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 There is a very good chance that this version is out of date, unless you are looking at it online.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 d