHERE ... = NULL.
glibc 2.0. To get glibc to work, you should
add the `gibc-2.0-sigwait-patch' before compiling glibc.
ALTER TABLE when changing a NOT NULL field to
allow NULL values.
CREATE TABLE.
CREATE TABLE now allows FLOAT(4) and FLOAT(8) to mean
FLOAT and DOUBLE.
mysqlaccess by Yves.Carlier@rug.ac.be.
This program shows the access rights for a specific user and the grant
rows that determine this grant.
WHERE const op field (by bonis@kiss.de).
SELECT ... INTO OUTFILE, all temporary tables are ISAM
instead of HEAP to allow big dumps.
ALTER TABLE according to SQL92.
--port and --socket options to all utility programs and
mysqld.
readdir_r(). Now mysqladmin create database
and mysqladmin drop database should work.
tempnam(). This should fix the ``sort
aborted'' bug.
sql_update. This fixed slow updates
on first connection. (Thanks to Vaclav Bittner for the test.)
INSERT INTO ... SELECT ...
MEDIUMBLOB fixed.
ALTER TABLE and BLOBs.
SELECT ... INTO OUTFILE now creates the file in the current
database directory.
DROP TABLE now can take a list of tables.
DESCRIBE (DESC).
make_binary_distribution.
configure's
C++ link test.
--without-perl option to configure.
ALTER TABLE didn't copy null bit. As a result, fields that were allowed
to have NULL values were always NULL.
CREATE didn't take numbers as DEFAULT.
ALTER TABLE and multi-part keys.
ALTER TABLE, SELECT ... INTO OUTFILE and
LOAD DATA INFILE.
NOW().
mysql/user table.
add_file_priv which adds the new field file_priv
to the user table. This script must be executed if you want to
use the new SELECT ... INTO and LOAD DATA INFILE ... commands
with a version of MySQL earlier than 3.20.7.
lock_test.pl test fail.
status to mysqladmin for short logging.
-k option to mysqlshow, to get key information for a table.
mysqldump.
configure cannot find a -lpthreads
library.
program --help.
RAND([init]).
sql_lex to handle \0 unquoted, but the client can't send
the query through the C API, because it takes a str pointer.
You must use mysql_real_query() to send the query.
mysql_get_client_info().
mysqld now uses the N_MAX_KEY_LENGTH from `nisam.h' as
the maximum allowed key length.
mysql> SELECT filter_nr,filter_nr FROM filter ORDER BY filter_nr;Previously, this resulted in the error:
Column: 'filter_nr' in order clause is ambiguous.
mysql now outputs '\0', '\t', '\n' and '\\'
when encountering ASCII 0, tab, newline or '\' while writing
tab-separated output.
This is to allow printing of binary data in a portable format.
To get the old behavior, use -r (or --raw).
mysql_fetch_lengths(MYSQL_RES *), which
returns an array of of column lengths (of type uint).
IS NULL in WHERE clause.
SELECT option STRAIGHT_JOIN to tell the optimizer that
it should join tables in the given order.
'--' in `mysql.cc'
(Postgres syntax).
SELECT expressions and table columns in a SELECT
which are not used in the group part. This makes it efficient to implement
lookups. The column that is used should be a constant for each group because
the value is calculated only once for the first row that is found for a group.
mysql> SELECT id,lookup.text,sum(*) FROM test,lookup
WHERE test.id=lookup.id GROUP BY id;
SUM(function) (could cause a core dump).
AUTO_INCREMENT placement in the SQL query:
INSERT into table (auto_field) values (0);inserted 0, but it should insert an
AUTO_INCREMENT value.
mysql now allows doubled '' or "" within strings for
embedded ' or ".
EXP(), LOG(), SQRT(), ROUND(), CEILING().
configure source now compiles a thread-free client library
-lmysqlclient. This is the only library that needs to be linked
with client applications. When using the binary releases, you must
link with -lmysql -lmysys -ldbug -lstrings as before.
readline library from bash-2.0.
configure and makefiles (and related source).
VPATH. Tested with GNU Make 3.75.
safe_mysqld and mysql.server changed to be more compatible
between the source and the binary releases.
LIMIT now takes one or two numeric arguments.
If one argument is given, it indicates the maximum number of rows in
a result. If two arguments are given, the first argument indicates the offset
of the first row to return, the second is the maximum number of rows.
With this it's easy to do a poor man's next page/previous page WWW
application.
FIELDS() to ELT().
Changed SQL function INTERVALL() to INTERVAL().
SHOW COLUMNS a synonym for SHOW FIELDS.
Added compatibility syntax FRIEND KEY to CREATE TABLE. In
MySQL, this creates a non-unique key on the given columns.
CREATE INDEX and DROP INDEX as compatibility functions.
In MySQL, CREATE INDEX only checks if the index exists and
issues an error if it doesn't exist. DROP INDEX always succeeds.
sql_acl (core on new connection).
host, user and db tables from database test
in the distribution.
FIELD_TYPE_CHAR can now be signed (-128 - 127) or unsigned (0 - 255)
Previously, it was always unsigned.
CONCAT() and WEEKDAY().
mysqld to be compiled with SunPro
compiler.
'(' immediately after the function name
(no intervening space).
For example, 'user(' is regarded as beginning a function call, and
'user (' is regarded as an identifier user followed by a
'(', not as a function call.
configure and Automake.
It will make porting much easier. The readline library is included
in the distribution.
DBD will follow when the new DBD code
is ported.
mysqld can now be started with Swedish
or English (default) error messages.
INSERT(), RTRIM(), LTRIM() and
FORMAT().
mysqldump now works correctly for all field types (even
AUTO_INCREMENT). The format for SHOW FIELDS FROM tbl_name
is changed so the Type column contains information suitable for
CREATE TABLE. In previous releases, some CREATE TABLE
information had to be patched when re-creating tables.
BLOB and TIMESTAMP) are corrected.
TIMESTAMP now returns different date information depending on its
create length.
'_'.
DATABASE(), USER(), POW(),
LOG10() (needed for ODBC).
WHERE with an ORDER BY on fields from only one table,
the table is now preferred as first table in a multi-join.
HAVING and IS NULL or IS NOT NULL now works.
SUM(),
AVG()...) didn't work together. Fixed.
mysqldump: Didn't send password to server.
'Locked' to process list as info if a query is
locked by another query.
IF(arg,syntax_error,syntax_error) crashed.
CEILING(), ROUND(), EXP(), LOG() and SQRT().
BETWEEN to handle strings.
SELECT with grouping on BLOB columns not to return
incorrect BLOB info. Grouping, sorting and distinct on BLOB
columns will not yet work as
expected (probably it will group/sort by the first 7 characters in the
BLOB). Grouping on formulas with a fixed string size (use MID()
on a BLOB) should work.
BLOB
fields, the BLOB was garbage on output.
DISTINCT with calculated columns.
The following problems are known and have a very high priority to get fixed:
ANALYZE TABLE on a BDB table may in some case make the table
unusable until one has restarted mysqld. When this happens you will
see errors like the following in the MySQL error file:
001207 22:07:56 bdb: log_flush: LSN past current end-of-log
ALTER TABLE on a BDB table on which you are
running not completed multi-statement transactions. (The transaction
will probably be ignored).
LOCK TABLE .. and FLUSH TABLES .. doesn't
guarantee that there isn't a half-finished transaction in progress on the
table.
The following problems are known and will be fixed in due time:
mysqldump on a MERGE table doesn't include the current
mapped tables.
MATCH only works with SELECT statements.
BLOB values can't ``reliably'' be used in GROUP BY or
ORDER BY or DISTINCT. Only the first max_sort_length
bytes (default 1024) are used when comparing BLOBbs in these cases.
This can be changed with the -O max_sort_length option to
mysqld. A workaround for most cases is to use a substring:
SELECT DISTINCT LEFT(blob,2048) FROM tbl_name.
BIGINT or DOUBLE (both are
normally 64 bits long). It depends on the function which precision one
gets. The general rule is that bit functions are done with BIGINT
precision, IF, and ELT() with BIGINT or DOUBLE
precision and the rest with DOUBLE precision. One should try to
avoid using bigger unsigned long long values than 63 bits
(9223372036854775807) for anything else than bit fields!
BLOB and TEXT columns, automatically
have all trailing spaces removed when retrieved. For CHAR types this
is okay, and may be regarded as a feature according to ANSI SQL92. The bug is
that in MySQL, VARCHAR columns are treated the same way.
ENUM and SET columns in one table.
safe_mysqld re-directs all messages from mysqld to the
mysqld log. One problem with this is that if you execute
mysqladmin refresh to close and reopen the log,
stdout and stderr are still redirected to the old log.
If you use --log extensively, you should edit safe_mysqld to
log to `'hostname'.err' instead of `'hostname'.log' so you can
easily reclaim the space for the old log by deleting the old one and
executing mysqladmin refresh.
UPDATE statement, columns are updated from left to right.
If you refer to a updated column, you will get the updated value instead of the
original value. For example:
mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1will update
KEY with 2 instead of with 1.
select * from temporary_table, temporary_table as t2;
DISTINCT differently if you are using
'hidden' columns in a join or not. In a join, hidden columns are
counted as part of the result (even if they are not shown) while in
normal queries hidden columns doesn't participate in the DISTINCT
comparison. We will probably change this in the future to never compare
the hidden columns when executing DISTINCT
An example of this is:
SELECT DISTINCT mp3id FROM band_downloads WHERE userid = 9 ORDER BY id DESC; and SELECT DISTINCT band_downloads.mp3id, FROM band_downloads,band_mp3 WHERE band_downloads.userid = 9 AND band_mp3.id = band_downloads.mp3id ORDER BY band_downloads.id DESC;In the second case you may in MySQL 3.23.x get two identical rows in the result set (because the hidden 'id' column may differ). Note that the this only happens for queries where you don't have the ORDER BY columns in the result, something that is you are not allowed to do in ANSI SQL.
rollback data, some things
behave a little differently in MySQL than in other SQL servers.
This is just to ensure that MySQL never need to do a rollback
for a SQL command. This may be a little akward at times as column
values must be checked in the application, but this will actually give
you a nice speed increase as it allows MySQL to do some
optimizations that otherwise would be very hard to do.
If you set a column to a wrong value, MySQL will, instead of doing
a rollback, store the best possible value in the column:
NULL into a column that doesn't take
NULL values, MySQL will store 0 or '' (empty
string) in it instead. (This behavior can, however, be changed with the
-DDONT_USE_DEFAULT_FIELDS compile option).
DATE and DATETIME columns. (Like 2000-02-31 or 2000-02-00).
If the date is totally wrong, MySQL will store the special
0000-00-00 date value in the column.
enum to an unsupported value, it will be set to
the error value 'empty string', with numeric value 0.
PROCEDURE on a query that returns an empty set,
in some cases the PROCEDURE will not transform the columns.
MERGE doesn't check if the underlying
tables are of compatible types.
The following are known bugs in earlier versions of MySQL:
DROP TABLE on a table that is
one among many tables that is locked with LOCK TABLES.
LOCK table with WRITE
FLUSH TABLES
UPDATE that updated a key with
a WHERE on the same key may have failed because the key was used to
search for records and the same row may have been found multiple times:
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;A workaround is to use:
mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;This will work because MySQL will not use index on expressions in the
WHERE clause.
For platform-specific bugs, see the sections about compiling and porting.
Everything in this list is in the order it will be done. If you want to affect the priority order, please register a license or support us and tell us what you want to have done more quickly. See section 3 MySQL Licensing and Support.
We plan to make MySQL Version 4.0 a 'quick' release where we only add some new stuff to enable others to help us with developing new features into Version 4.1. The MySQL 4.0 version should only take us about a month to make after which we want to stabilize it and start working on Version 4.1. Version 4.0 should have the following new features:
.frm files) This will enable us
to not run out of bits when adding more table options. One will still
be able to use the old .frm file format with 4.0. All newly created
tables will, however, use the new format.
The new file format will enable us to add new column types, more options
for keys and FOREIGN KEY support.
mysqld as a library. This will have the same interface as the
standard MySQL client (with an extra function to just set up startup
parameters) but will be faster (no TCP/IP or socket overhead), smaller
and much easier to use for embedded products.
One will be able to define at link time if one wants to use the
client/server model or a stand-alone application just by defining which
library to link with.
The mysqld will support all standard MySQL features and
one can use it in a threaded client to run different queries in each
thread.
DELETE FROM table_name will return the number of deleted rows. For
fast execution one should use TRUNCATE table_name.
DELETE (cascading DELETE and multi-table
DELETE.
ORDER BY key_name DESC
queries.
select id from t where grp in (select grp from g where u > 100)
INSERT SQL_CONCURRENT ...; This will force the insert to happen at the
end of the data file if the table is in use by an select to allow
concurrent inserts.
INSERT ... SELECT to use concurrent inserts.
MERGE tables.
SHOW OPEN TABLES
myisampack code into the server.
insert/delete/update so that we
can gracefully recover if the index file gets full.
ALTER TABLE on a table that is symlinked to another
disk, create temporary tables on this disk.
MyISAM)
without threads.
DECRYPT().
INSERT SQL_CONCURRENT and mysqld --concurrent-insert to do
a concurrent insert at the end of the file if the file is read-locked.
FOREIGN key definitions in the `.frm' file.
lockd works with modern Linux kernels; If not, we have
to fix lockd! To test this, start mysqld with
--enable-locking and run the different fork* test suits. They shouldn't
give any errors if lockd works.
LIMIT, like in LIMIT @a,@b.
DEFAULT values to columns. Give an error when using
an INSERT that doesn't contain a column that doesn't have a
DEFAULT.
SELECT CACHED ...
mysql_query() commands in a row
without reading results or give a nice error message when one does this.
BIT type to take 1 bit (now BIT takes 1 char).
ctime() doesn't work on some FreeBSD systems.
ORDER BY to UPDATE. This would be handy with functions like:
generate_id(start,step).
IMAGE option to LOAD DATA INFILE to not update
TIMESTAMP and AUTO_INCREMENT fields.
LOAD DATA INFILE understand syntax like:
LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name TEXT_FIELDS (text_field1, text_field2, text_field3) SET table_field1=concatenate(text_field1, text_field2), table_field3=23 IGNORE text_field3 This can be used to skip over extra columns in the text file, or update columns based on expressions of the read data...
LOAD DATA INFILE 'file_name' INTO TABLE 'table_name' ERRORS TO err_table_name
This would cause any errors and warnings to be logged into the err_table_name
table. That table would have a structure like:
line_number - line number in data file error_message - the error/warning message and maybe data_line - the line from the data file
VARCHAR support (There is already support for this in MyISAM).
mysql to netscape.
LOCK DATABASES. (with various options)
DECIMAL and NUMERIC types can't read exponential numbers;
Field_decimal::store(const char *from,uint len) must be recoded
to fix this.
mysql.cc to do fewer malloc() calls when hashing field
names.
t1 JOIN t2 ON ... and t1 JOIN t2 USING ...
Currently, you can only use this syntax with LEFT JOIN.
unsigned long long type.
CASE.
show status. Counts for:
INSERT/DELETE/UPDATE statements. Records reads and
updated. Selects on 1 table and selects with joins. Mean number of
tables in select. Number of ORDER BY and GROUP BY queries.
mysql in the middle of a query, you should open
another connection and kill the old running query.
Alternatively, an attempt should be made to detect this in the server.
SHOW INFO FROM tbl_name for basic table information
should be implemented.
NATURAL JOIN and UNION JOIN
select a from crash_me left join crash_me2 using (a); In this
case a is assumed to come from the crash_me table.
ON and USING works with the JOIN and
INNER JOIN join types.
CONNECT BY PRIOR ... to search hierarchy structures.
RENAME DATABASE
mysqladmin copy database new-database. -- Requires COPY command to be
added to mysqld
SHOW HOSTS for printing information about the hostname cache.
DELETE and REPLACE options to the UPDATE statement
(this will delete rows when one gets a duplicate key error while updating).
DATETIME to store fractions of seconds.
NULL for calculated columns.
SELECT COUNT(*)*(id+0) FROM table_name GROUP BY id
ALTER TABLE doesn't abort clients that executes
INSERT DELAYED.
UPDATE clause contains the old
values before the update started.
UPDATE statements. For example:
UPDATE TABLE foo SET @a=a+b,a=@a, b=@a+c
myisamchk, REPAIR and OPTIMIZE TABLE should be able
to handle cases where the data and/or index files are symbolic links.
pread()/pwrite() on windows to enable
concurrent inserts.
SUM(DISTINCT)
ANY(),EVERY() and SOME() group functions. In
ANSI SQL these only works on boolean columns, but we can extend these to
work on any columns/expressions by applying: value == 0 -> FALSE and
value <> 0 -> TRUE.
MAX(column) is the same as the column type.
create table t1 (a DATE); insert into t1 values (now()); create table t2 select max(a) from t1; show columns from t2;
UPDATE the row
if it exists and INSERT a new row if the row didn't exist.
(Like REPLACE works with INSERT / DELETE)
get_changed_tables(timeout,table1,table2,...)
update items,month set
items.price=month.price where items.id=month.id;;
SHOW commands.
SET TIMESTAMP=#;
UNION, MINUS, INTERSECT and FULL OUTER JOIN.
(Currently only LEFT OUTER JOIN is supported)
UNIQUE on fields that can be NULL.
SQL_OPTION MAX_SELECT_TIME=# to put a time limit on a query.
LIMIT to retrieve data from the end.
safe_mysqld: according to FSSTND (which
Debian tries to follow) PID files should go into `/var/run/<progname>.pid'
and log files into `/var/log'. It would be nice if you could put the
"DATADIR" in the first declaration of "pidfile" and "log", so the
placement of these files can be changed with a single statement.
zlib() for gzip-ed files to LOAD DATA INFILE.
BLOB columns (partly solved now).
AUTO_INCREMENT value when one sets a column to 0.
Use NULL instead.
JOIN with parentheses.
GET_LOCK. When doing this,
one must also handle the possible deadlocks this change will introduce.
Time is given according to amount of work, not real time.
A working Posix thread library is needed for the server. On Solaris 2.5 we use Sun PThreads (the native thread support in 2.4 and earlier versions are not good enough) and on Linux we use LinuxThreads by Xavier Leroy, Xavier.Leroy@inria.fr.
The hard part of porting to a new Unix variant without good native thread support is probably to port MIT-pthreads. See `mit-pthreads/README' and Programming POSIX Threads.
The MySQL distribution includes a patched version of Provenzano's Pthreads from MIT (see MIT Pthreads web page). This can be used for some operating systems that do not have POSIX threads.
It is also possible to use another user level thread package named FSU Pthreads (see FSU Pthreads home page). This implementation is being used for the SCO port.
See the `thr_lock.c' and `thr_alarm.c' programs in the `mysys' directory for some tests/examples of these problems.
Both the server and the client need a working C++ compiler (we use gcc
and have tried SparcWorks). Another compiler that is known to work is the
Irix cc.
To compile only the client use ./configure --without-server.
There is currently no support for only compiling the server, nor is it likly to be added unless someone has a good reason for it.
If you want/need to change any `Makefile' or the configure script you must
get Automake and Autoconf. We have used the automake-1.2 and
autoconf-2.12 distributions.
All steps needed to remake everything from the most basic files.
/bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug --prefix='your installation directory' # The makefiles generated above need GNU make 3.75 or newer. # (called gmake below) gmake clean all install init-db
If you run into problems with a new port, you may have to do some debugging of MySQL! See section H.1 Debugging a MySQL server.
NOTE: Before you start debugging mysqld, first get the test
programs mysys/thr_alarm and mysys/thr_lock to work. This
will ensure that your thread installation has even a remote chance to work!
If you are using some functionality that is very new in MySQL,
you can try to run mysqld with the --skip-new (which will disable all
new, potentially unsafe functionality) or with --safe-mode which
disables a lot of optimization that may cause problems.
See section 20.2 What to Do if MySQL Keeps Crashing.
If mysqld doesn't want to start, you should check that you don't have
any my.cnf files that interfere with your setup!
You can check your my.cnf arguments with mysqld --print-defaults
and avoid using them by starting with mysqld --no-defaults ....
If you have some very specific problem, you can always try to debug
MySQL. To do this you must configure MySQL with the
option --with-debug. You can check whether or not
MySQL was compiled with debugging by doing: mysqld
--help. If the --debug flag is listed with the options then you
have debugging enabled. mysqladmin ver also lists the
mysqld version as mysql ... -debug in this case.
If you are using gcc or egcs, the recommended configure line is:
CC=gcc CFLAGS="-O6" CXX=gcc CXXFLAGS="-O6 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-debug --with-extra-charsets=complex
This will avoid problems with the libstdc++ library and with C++
exceptions (many compilers have problems with C++ exceptions in threaded
code) and compile a MySQL version with support for all character sets.
If mysqld stops crashing when you compile it with
--with-debug, you have probably found a compiler bug or a timing
bug within MySQL. In this case you can try to add -g to
the CFLAGS and CXXFLAGS variables above and not use
--with-debug. If mysqld now dies, you can at least attach
to it with gdb or use gdb on the core file to find out
what happened.
If you can cause the mysqld server to crash quickly, you can try to
create a trace file of this:
Start the mysqld server with a trace log in `/tmp/mysql.trace'.
The log file will get very BIG.
mysqld --debug --log
or you can start it with
mysqld --debug=d,info,error,query,general,where:O,/tmp/mysql.trace
which only prints information with the most interesting tags.
When you configure MySQL for debugging you automatically enable a
lot of extra safety check functions that monitor the health of mysqld.
If they find something ``unexpected,'' an entry will be written to
stderr, which safe_mysqld directs to the error log! This also
means that if you are having some unexpected problems with MySQL and
are using a source distribution, the first thing you should do is to
configure MySQL for debugging! (The second thing, of course, is to
send mail to mysql@lists.mysql.com and ask for help. Please use the
mysqlbug script for all bug reports or questions regarding the
MySQL version you are using!
On most system you can also start mysqld from gdb to get
more information if mysqld crashes.
With some older gdb versions on Linux you must use run
--one-thread if you want to be able to debug mysqld threads. In
this case you can only have one thread active at a time.
It's very hard to debug MySQL under gdb if you do a lot of
new connections the whole time as gdb doesn't free the memory for
old threads. You can avoid this problem by starting mysqld with
-O thread_cache_size= 'max_connections +1'. In most cases just
using -O thread_cache_size= 5' will help a lot!
If you want to get a core dump on Linux if mysqld dies with a
SIGSEGV signal, you can start mysqld with the --core-file option.
This core file can be used to make a backtrace that may help you
find out why mysqld died:
shell> gdb mysqld core gdb> backtrace gdb> info local gdb> exit
See section 20.2 What to Do if MySQL Keeps Crashing.
If you are using gdb 4.17.x or above on Linux, you should install a `.gdb' file, with the following information, in your current directory:
set print sevenbit off handle SIGUSR1 nostop noprint handle SIGUSR2 nostop noprint handle SIGWAITING nostop noprint handle SIGLWP nostop noprint handle SIGPIPE nostop handle SIGALRM nostop handle SIGHUP nostop handle SIGTERM nostop noprint
If you have problems debugging threads with gdb, you should download gdb 5.x and try this instead. The new gdb version has very improved thread handling!
Here is an example how to debug mysqld:
shell> gdb /usr/local/libexec/mysqld gdb> run ... back # Do this when mysqld crashes info locals up info locals up ... (until you get some information about local variables) quit
Include the above output in a mail generated with mysqlbug and
mail this to mysql@lists.mysql.com.
If mysqld hangs you can try to use some system tools like
strace or /usr/proc/bin/pstack to examine where
mysqld has hung.
strace /tmp/log libexec/mysqld
If mysqld starts to eat up CPU or memory or if it ``hangs'', you
can use mysqladmin processlist status to find out if someone is
executing a query that takes a long time. It may be a good idea to
run mysqladmin -i10 processlist status in some window if you are
experiencing performance problems or problems when new clients can't connect.
If mysqld dies or hangs, you should start mysqld with
--log. When mysqld dies again, you can check in the log
file for the query that killed mysqld. Note that before starting
mysqld with --log you should check all your tables with
myisamchk. See section 15 Maintaining a MySQL Installation.
If you are using a log file, mysqld --log, you should check the
'hostname' log files, that you can find in the database directory, for
any queries that could cause a problem. Try the command EXPLAIN
on all SELECT statements that takes a long time to ensure that
mysqld are using indexes properly. See section 7.29 EXPLAIN Syntax (Get Information About a SELECT). You
should also test complicated queries that didn't complete within the
mysql command line tool.
You can find the queries that take a long time to execute by starting
mysqld with --log-slow-queries. See section 21.5 The Slow Query Log.
If you find the text mysqld restarted in the error log file
(normally named `hostname.err') you have probably found a query
that causes mysqld to fail. If this happens you should check all
your tables with myisamchk (see section 15 Maintaining a MySQL Installation), and test the
queries in the MySQL log files to see if one doesn't work. If
you find such a query, try first upgrading to the newest MySQL
version. If this doesn't help and you can't find anything in the
mysql mail archive, you should report the bug to
mysql@lists.mysql.com. Links to mail archives are available
online at the MySQL
documentation page.
If you get corrupted tables or if mysqld always fails after some
update commands, you can test if this bug is reproducible by doing the
following:
mysqladmin shutdown)
myisamchk -s database/*.MYI. Repair any
wrong tables with myisamchk -r database/table.MYI.
mysqld with --log-update. See section 21.3 The Update Log.
mysqld server.
mysqld server without --log-update
mysql < update-log. The update log
is saved in the MySQL database directory with the name
your-hostname.#.
ISAM code! FTP the tables and the update log to
ftp://support.mysql.com/pub/mysql/secret and we will fix this as soon as
possible!
The command mysqladmin debug will dump some information about
locks in use, used memory and query usage to the mysql log file. This
may help solve some problems. This command also provides some useful
information even if you haven't compiled MySQL for debugging!
If the problem is that some tables are getting slower and slower you
should try to optimize the table with OPTIMIZE TABLE or
myisamchk. See section 15 Maintaining a MySQL Installation. You should also check the slow
queries with EXPLAIN.
You should also read the OS-specific section in this manual for problems that may be unique to your environment. See section 4.12 System-specific Issues.
If you are using the Perl DBI interface, you can turn on
debugging information by using the trace method or by
setting the DBI_TRACE environment variable.
See section 22.5.2 The DBI Interface.
To be able to debug a MySQL client with the integrated debug package,
you should configure MySQL with --with-debug.
See section 4.7.3 Typical configure Options.
Before running a client, you should set the MYSQL_DEBUG environment
variable:
shell> MYSQL_DEBUG=d:t:O,/tmp/client.trace shell> export MYSQL_DEBUG
This causes clients to generate a trace file in `/tmp/client.trace'.
If you have problems with your own client code, you should attempt to
connect to the server and run your query using a client that is known to
work. Do this by running mysql in debugging mode (assuming you
have compiled MySQL with debugging on):
shell> mysql --debug=d:t:O,/tmp/client.trace
This will provide useful information in case you mail a bug report. See section 2.3 How to Report Bugs or Problems.
If your client crashes at some 'legal' looking code, you should check that your `mysql.h' include file matches your mysql library file. A very common mistake is to use an old `mysql.h' file from an old MySQL installation with new MySQL library.
The MySQL server and most MySQL clients are compiled with the DBUG package originally made by Fred Fish. When one has configured MySQL for debugging, this package makes it possible to get a trace file of what the program is debugging.
One uses the debug package by invoking the program with the
--debug="..." or the -#... option.
The debug control string is a sequence of colon separated fields as follows:
<field_1>:<field_2>:...:<field_N>
Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:
flag[,modifier,modifier,...,modifier]
The currently recognized flag characters are:
| d | Enable output from DBUG_<N> macros for for the current state. May be followed by a list of keywords which selects output only for the DBUG macros with that keyword. A empty list of keywords implies output for all macros. |
| D | Delay after each debugger output line. The argument is the number of tenths of seconds to delay, subject to machine capabilities. That is, -#D,20 is delay two seconds.
|
| f | Limit debugging and/or tracing, and profiling to the list of named functions. Note that a null list will disable all functions. The appropriate "d" or "t" flags must still be given, this flag only limits their actions if they are enabled. |
| F | Identify the source file name for each line of debug or trace output. |
| i | Identify the process with the pid or thread id for each line of debug or trace output. |
| g | Enable profiling. Create a file called 'dbugmon.out' containing information that can be used to profile the program. May be followed by a list of keywords that select profiling only for the functions in that list. A null list implies that all functions are considered. |
| L | Identify the source file line number for each line of debug or trace output. |
| n | Print the current function nesting depth for each line of debug or trace output. |
| N | Number each line of dbug output. |
| o | Redirect the debugger output stream to the specified file. The default output is stderr. |
| O | As O but the file is really flushed between each write. When neaded the file is closed and reopened between each write.
|
| p | Limit debugger actions to specified processes. A process must be identified with the DBUG_PROCESS macro and match one in the list for debugger actions to occur. |
| P | Print the current process name for each line of debug or trace output. |
| r | When pushing a new state, do not inherit the previous state's function nesting level. Useful when the output is to start at the left margin. |
| S | Do function _sanity(_file_,_line_) at each debugged function until _sanity() returns something that differs from 0. (Mostly used with safemalloc to find memory leaks) |
| t | Enable function call/exit trace lines. May be followed by a list (containing only one modifier) giving a numeric maximum trace level, beyond which no output will occur for either debugging or tracing macros. The default is a compile time option. |
Some examples of debug control strings which might appear on a shell command line (the "-#" is typically used to introduce a control string to an application program) are:
-#d:t -#d:f,main,subr1:F:L:t,20 -#d,input,output,files:n -#d:t:i:O,\\mysqld.trace
In MySQL, common tags to print (with the d option) are:
enter,exit,error,warning,info and
loop.
Currently MySQL only supports table locking for
ISAM/MyISAM and HEAP tables and page level locking
for BDB tables. See section 12.2.8 How MySQL Locks Tables. With MyISAM
tables one can freely mix INSERT and SELECT without locks
(Versioning).
Some database users claim that MySQL cannot support near the number of concurrent users because it lacks row-level locking. This is a may be true for some specific applications, but is' not generally true. As always this depends totally on what the application does and what is the access/update pattern of the data.
Pros for row locking:
Cons:
GROUP
BY on a large part of the data or if one has to often scan the whole table.
Table locks are superior to page level / row level locks in the following cases:
UPDATE table_name SET column=value WHERE unique_key# DELETE FROM table_name WHERE unique_key=#
SELECT combined with INSERT (and very few UPDATE's
and DELETE's.
GROUP BY on the whole table without any writers.
Other options than row / page level locking:
Versioning (like we use in MySQL for concurrent inserts) where you can have one writer at the same time as many readers. This means that the database/table supports different views for the data depending on when one started to access it. Other names for this are time travel, copy on write or copy on demand.
Copy on demand is in many case much better than page or row level locking; The worst case does, however, use much more memory than when using normal locks.
Instead of using row level locks one can use application level locks. (Like get_lock/release_lock in MySQL). This works of course only in well-behaved applications.
In many cases one can do an educated guess which locking type is best for the application but generally it's very hard to say that a given lock type is better than another; Everything depends on the application and different part of the application may require different lock types.
Here are some tips about locking in MySQL:
On web application most applications do lots of selects, very few deletes, updates mainly on keys and inserts in some specific tables. The base MySQL setup is VERY tuned for this.
Concurrent users is not a problem if one doesn't mix updates and selects that needs to examine many rows in the same table.
If one mix a insert and deletes on the same table then INSERT DELAY
may be of great help.
One can also use LOCK TABLES to speed up things (many updates within
a single lock is much faster than updates without locks). Splitting
thing to different tables will also helps.
If you get speed problems with the table locks in MySQL, you
may be able to solve these to convert some of your tables to BDB tables.
See section 8.5 BDB or Berkeley_db Tables.
The optimization section in the manual covers a lot of different aspects of how to tune ones application. See section 12.6 Other Optimization Tips.
I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:
They use an old version of a lot of POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification.
Some wrappers are already written. See `mysys/my_pthread.c' for more info.
At least the following should be changed:
pthread_get_specific should use one argument.
sigwait should take two arguments.
A lot of functions (at least pthread_cond_wait,
pthread_cond_timedwait)
should return the error code on error. Now they return -1 and set errno.
Another problem is that user-level threads use the ALRM signal and this
aborts a lot of functions (read, write, open...).
MySQL should do a retry on interrupt on all of these but it is
not that easy to verify it.
The biggest unsolved problem is the following:
To get thread-level alarms I changed `mysys/thr_alarm.c' to wait between
alarms with pthread_cond_timedwait(), but this aborts with error
EINTR. I tried to debug the thread library as to why this happens,
but couldn't find any easy solution.
If someone wants to try MySQL with RTS threads I suggest the following:
-DHAVE_rts_threads.
thr_alarm.
thr_alarm. If it runs without any ``warning'', ``error'' or aborted
messages, you are on the right track. Here is a successful run on
Solaris:
Main thread: 1 Tread 0 (5) started Thread: 5 Waiting process_alarm Tread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end
MySQL is very dependent on the thread package used. So when choosing a good platform for MySQL, the thread package is very important.
There are at least three types of thread packages:
ps may show the different threads. If one thread aborts, the
whole process aborts. Most system calls are thread safe and should
require very little overhead. Solaris, HP-UX, AIX and OSF1 have kernel
threads.
In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn't really ``thread aware''.
A regular expression (regex) is a powerful way of specifying a complex search.
MySQL uses Henry Spencer's implementation of regular expressions, which is aimed to conform to POSIX 1003.2. MySQL uses the extended version.
This is a simplistic reference that skips the details. To get more exact
information, see Henry Spencer's regex(7) manual page that is
included in the source distribution. See section D Credits.
A regular expression describes a set of strings. The simplest regexp is
one that has no special characters in it. For example, the regexp
hello matches hello and nothing else.
Non-trivial regular expressions use certain special constructs so that
they can match more than one string. For example, the regexp
hello|word matches either the string hello or the string
word.
As a more complex example, the regexp B[an]*s matches any of the
strings Bananas, Baaaaas, Bs and any other string
starting with a B, ending with an s, and containing any
number of a or n characters in between.
A regular expression may use any of the following special characters/constructs:
^
mysql> select "fo\nfo" REGEXP "^fo$"; -> 0 mysql> select "fofo" REGEXP "^fo"; -> 1
$
mysql> select "fo\no" REGEXP "^fo\no$"; -> 1 mysql> select "fo\no" REGEXP "^fo$"; -> 0
.
mysql> select "fofo" REGEXP "^f.*"; -> 1 mysql> select "fo\nfo" REGEXP "^f.*"; -> 1
a*
a characters.
mysql> select "Ban" REGEXP "^Ba*n"; -> 1 mysql> select "Baaan" REGEXP "^Ba*n"; -> 1 mysql> select "Bn" REGEXP "^Ba*n"; -> 1
a+
a characters.
mysql> select "Ban" REGEXP "^Ba+n"; -> 1 mysql> select "Bn" REGEXP "^Ba+n"; -> 0
a?
a character.
mysql> select "Bn" REGEXP "^Ba?n"; -> 1 mysql> select "Ban" REGEXP "^Ba?n"; -> 1 mysql> select "Baan" REGEXP "^Ba?n"; -> 0
de|abc
de or abc.
mysql> select "pi" REGEXP "pi|apa"; -> 1 mysql> select "axe" REGEXP "pi|apa"; -> 0 mysql> select "apa" REGEXP "pi|apa"; -> 1 mysql> select "apa" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pi" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pix" REGEXP "^(pi|apa)$"; -> 0
(abc)*
abc.
mysql> select "pi" REGEXP "^(pi)*$"; -> 1 mysql> select "pip" REGEXP "^(pi)*$"; -> 0 mysql> select "pipi" REGEXP "^(pi)*$"; -> 1
{1}
{2,3}
a*
a{0,}.
a+
a{1,}.
a?
a{0,1}.
i and no comma matches a sequence of exactly i matches of
the atom. An atom followed by a bound containing one integer i
and a comma matches a sequence of i or more matches of the atom.
An atom followed by a bound containing two integers i and
j matches a sequence of i through j (inclusive)
matches of the atom.
Both arguments must 0 >= value <= RE_DUP_MAX (default 255).
If there are two arguments, the second must be greater than or equal to the
first.
[a-dX]
[^a-dX]
a, b,
c, d or X. To include a literal ] character,
it must immediately follow the opening bracket [. To include a
literal - character, it must be written first or last. So
[0-9] matches any decimal digit. Any character that does not have
a defined meaning inside a [] pair has no special meaning and
matches only itself.
mysql> select "aXbc" REGEXP "[a-dXYZ]"; -> 1 mysql> select "aXbc" REGEXP "^[a-dXYZ]$"; -> 0 mysql> select "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1 mysql> select "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0 mysql> select "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1 mysql> select "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0
[[.characters.]]
ch
collating element, then the regular expression [[.ch.]]*c matches the
first five characters of chchcc.
[=character_class=]
o and (+) are the members of an
equivalence class, then [[=o=]], [[=(+)=]], and
[o(+)] are all synonymous. An equivalence class may not be an
endpoint of a range.
[:character_class:]
[: and :] stands for the list of all characters belonging
to that class. Standard character class names are:
| alnum | digit | punct |
| alpha | graph | space |
| blank | lower | upper |
| cntrl | xdigit |
ctype(3) manual
page. A locale may provide others. A character class may not be used as an
endpoint of a range.
mysql> select "justalnums" REGEXP "[[:alnum:]]+"; -> 1 mysql> select "!!" REGEXP "[[:alnum:]]+"; -> 0
[[:<:]]
[[:>:]]
ctype(3)) or an underscore
(_).
mysql> select "a word a" REGEXP "[[:<:]]word[[:>:]]"; -> 1 mysql> select "a xword a" REGEXP "[[:<:]]word[[:>:]]"; -> 0
mysql> select "weeknights" REGEXP "^(wee|week)(knights|nights)$"; -> 1
Unireg is our tty interface builder, but it uses a low-level connection to our ISAM (which is used by MySQL) and because of this it is very quick. It has existed since 1979 (on Unix in C since ~1986).
Unireg has the following components:
convform utility. Converts `.frm' and text files between
different character sets.
myisampack utility. Packs an ISAM table (makes it 50-80%
smaller). The table can be read by MySQL like an ordinary
table. Only one record has to be decompressed per access. Cannot handle
BLOB or TEXT columns or updates (yet).
We update most of our production databases with the Unireg interface and serve web pages through MySQL (and in some extreme cases the Unireg report generator).
Unireg takes about 3M of disk space and works on at least the following platforms: SunOS 4.x, Solaris, Linux, HP-UX, ICL Unix, DNIX, SCO and MS-DOS.
Unireg is currently only available in Swedish and Finnish.
The price tag for Unireg is 10,000 Swedish kr (about $1500 US), but this includes support. Unireg is distributed as a binary. (But all the ISAM sources can be found in MySQL). Usually we compile the binary for the customer at their site.
All new development is concentrated to MySQL.
GNU GENERAL PUBLIC LICENSE Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. GNU GENERAL PUBLIC LICENSE TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you". Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does. 1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee. 2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License. c) If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License. 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: a) Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, c) Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code. 4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. 5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it. 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. 7. 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If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. NO WARRANTY 11. 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IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. END OF TERMS AND CONDITIONS Appendix: How to Apply These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. <one line to give the program's name and a brief idea of what it does.> Copyright (C) 19yy <name of author> This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. <signature of Ty Coon>, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
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Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the library, or if you modify it. For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link a program with the library, you must provide complete object files to the recipients so that they can relink them with the library, after making changes to the library and recompiling it. And you must show them these terms so they know their rights. Our method of protecting your rights has two steps: (1) copyright the library, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the library. Also, for each distributor's protection, we want to make certain that everyone understands that there is no warranty for this free library. If the library is modified by someone else and passed on, we want its recipients to know that what they have is not the original version, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. 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See the GNU Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. Also add information on how to contact you by electronic and paper mail. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the library, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker. <signature of Ty Coon>, 1 April 1990 Ty Coon, President of Vice That's all there is to it!
mysql_affected_rows()
mysql_change_user()
mysql_character_set_name()
mysql_close()
mysql_connect()
mysql_create_db()
mysql_data_seek()
mysql_debug()
mysql_drop_db()
mysql_dump_debug_info()
mysql_eof()
mysql_errno()
mysql_error()
mysql_escape_string()
mysql_fetch_field()
mysql_fetch_field_direct()
mysql_fetch_fields()
mysql_fetch_lengths()
mysql_fetch_row()
mysql_field_count(), mysql_field_count()
mysql_field_seek()
mysql_field_tell()
mysql_free_result()
mysql_get_client_info()
mysql_get_host_info()
mysql_get_proto_info()
mysql_get_server_info()
mysql_info()
mysql_init()
mysql_insert_id()
mysql_kill()
mysql_list_dbs()
mysql_list_fields()
mysql_list_processes()
mysql_list_tables()
mysql_num_fields()
mysql_num_rows()
mysql_options()
mysql_ping()
mysql_query(), mysql_query()
mysql_real_connect()
mysql_real_escape_string()
mysql_real_query()
mysql_reload()
mysql_row_seek()
mysql_row_tell()
mysql_select_db()
mysql_shutdown()
mysql_stat()
mysql_store_result(), mysql_store_result()
mysql_thread_id()
mysql_use_result()
GROUP BY clauses
ORDER BY clauses
AUTO_INCREMENT, and NULL values
BDB table type
BDB tables
Berkeley_db table type
Binlog_Dump
BLOB columns, default values
BLOB columns, indexing
BLOB, inserting binary data
mysqld server
cc1plus problems
config.cache file
configure script
configure, running after prior invocation
Contrib directory
db table, sorting
DBI interface
DBI Perl module
DBI/DBD
BLOB and TEXT columns
mysql.sock
SHOW
myisamchk output
fatal signal 11
config.cache
tmp
my.cnf
SELECT and WHERE clauses
GROUP BY, aliases in
HEAP table type
host table
host table, sorting
BLOB columns
IS NULL
LIKE
NULL values
TEXT columns
mysqlclient
make_binary_distribution
MERGE table type
msql2mysql
my.cnf file
myisamchk, myisamchk
myisamchk, example output
myisamchk, options
myisampack, myisampack
mysiamchk
mysladmn
mysql
mysql.sock, protection
mysql_fix_privilege_tables
mysql_install_db
mysql_install_db script
mysqlaccess
mysqladmin, mysqladmin, mysqladmin, mysqladmin, mysqladmin, mysqladmin
mysqlbug
mysqlbug script
mysqlbug script, location
mysqlclient library
mysqld
mysqld options
mysqld server, buffer sizes
mysqld, starting
mysqld_multi
mysqldump, mysqldump, mysqldump
mysqlimport, mysqlimport, mysqlimport, mysqlimport
mysqlshow
mysql.user table
NULL values, and indexes
NULL values, vs. empty values
NULL values, and AUTO_INCREMENT columns
NULL values, and TIMESTAMP columns
myisamchk
ORDER BY, aliases in
pack_isam
DATE columns
replace
configure after prior invocation
safe-mode command
safe_mysqld
mysql_install_db
mysqlbug
sql_yacc.cc problems
mysqld
BDB
HEAP
host
TEXT columns, default values
TEXT columns, indexing
TIMESTAMP, and NULL values
user table, sorting
mysqld
mysql.columns_priv table
mysql.db table
mysql.host table
mysql.tables_priv table
LIKE
mysql.user table
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