The MySQL (R) software delivers a very fast, multi-threaded, multi-user, and robust SQL (Structured Query Language) database server. MySQL Server is intended for mission-critical, heavy-load production systems as well as for embedding into mass-deployed software. MySQL is a registered trademark of MySQL AB.
The MySQL software is Dual Licensed. Users can choose to use the MySQL software as an Open Source/Free Software product under the terms of the GNU General Public License (http://www.fsf.org/licenses/) or can purchase a standard commercial license from MySQL AB. See section 1.4 MySQL Support and Licensing.
The MySQL Web site (http://www.mysql.com/) provides the latest information about the MySQL software.
The following list describes some sections of particular interest in this manual:
Important:
Reports of errors (often called ``bugs''), as well as questions and comments, should be sent to the general MySQL mailing list. See section 1.7.1.1 The MySQL Mailing Lists. See section 1.7.1.3 How to Report Bugs or Problems.
The mysqlbug
script should be used to generate bug reports on Unix.
(Windows distributions contain a file named `mysqlbug.txt' in the base
directory that can be used as a template for a bug report.)
For source distributions, the mysqlbug
script can be found in the
`scripts' directory. For binary distributions, mysqlbug
can be found in the `bin' directory (`/usr/bin' for the
MySQL-server
RPM package).
If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending an email message to security@mysql.com.
This is the Reference Manual for the MySQL Database System. It documents MySQL up to Version 5.0.0-alpha, but is also applicable for older versions of the MySQL software (such as 3.23 or 4.0-production) because functional changes are indicated with reference to a version number.
Because this manual serves as a reference, it does not provide general instruction on SQL or relational database concepts. It also will not teach you how to use your operating system or command line interpreter.
The MySQL Database Software is under constant development, and the Reference Manual is updated frequently as well. The most recent version of the manual is available online in searchable form at http://dev.mysql.com/doc/. Other formats also are available, including HTML, PDF, and Windows CHM 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
.
If you have any suggestions concerning additions or corrections to this manual, please send them to the documentation team at docs@mysql.com.
This manual was initially written by David Axmark and Michael ``Monty'' Widenius. It is now maintained by the MySQL Documentation Team, consisting of Arjen Lentz, Paul DuBois, and Stefan Hinz. For the many other contributors, see section B Credits.
The copyright (2004) to this manual is owned by the Swedish company MySQL AB. See section 1.4.2 Copyrights and Licenses Used by MySQL. MySQL and the MySQL logo are (registered) trademarks of MySQL AB. Other trademarks and registered trademarks referred to in this manual are the property of their respective owners, and are used for identification purposes only.
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 from within 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 statement that you execute from the
mysql
client program:
shell> type a shell command here mysql> type a mysql statement here
The ``shell'' is your command interpreter. On Unix, this is typically a
program such as sh
or csh
. On Windows, the equivalent program is
command.com
or cmd.exe
, typically run in a console window.
When you enter a command or statement shown in an example, do not type the prompt shown in the example.
Database, table, and column names must often be substituted into statements. 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 keywords are not case sensitive and may be written in uppercase or lowercase. This manual uses uppercase.
In syntax descriptions, square brackets (`[' and `]') are used
to indicate optional words or clauses. For example, in the following
statement, IF EXISTS
is optional:
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]
An ellipsis (...
) indicates the omission of a section of a statement,
typically to provide a shorter version of more complex syntax. For example,
INSERT ... SELECT
is shorthand for the form of INSERT
statement
that is followed by a SELECT
statement.
An ellipsis can also indicate that the preceding syntax element of a statement
may be repeated. In the following example, multiple reset_option
values
may be given, with each of those after the first preceded by commas:
RESET reset_option [,reset_option] ...
Commands for setting shell variables are shown using Bourne shell syntax. 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
If you are using csh
or tcsh
, you must issue commands somewhat
differently. You would execute the sequence just shown like this:
shell> setenv VARNAME value shell> some_command
MySQL, the most popular Open Source SQL database management system, is developed, distributed, and supported by MySQL AB. MySQL AB is a commercial company, founded by the MySQL developers, that builds its business by providing services around the MySQL database management system. See section 1.3 Overview of MySQL AB.
The MySQL Web site (http://www.mysql.com/) provides the latest information about MySQL software and MySQL AB.
The official way to pronounce ``MySQL'' is ``My Ess Que Ell'' (not ``my sequel''), but we don't mind if you pronounce it as ``my sequel'' or in some other localized way.
We 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 or
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
designed to allow third-party code that was written for use with mSQL
to
be ported easily for use with MySQL.
The derivation of the name MySQL is not clear. Our base directory and a large number of our libraries and tools have had the prefix ``my'' for well over 10 years. However, co-founder Monty Widenius's daughter is also named My. Which of the two gave its name to MySQL is still a mystery, even for us.
The name of the MySQL Dolphin (our logo) is ``Sakila,'' which was chosen by the founders of MySQL AB from a huge list of names suggested by users in our ``Name the Dolphin'' contest. The winning name was submitted by Ambrose Twebaze, an Open Source software developer from Swaziland, Africa. According to Ambrose, the name Sakila has its roots in SiSwati, the local language of Swaziland. Sakila is also the name of a town in Arusha, Tanzania, near Ambrose's country of origin, Uganda.
The following list describes some of the important characteristics of the MySQL Database Software. See also section 1.5 MySQL Development Roadmap for more information about current and upcoming features.
MyISAM
) with index compression.
FLOAT
, DOUBLE
, CHAR
, VARCHAR
,
TEXT
, BLOB
, DATE
, TIME
, DATETIME
,
TIMESTAMP
, YEAR
, SET
, ENUM
, and OpenGIS spatial
types.
See section 12 Column Types.
SELECT
and WHERE
clauses of queries. For example:
mysql> SELECT CONCAT(first_name, ' ', last_name) -> FROM citizen -> WHERE income/dependents > 10000 AND age > 30;
GROUP BY
and
ORDER BY
clauses. Support
for group functions (COUNT()
,
COUNT(DISTINCT ...)
,
AVG()
, STD()
,
SUM()
, MAX()
, MIN()
, and GROUP_CONCAT()
).
LEFT OUTER JOIN
and RIGHT OUTER JOIN
with both standard
SQL and ODBC syntax.
DELETE
, INSERT
, REPLACE
, and UPDATE
return
the number of rows that were changed (affected). It is possible to return
the number of rows matched instead by setting a flag when connecting to the
server.
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.
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 10.6 Treatment of Reserved Words in MySQL.
CHAR
, VARCHAR
,
BLOB
, or TEXT
column types.
latin1
(ISO-8859-1), german
, big5
, ujis
,
and more. For example,
the Scandinavian characters `â', `ä' and `ö' are
allowed in table and column names.
Unicode support is available as of MySQL 4.1.
mysqlcheck
client. MySQL also includes
myisamchk
, a very fast command-line utility for performing these
operations on MyISAM
tables.
See section 5 Database Administration.
--help
or -?
options to obtain online assistance.
This section addresses the questions, ``How stable is MySQL Server?'' and, ``Can I depend on MySQL Server in this project?'' We will try to clarify these issues and answer some important questions that concern many potential users. The information in this section is based on data gathered from the mailing lists, which are very active in identifying problems as well as reporting types of use.
The original code stems back to the early 1980s. It provides a stable code
base, and the ISAM
table format used by the original storage engine
remains backward-compatible.
At TcX, the predecessor of MySQL AB, MySQL code has worked
in projects since mid-1996, without any problems.
When the MySQL Database Software initially was released to a wider public,
our new users quickly found some pieces of untested code. Each new release
since then has had fewer portability problems, even though each new release
has also had many new features.
Each release of the MySQL Server has been usable. Problems have occurred only when users try code from the ``gray zones.'' Naturally, new users don't know what the gray zones are; this section therefore attempts to document those areas that are currently known. The descriptions mostly deal with Version 3.23 and 4.0 of MySQL Server. All known and reported bugs are fixed in the latest version, with the exception of those listed in the bugs section, which are design-related. See section 1.8.7 Known Errors and Design Deficiencies in MySQL.
The MySQL Server design is multi-layered with independent modules. Some of the newer modules are listed here with an indication of how well-tested each of them is:
InnoDB
tables (Stable)
InnoDB
transactional storage engine has been declared
stable in the MySQL 3.23 tree, starting from version 3.23.49.
InnoDB
is being used in large, heavy-load production systems.
BDB
tables (Gamma)
Berkeley DB
code is very stable, but we are still improving
the BDB
transactional storage engine interface in
MySQL Server, so it will take some time before this is as well
tested as the other table types.
Connector/ODBC
3.51 (Stable)
Connector/ODBC
3.51 uses ODBC SDK 3.51 and is in wide production use.
Some issues brought up appear to be application-related and independent of
the ODBC driver or underlying database server.
MyISAM
tables (Gamma)
MyISAM
storage engine
that checks when opening a table whether it was closed properly and executes
an automatic check or repair of the table if it wasn't.
MySQL 3.22 had a 4GB (4 gigabyte) limit on table size. With the
MyISAM
storage engine in MySQL 3.23, the maximum table
size was increased to 8 million terabytes (2 ^ 63 bytes). With this larger
allowed table size, the maximum effective table size for MySQL
databases now usually is determined by operating system constraints
on file sizes, not by MySQL internal limits.
The InnoDB
storage engine maintains InnoDB
tables within a
tablespace that can be created from several files. This allows a
table to exceed the maximum individual file size. The tablespace can include
raw disk partitions, which allows extremely large tables. The maximum
tablespace size is 64TB.
The following table lists some examples of operating system file-size limits:
Operating System | File-size Limit |
Linux-Intel 32-bit | 2GB, much more when using LFS |
Linux-Alpha | 8TB (?) |
Solaris 2.5.1 | 2GB (4GB possible with patch) |
Solaris 2.6 | 4GB (can be changed with flag) |
Solaris 2.7 Intel | 4GB |
Solaris 2.7 UltraSPARC | 512GB |
NetWare w/NSS filesystem | 8TB |
On Linux 2.2, you can get MyISAM
tables larger than 2GB in size by
using the Large File Support (LFS) patch for the ext2 filesystem. On Linux
2.4, patches also exist for ReiserFS to get support for big files. Most
current Linux distributions are based on kernel 2.4 and already include all
the required LFS patches. However, the maximum
available file size still depends on several factors, one of them being the
filesystem used to store MySQL tables.
For a detailed overview about LFS in Linux, have a look at Andreas Jaeger's Large File Support in Linux page at http://www.suse.de/~aj/linux_lfs.html.
By default, MySQL creates MyISAM
tables with an internal
structure that allows a maximum size of about 4GB. You can
check the maximum table size for a table with the SHOW TABLE STATUS
statement or with myisamchk -dv tbl_name
.
See section 14.5.3 SET
and SHOW
Syntax.
If you need a MyISAM
table that will be larger than 4GB in size (and your
operating system supports large files), the CREATE TABLE
statement
allows AVG_ROW_LENGTH
and MAX_ROWS
options.
See section 14.2.5 CREATE TABLE
Syntax.
You can also change these options with ALTER TABLE
after the table has
been created, to increase the table's maximum allowable size.
See section 14.2.2 ALTER TABLE
Syntax.
Other ways to work around file-size limits for MyISAM
tables are as
follows:
myisampack
to
compress it. myisampack
usually compresses a table by at
least 50%, so you can have, in effect, much bigger tables.
myisampack
also can merge multiple tables into a single table.
See section 8.2 myisampack
, the MySQL Compressed Read-only Table Generator.
MyISAM
data files is by using the RAID
options.
See section 14.2.5 CREATE TABLE
Syntax.
MERGE
library that allows
you to handle a collection of MyISAM
tables that have identical
structure as a single MERGE
table.
See section 15.2 The MERGE
Storage Engine.
The MySQL Server itself has no problems with Year 2000 (Y2K) compliance:
2037
for TIMESTAMP
values. For DATE
and DATETIME
values, dates through the year 9999
are accepted.
YEAR
column type
can store years 0
and 1901
to 2155
in one byte and
display them using two or four digits.
All two-digit years are considered to be in the range
1970
to 2069
, which means that if you store 01
in a
YEAR
column, MySQL Server treats it as 2001
.
The following simple demonstration illustrates that MySQL Server
has no problems with DATE
or DATETIME
values through the year
9999, and no problems with TIMESTAMP
values until after the year 2030:
mysql> DROP TABLE IF EXISTS y2k; Query OK, 0 rows affected (0.01 sec) mysql> CREATE TABLE y2k (date DATE, -> date_time DATETIME, -> time_stamp TIMESTAMP); Query OK, 0 rows affected (0.01 sec) mysql> INSERT INTO y2k VALUES -> ('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), -> ('2040-01-01','2040-01-01 00:00:00',20400101000000), -> ('9999-12-31','9999-12-31 23:59:59',99991231235959); Query OK, 14 rows affected (0.01 sec) Records: 14 Duplicates: 0 Warnings: 2 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 | | 2040-01-01 | 2040-01-01 00:00:00 | 00000000000000 | | 9999-12-31 | 9999-12-31 23:59:59 | 00000000000000 | +------------+---------------------+----------------+ 14 rows in set (0.00 sec)
The final two TIMESTAMP
column values are zero because the
year values (2040
, 9999
) exceed the TIMESTAMP
maximum. The
TIMESTAMP
data type, which is used to store the current time,
supports values that range from 19700101000000
to
20300101000000
on 32-bit machines (signed value). On 64-bit
machines, TIMESTAMP
handles values up to 2106
(unsigned
value).
Although MySQL Server itself is Y2K-safe, you may run into
problems if you use it with applications that are not Y2K-safe.
For example, many old applications store or manipulate years using
two-digit values (which are ambiguous) rather than four-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.
Thus, even though MySQL Server has no Y2K problems, it is the application's responsibility to provide unambiguous input. See section 12.3.4 Y2K Issues and Date Types for MySQL Server's rules for dealing with ambiguous date input data that contains two-digit year values.
MySQL AB is the company of the MySQL founders and main developers. MySQL AB was originally established in Sweden by David Axmark, Allan Larsson, and Michael ``Monty'' Widenius.
The developers of the MySQL server are all employed by the company. We are a virtual organization with people in a dozen countries around the world. We communicate extensively over the Internet every day with one another and with our users, supporters, and partners.
We are dedicated to developing the MySQL database software and promoting it to new users. MySQL AB owns the copyright to the MySQL source code, the MySQL logo and (registered) trademark, and this manual. See section 1.2 Overview of the MySQL Database Management System.
The MySQL core values show our dedication to MySQL and Open Source.
These core values direct how MySQL AB works with the MySQL server software:
These are the core values of the company MySQL AB and its employees:
The MySQL Web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.
By the way, the ``AB'' part of the company name is the acronym for the Swedish ``aktiebolag,'' or ``stock company.'' It translates to ``MySQL, Inc.'' In fact, MySQL, Inc. and MySQL GmbH are examples of MySQL AB subsidiaries. They are located in the US and Germany, respectively.
One of the most common questions we encounter is, ``How can you make a living from something you give away for free?'' This is how:
The company has been profitable since its inception. In October 2001, we accepted venture financing from leading Scandinavian investors and a handful of business angels. This investment is used to solidify our business model and build a basis for sustainable growth.
MySQL AB is run and owned by the founders and main developers of the MySQL database. The developers are committed to providing support to customers and other users in order to stay in touch with their needs and problems. All our support is provided by qualified developers. Really tricky questions are answered by Michael ``Monty'' Widenius, principal author of the MySQL Server.
Paying customers receive high-quality support directly from MySQL AB. MySQL AB also provides the MySQL mailing lists as a community resource where anyone may ask questions.
For more information and ordering support at various levels, see section 1.4 MySQL Support and Licensing.
MySQL AB delivers MySQL and related training worldwide. We offer both open courses and in-house courses tailored to the specific needs of your company. MySQL Training is also available through our partners, the Authorized MySQL Training Centers.
Our training material uses the same sample databases used in our documentation and our sample applications, and is always updated to reflect the latest MySQL version. Our trainers are backed by the development team to guarantee the quality of the training and the continuous development of the course material. This also ensures that no questions raised during the courses remain unanswered.
Attending our training courses will enable you to achieve your MySQL application goals. You will also:
If you are interested in our training as a potential participant or as a training partner, please visit the training section at http://www.mysql.com/training/, or send email to training@mysql.com.
For details about the MySQL Certification Program, please see http://www.mysql.com/certification/.
MySQL AB and its Authorized Partners offer consulting services to users of MySQL Server and to those who embed MySQL Server in their own software, all over the world.
Our consultants can help you design and tune your databases, construct efficient queries, tune your platform for optimal performance, resolve migration issues, set up replication, build robust transactional applications, and more. We also help customers embed MySQL Server in their products and applications for large-scale deployment.
Our consultants work in close collaboration with our development team, which ensures the technical quality of our professional services. Consulting assignments range from two-day power-start sessions to projects that span weeks and months. Our expertise covers not only MySQL Server, it also extends into programming and scripting languages such as PHP, Perl, and more.
If you are interested in our consulting services or want to become a consulting partner, please visit the consulting section of our Web site at http://www.mysql.com/consulting/ or contact our consulting staff at consulting@mysql.com.
The MySQL database is released under the GNU General Public License (GPL). This means that the MySQL software can be used free of charge under the GPL. If you do not want to be bound by the GPL terms (such as the requirement that your application must also be GPL), you may purchase a commercial license for the same product from MySQL AB; see https://order.mysql.com/. Since MySQL AB owns the copyright to the MySQL source code, we are able to employ Dual Licensing, which means that the same product is available under GPL and under a commercial license. This does not in any way affect the Open Source commitment of MySQL AB. For details about when a commercial license is required, please see section 1.4.3 MySQL Licenses.
We also sell commercial licenses of third-party Open Source GPL
software that adds value to MySQL Server. A good example is the
InnoDB
transactional storage engine that offers ACID
support, row-level locking, crash recovery, multi-versioning, foreign
key support, and more. See section 16 The InnoDB
Storage Engine.
MySQL AB has a worldwide partner program that covers training courses, consulting and support, publications, plus reselling and distributing MySQL and related products. MySQL AB Partners get visibility on the http://www.mysql.com/ Web site and the right to use special versions of the MySQL (registered) trademarks to identify their products and promote their business.
If you are interested in becoming a MySQL AB Partner, please email partner@mysql.com.
The word MySQL and the MySQL dolphin logo are (registered) trademarks of MySQL AB. See section 1.4.4 MySQL AB Logos and Trademarks. These trademarks represent a significant value that the MySQL founders have built over the years.
The MySQL Web site (http://www.mysql.com/) is popular among developers and users. In December 2003, we served 16 million page views. Our visitors represent a group that makes purchase decisions and recommendations for both software and hardware. Twelve percent of our visitors authorize purchase decisions, and only nine percent have no involvement at all in purchase decisions. More than 65% have made one or more online business purchases within the last half-year, and 70% plan to make one in the next few months.
The MySQL Web site (http://www.mysql.com/) provides the latest information about MySQL and MySQL AB.
For press services and inquiries not covered in our news releases (http://www.mysql.com/news-and-events/), please send email to press@mysql.com.
If you have a support contract with MySQL AB, you will get timely, precise answers to your technical questions about the MySQL software. For more information, see section 1.4.1 Support Offered by MySQL AB. On our Web site, see http://www.mysql.com/support/, or send email to sales@mysql.com.
For information about MySQL training, please visit the training section at http://www.mysql.com/training/, or send email to training@mysql.com. See section 1.3.1.2 Training and Certification.
For information on the MySQL Certification Program, please see http://www.mysql.com/certification/. See section 1.3.1.2 Training and Certification.
If you're interested in consulting, please visit the consulting section of our Web site at http://www.mysql.com/consulting/, or send email to consulting@mysql.com. See section 1.3.1.3 Consulting.
Commercial licenses may be purchased online at https://order.mysql.com/. There you will also find information on how to fax your purchase order to MySQL AB. More information about licensing can be found at http://www.mysql.com/products/licensing/. If you have questions regarding licensing or you want a quote for high-volume licensing, please fill in the contact form on our Web site (http://www.mysql.com/), or send email to licensing@mysql.com (for licensing questions) or to sales@mysql.com (for sales inquiries). See section 1.4.3 MySQL Licenses.
If you represent a business that is interested in partnering with MySQL AB, please send email to partner@mysql.com. See section 1.3.1.5 Partnering.
For more information on the MySQL trademark policy, refer to http://www.mysql.com/company/trademark.html, or send email to trademark@mysql.com. See section 1.4.4 MySQL AB Logos and Trademarks.
If you are interested in any of the MySQL AB jobs listed in our jobs section (http://www.mysql.com/company/jobs/), please send email to jobs@mysql.com. Please do not send your CV as an attachment, but rather as plain text at the end of your email message.
For general discussion among our many users, please direct your attention to the appropriate mailing list. See section 1.7.1 MySQL Mailing Lists.
Reports of errors (often called ``bugs''), as well as questions and comments, should be sent to the general MySQL mailing list. See section 1.7.1.1 The MySQL Mailing Lists. If you have found a sensitive security bug in MySQL Server, please let us know immediately by sending email to security@mysql.com. See section 1.7.1.3 How to Report Bugs or Problems.
If you have benchmark results that we can publish, please contact us via email at benchmarks@mysql.com.
If you have suggestions concerning additions or corrections to this manual, please send them to the documentation team via email at docs@mysql.com.
For questions or comments about the workings or content of the MySQL Web site (http://www.mysql.com/), please send email to webmaster@mysql.com.
MySQL AB has a privacy policy, which can be read at http://www.mysql.com/company/privacy.html. For any queries regarding this policy, please send email to privacy@mysql.com.
For all other inquiries, please send email to info@mysql.com.
This section describes MySQL support and licensing arrangements.
Technical support from MySQL AB means individualized answers to your unique problems direct from the software engineers who code the MySQL database engine.
We try to take a broad and inclusive view of technical support. Almost any problem involving MySQL software is important to us if it's important to you. Typically customers seek help on how to get different commands and utilities to work, remove performance bottlenecks, restore crashed systems, understand the impact of operating system or networking issues on MySQL, set up best practices for backup and recovery, utilize APIs, and so on. Our support covers only the MySQL server and our own utilities, not third-party products that access the MySQL server, although we try to help with these where we can.
Detailed information about our various support options is given at http://www.mysql.com/support/, where support contracts can also be ordered online. To contact our sales staff, send email to sales@mysql.com.
Technical support is like life insurance. You can live happily without it for years. However, when your hour arrives, it becomes critically important, but it's too late to buy it. If you use MySQL Server for important applications and encounter sudden difficulties, it may be too time-consuming to figure out all the answers yourself. You may need immediate access to the most experienced MySQL troubleshooters available, those employed by MySQL AB.
MySQL AB owns the copyright to the MySQL source code, the MySQL logos and (registered) trademarks, and this manual. See section 1.3 Overview of MySQL AB. Several different licenses are relevant to the MySQL distribution:
mysqlclient
library and the client, as well as the GNU readline
library,
are covered by the GNU General Public License.
See section G GNU General Public License.
The text of this license can be found as the file `COPYING'
in MySQL distributions.
getopt
library is covered by the
GNU Lesser General Public License.
See http://www.fsf.org/licenses/.
regexp
library) are covered
by a Berkeley-style copyright.
For information about how the MySQL licenses work in practice, please refer to section 1.4.3 MySQL Licenses and section 1.4.4 MySQL AB Logos and Trademarks.
The MySQL software is released under the GNU General Public License (GPL), which is probably the best known Open Source license. The formal terms of the GPL license can be found at http://www.fsf.org/licenses/. See also http://www.fsf.org/licenses/gpl-faq.html and http://www.gnu.org/philosophy/enforcing-gpl.html.
Our GPL licensing is supported by an optional license exception that enables many Free/Libre and Open Source Software (``FLOSS'') applications to include the GPL-licensed MySQL client libraries despite the fact that not all FLOSS licenses are compatible with the GPL. For details, see http://www.mysql.com/products/licensing/foss-exception.html.
Because the MySQL software is released under the GPL, it may often be used for free, but for certain uses you may want or need to buy commercial licenses from MySQL AB at https://order.mysql.com/. See http://www.mysql.com/products/licensing/ for more information.
Older versions of MySQL (3.22 and earlier) are subject to a stricter license (http://www.mysql.com/products/licensing/mypl.html). See the documentation of the specific version for information.
Please note that the use of the MySQL software under commercial license, GPL, or the old MySQL license does not automatically give you the right to use MySQL AB (registered) trademarks. See section 1.4.4 MySQL AB Logos and Trademarks.
The GPL license is contagious in the sense that when a program is linked to a GPL program, all the source code for all the parts of the resulting product must also be released under the GPL. If you do not follow this GPL requirement, you break the license terms and forfeit your right to use the GPL program altogether. You also risk damages.
You need a commercial license under these conditions:
Our GPL licensing is supported by an optional license exception that enables many Free/Libre and Open Source Software (``FLOSS'') applications to include the GPL-licensed MySQL client libraries despite the fact that not all FLOSS licenses are compatible with the GPL. For details, see http://www.mysql.com/products/licensing/foss-exception.html.
If you require a commercial license, you will need one for each installation of the MySQL software. This covers any number of CPUs on a machine, and there is no artificial limit on the number of clients that connect to the server in any way.
For commercial licenses, please visit our Web site at http://www.mysql.com/products/licensing/. For support contracts, see http://www.mysql.com/support/. If you have special needs, please contact our sales staff via email at sales@mysql.com.
You can use the MySQL software for free under the GPL if you adhere to the conditions of the GPL. For additional details about the GPL, including answers to common questions, see the generic FAQ from the Free Software Foundation at http://www.fsf.org/licenses/gpl-faq.html.
Our GPL licensing is supported by an optional license exception that enables many Free/Libre and Open Source Software (``FLOSS'') applications to include the GPL-licensed MySQL client libraries despite the fact that not all FLOSS licenses are compatible with the GPL. For details, see http://www.mysql.com/products/licensing/foss-exception.html.
Common uses of the GPL include:
If your use of MySQL database software does not require a commercial license, we encourage you to purchase support from MySQL AB anyway. This way you contribute toward MySQL development and also gain immediate advantages for yourself. See section 1.4.1 Support Offered by MySQL AB.
If you use the MySQL database software in a commercial context such that you profit by its use, we ask that you further the development of the MySQL software by purchasing some level of support. We feel that if the MySQL database helps your business, it is reasonable to ask that you help MySQL AB. (Otherwise, if you ask us support questions, you are not only using for free something into which we've put a lot a work, you're asking us to provide free support, too.)
Many users of the MySQL database want to display the MySQL AB dolphin logo on their Web sites, books, or boxed products. We welcome and encourage this, although it should be noted that the word MySQL and the MySQL dolphin logo are (registered) trademarks of MySQL AB and may only be used as stated in our trademark policy at http://www.mysql.com/company/trademark.html.
The MySQL dolphin logo was designed by the Finnish advertising agency Priority in 2001. The dolphin was chosen as a suitable symbol for the MySQL database management system, which is like a smart, fast, and lean animal, effortlessly navigating oceans of data. We also happen to like dolphins.
The original MySQL logo may only be used by representatives of MySQL AB and by those having a written agreement allowing them to do so.
We have designed a set of special Conditional Use logos that may be downloaded from our Web site at http://www.mysql.com/press/logos.html and used on third-party Web sites without written permission from MySQL AB. The use of these logos is not entirely unrestricted but, as the name implies, subject to our trademark policy that is also available on our Web site. You should read through the trademark policy if you plan to use them. The requirements are basically as follows:
Contact us via email at trademark@mysql.com to inquire about special arrangements to fit your needs.
You need written permission from MySQL AB before using MySQL logos in the following cases:
Due to legal and commercial reasons, we monitor the use of MySQL (registered) trademarks on products, books, and other items. We usually require a fee for displaying MySQL AB logos on commercial products, since we think it is reasonable that some of the revenue is returned to fund further development of the MySQL database.
MySQL partnership logos may be used only by companies and persons having a written partnership agreement with MySQL AB. Partnerships include certification as a MySQL trainer or consultant. For more information, please see section 1.3.1.5 Partnering.
MySQL AB welcomes references to the MySQL database, but it should be
noted that the word MySQL is a registered trademark of MySQL AB.
Because of this, you must append the ``registered trademark'' notice
symbol (R
) to
the first or most prominent use of the word MySQL in a text and,
where appropriate, state that MySQL is a registered trademark of
MySQL AB. For more information, please refer to our trademark policy at
http://www.mysql.com/company/trademark.html.
Use of the word MySQL in company or product names or in Internet domain names is not allowed without written permission from MySQL AB.
This section provides a snapshot of the MySQL development roadmap, including major features implemented or planned for MySQL 4.0, 4.1, 5.0, and 5.1. The following sections provide information for each release series.
The production release series is MySQL 4.0, which was declared stable for production use as of Version 4.0.12, released in March 2003. This means that future 4.0 development will be limited only to making bugfixes. For the older MySQL 3.23 series, only critical bugfixes will be made.
Active MySQL development currently is taking place in the MySQL 4.1 and 5.0 release series. This means that new features are being added to MySQL 4.1 and MySQL 5.0. Both 4.1 and 5.0 are available now in alpha status.
Before upgrading from one release series to the next, please see the notes at section 2.5 Upgrading/Downgrading MySQL.
Plans for some of the most requested features are summarized in the following table.
Feature | MySQL Series |
Unions | 4.0 |
Subqueries | 4.1 |
R-trees | 4.1 (for MyISAM tables)
|
Stored procedures | 5.0 |
Views | 5.0 |
Cursors | 5.0 |
Foreign keys | 5.1 (already implemented in 3.23 for InnoDB )
|
Triggers | 5.1 |
Full outer join | 5.1 |
Constraints | 5.1 |
Long awaited by our users, MySQL Server 4.0 is now available in production status.
MySQL 4.0 is available for download at http://dev.mysql.com/ and from our mirrors. MySQL 4.0 has been tested by a large number of users and is in production use at many large sites.
The major new features of MySQL Server 4.0 are geared toward our existing business and community users, enhancing the MySQL database software as the solution for mission-critical, heavy-load database systems. Other new features target the users of embedded databases.
INSERT
statements, searching on
packed indexes, full-text searching (using FULLTEXT
indexes), and
COUNT(DISTINCT)
.
InnoDB
storage engine as standard
InnoDB
storage engine is now offered as a standard feature of the
MySQL server. This means full support for ACID transactions, foreign
keys with cascading UPDATE
and DELETE
, and row-level locking
are now standard features.
See section 16 The InnoDB
Storage Engine.
FULLTEXT
search properties of MySQL Server 4.0 enables
FULLTEXT
indexing of large text masses with both binary
and natural-language searching logic. You can customize minimal word
length and define your own stop word lists in any human language,
enabling a new set of applications to be built with MySQL Server.
See section 13.6 Full-Text Search Functions.
UNION
statement, a long-awaited standard SQL feature.
TRUNCATE TABLE
(as in Oracle).
latin1_de
, which ensures that the
German sorting order sorts words with umlauts in the same order
as do German telephone books.
mysqld
parameters (startup options) can now be set without taking
down the server. This is a convenient feature for database administrators
(DBAs).
See section 14.5.3.1 SET
Syntax.
DELETE
and UPDATE
statements have been added.
MyISAM
storage engine now supports symbolic
linking at the table level (and not just the database level as before).
SQL_CALC_FOUND_ROWS
and FOUND_ROWS()
are new functions that make it
possible to find out the number of rows a SELECT
query that includes a
LIMIT
clause would have returned without that clause.
The news section of this manual includes a more in-depth list of features. See section C.3 Changes in release 4.0.x (Production).
The libmysqld
embedded server library makes MySQL Server suitable for
a vastly expanded realm of applications. By using this library, developers can
embed MySQL Server into various applications and electronics devices, where
the end user has no knowledge of there actually being an underlying
database. Embedded MySQL Server is ideal for use behind
the scenes in Internet appliances, public kiosks, turnkey
hardware/software combination units, high performance Internet
servers, self-contained databases distributed on CD-ROM, and so on.
Many users of libmysqld
will benefit from the MySQL
Dual Licensing. For those not wishing to be bound by the GPL,
the software is also made available under a commercial license.
The embedded MySQL library uses the same interface as the normal
client library, so it is convenient and easy to use.
See section 21.2.15 libmysqld, the Embedded MySQL Server Library.
On windows there are two different libraries:
libmysqld.lib | Dynamic library for threadded applications. |
mysqldemb.lib | Static library for not threaded applications. |
MySQL Server 4.0 laid the foundation for new features implemented in MySQL 4.1, such as subqueries and Unicode support, and for the work on stored procedures being done in version 5.0. These features come at the top of the wish list of many of our customers.
With these additions, critics of the MySQL Database Server have to be more imaginative than ever in pointing out deficiencies in the MySQL database management system. Already well-known for its stability, speed, and ease of use, MySQL Server is able to fulfill the requirement checklists of very demanding buyers.
The MySQL 4.1 features listed in this section already are implemented. A few other MySQL 4.1 features are still planned; see section 1.6.1 New Features Planned for 4.1.
Most new features being coded are or will be available in MySQL 5.0. See section 1.6.2 New Features Planned for 5.0.
SELECT
statement nested within another statement.
A ``derived table'' (an unnamed view) is a subquery in the FROM
clause
of another statement.
See section 14.1.8 Subquery Syntax.
BTREE
indexing is now supported for HEAP
tables,
significantly improving response time for non-exact searches.
CREATE TABLE tbl_name2 LIKE tbl_name1
allows you to create, with
a single statement, a new table with a structure exactly like that of an
existing table.
MyISAM
storage engine now supports
OpenGIS spatial types for storing geographical data.
See section 19 Spatial Extensions in MySQL.
SHOW WARNINGS
shows warnings for the last command.
See section 14.5.3.20 SHOW WARNINGS
Syntax.
utf8
and ucs2
character sets.
HELP
command that can be used
to get help information for SQL statements.
The advantage of having this information on the server side is that the
information is always applicable to the particular server version that you
actually are using.
Because this information is available by issuing an SQL statement, any client
can be written to access it.
For example, the help
command of the mysql
command-line client
has been modified to have this capability.
INSERT ... ON DUPLICATE KEY UPDATE ...
syntax has been
implemented. This allows you to UPDATE
an existing row if the
INSERT
would have caused a duplicate in a PRIMARY
or
UNIQUE
index.
See section 14.1.4 INSERT
Syntax.
GROUP_CONCAT()
adds the extremely useful capability of concatenating column values from
grouped rows into a single result string.
See section 13.9 Functions and Modifiers for Use with GROUP BY
Clauses.
The news section of this manual includes a more in-depth list of features. See section C.2 Changes in release 4.1.x (Alpha).
New features are being added to MySQL 4.1. The alpha version is already available for download. See section 1.5.2.3 Ready for Immediate Development Use.
The set of features being added to version 4.1 is mostly fixed. Additional development is already ongoing for version 5.0. MySQL 4.1 is going through the steps of Alpha (during which time new features might still be added/changed), Beta (when we have feature freeze and only bug corrections will be done), and Gamma (indicating that a production release is just weeks ahead). At the end of this process, MySQL 4.1 will become the new production release.
MySQL 4.1 is currently in the alpha stage, and binaries are available for download at http://dev.mysql.com/downloads/mysql/4.1.html. All binary releases pass our extensive test suite without any errors on the platforms on which we test. See section C.2 Changes in release 4.1.x (Alpha).
For those wishing to use the most recent development source for MySQL 4.1, we make our 4.1 BitKeeper repository publicly available. See section 2.3.3 Installing from the Development Source Tree.
New development for MySQL is focused on the 5.0 release, featuring stored procedures and other new features. See section 1.6.2 New Features Planned for 5.0.
For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See section 2.3.3 Installing from the Development Source Tree. As of December 2003, binary builds of version 5.0 are also available.
This section summarizes the features that we plan to implement in MySQL Server. The items are ordered by release series. Within a list, items are shown in approximately the order they will be done.
Note: If you are an enterprise-level user with an urgent need for a particular feature, please contact sales@mysql.com to discuss sponsoring options. Targeted financing by sponsor companies allows us to allocate additional resources for specific purposes. One example of a feature sponsored in the past is replication.
The following features are not yet implemented in MySQL 4.1, but are planned for implementation as MySQL 4.1 moves into its beta phase. For a list what is already done in MySQL 4.1, see section 1.5.2.1 Features Available in MySQL 4.1.
The following features are planned for inclusion into MySQL 5.0. Some of the features such as stored procedures are complete and are included in MySQL 5.0 alpha, which is available now. Others such as cursors are only partially available. Expect these and other features to mature and be fully supported in upcoming releases.
Note that because we have many developers that are working on different projects, there will also be many additional features. There is also a small chance that some of these features will be added to MySQL 4.1. For a list what is already done in MySQL 4.1, see section 1.5.2.1 Features Available in MySQL 4.1.
For those wishing to take a look at the bleeding edge of MySQL development, we make our BitKeeper repository for MySQL version 5.0 publicly available. See section 2.3.3 Installing from the Development Source Tree. As of December 2003, binary builds of version 5.0 are also available.
MyISAM
tables that an index
should be created as an RTREE
index. (In MySQL 4.1, RTREE
indexes
are used internally for geometrical data that use GIS data types, but cannot be
created on request.)
MEMORY
tables.
VARCHAR
support (column lengths longer than 255, and
no stripping of trailing whitespace).
There is already support for this in the MyISAM
storage engine,
but it is not yet available at the user level.
SHOW COLUMNS FROM tbl_name
(used by the mysql
client to allow
expansions of column names) should not open the table, only the
definition file. This will require less memory and be much faster.
DELETE
on MyISAM
tables to use the record cache.
To do this, we need to update the threads record cache when we update
the `.MYD' file.
MEMORY
tables:
RENAME TABLE
on a table used in an active
MERGE
table possibly corrupting the table.
The news section of this manual includes a more in-depth list of features. See section C.1 Changes in release 5.0.x (Development).
FOREIGN KEY
support for all table types, not just InnoDB
.
BIT
type to take one bit. (BIT
now takes one byte;
it is treated as a synonym for TINYINT
.)
RENAME DATABASE
. To make this safe for all storage engines,
it should work as follows:
RENAME
command.
CONNECT BY PRIOR
to search tree-like (hierarchical)
structures.
SUM(DISTINCT)
.
INSERT SQL_CONCURRENT
and mysqld --concurrent-insert
to do
a concurrent insert at the end of a table if the table is read-locked.
UPDATE
statements. For example:
UPDATE foo SET @a:=a+b,a=@a, b=@a+c
.
GROUP BY
, as in the following statement:
SELECT id, @a:=COUNT(*), SUM(sum_col)/@a FROM tbl_name GROUP BY id
.
IMAGE
option to LOAD DATA INFILE
to not update
TIMESTAMP
and AUTO_INCREMENT
columns.
LOAD DATA INFILE ... UPDATE
syntax that works like this:
LOAD DATA INFILE ... REPLACE INTO
.
LOAD DATA INFILE
understand syntax like this:
LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name TEXT_FIELDS (text_col1, text_col2, text_col3) SET table_col1=CONCAT(text_col1, text_col2), table_col3=23 IGNORE text_col3This can be used to skip over extra columns in the text file, or update columns based on expressions of the read data.
SET
type columns:
ADD_TO_SET(value,set)
REMOVE_FROM_SET(value,set)
mysql
in the middle of a query, you should open
another connection and kill the old running query.
Alternatively, an attempt should be made to detect this in the server.
SHOW INFO FROM tbl_name
for basic table information
should be implemented.
SELECT a FROM tbl_name1 LEFT JOIN tbl_name2 USING (a)
; in this
case a
is assumed to come from tbl_name1
.
DELETE
and REPLACE
options to the UPDATE
statement
(this will delete rows when a duplicate-key error occurs while updating).
DATETIME
to store fractions of seconds.
regexp
library instead of the current
one (the new library should be much faster than the current one).
DEFAULT
values to columns. Produce an error for
any INSERT
statement that is missing a value for a column that has no
DEFAULT
.
ANY()
, EVERY()
, and SOME()
group functions. In
standard SQL, these work only on boolean columns, but we can extend these to
work on any columns or expressions by treating a value of zero as FALSE and
non-zero values as TRUE.
MAX(column)
to be the same as the column type:
mysql> CREATE TABLE t1 (a DATE); mysql> INSERT INTO t1 VALUES (NOW()); mysql> CREATE TABLE t2 SELECT MAX(a) FROM t1; mysql> SHOW COLUMNS FROM t2;
MyISAM
recovery at the same time.
INSERT INTO ... SELECT
to optionally use concurrent inserts.
SELECT MIN(column) ... GROUP BY
.
long_query_time
with a granularity
in microseconds.
myisampack
code into the server so that it can perform
PACK
or COMPRESS
operations.
INSERT/DELETE/UPDATE
so that we
can gracefully recover if the index file gets full.
ALTER TABLE
on a table that is symlinked to another
disk, create temporary tables on that disk.
DATE/DATETIME
type that handles time zone information
properly, to make dealing with dates in different time zones easier.
configure
so that all libraries (like MyISAM
)
can be compiled without threads.
LIMIT
arguments; for example,
LIMIT @a,@b
.
mysql
to a Web browser.
LOCK DATABASES
(with various options).
SHOW STATUS
. Record reads and
updates. Selects on a single table and selects with joins. Mean number of
tables in selects. Number of ORDER BY
and GROUP BY
queries.
mysqladmin copy database new-database
; this requires a COPY
operation to be added to mysqld
.
SHOW HOSTS
for printing information about the hostname cache.
NULL
for calculated columns.
Item_copy_string
on numerical values to avoid
number-to-string-to-number conversion in case of
SELECT COUNT(*)*(id+0) FROM tbl_name GROUP BY id
.
ALTER TABLE
doesn't abort clients
that execute INSERT DELAYED
.
UPDATE
clause,
they contain the old values from before the update started.
get_changed_tables(timeout,table1,table2,...)
.
mmap()
when possible. Now only
compressed tables use mmap()
.
SET TIMESTAMP=val;
.
col_name=n
is found in an expression, for some constant n
, replace other
occurrences of col_name
within the expression with n
.
Currently, this is done only for some simple cases.
key
= expr
comparisons. At the moment, only
key
= column
or key
= constant
comparisons are
optimized.
MINUS
, INTERSECT
, and FULL OUTER JOIN
.
(Currently UNION
and LEFT|RIGHT OUTER JOIN
are supported.)
SQL_OPTION MAX_SELECT_TIME=val
, for placing a time limit on a query.
LIMIT
to allow retrieval of data from the end of a result set.
mysqld_safe
: According to FSSTND (which
Debian tries to follow), PID files should go into `/var/run/<progname>.pid'
and log files into `/var/log'. It would be nice if you could put the
"DATADIR" in the first declaration of "pidfile" and "log" so that the
placement of these files can be changed with a single statement.
LOAD DATA INFILE
statement
to read files that have been compressed with gzip
.
BLOB
columns (partly solved now).
JOIN
with parentheses.
GET_LOCK()
to obtain more than one lock. When doing this, it is
also necessary to handle the possible deadlocks this change will introduce.
We aim toward full compliance with ANSI/ISO SQL. There are no features we plan not to implement.
This section introduces the MySQL mailing lists and provides guidelines as to how the lists should be used. When you subscribe to a mailing list, you will receive all postings to the list as email messages. You can also send your own questions and answers to the list.
To subscribe to or unsubscribe from any of the mailing lists described in this section, visit http://lists.mysql.com/. Please do not send messages about subscribing or unsubscribing to any of the mailing lists, because such messages are distributed automatically to thousands of other users.
Your local site may have many subscribers to a MySQL mailing list.
If so, the site 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.
If you wish to have traffic for a mailing list go to a separate mailbox in
your mail program, set up a filter based on the message headers. You can
use either the List-ID:
or Delivered-To:
headers to identify
list messages.
The MySQL mailing lists are as follows:
announce
mysql
mysql-digest
mysql
list in digest form. Subscribing to this list means
you will get all list messages, sent as one large mail message once a day.
bugs
bugs-digest
bugs
list in digest form.
internals
internals-digest
internals
list in digest form.
mysqldoc
mysqldoc-digest
mysqldoc
list in digest form.
benchmarks
benchmarks-digest
benchmarks
list in digest form.
packagers
packagers-digest
packagers
list in digest form.
java
java-digest
java
list in digest form.
win32
win32-digest
win32
list in digest form.
myodbc
myodbc-digest
myodbc
list in digest form.
gui-tools
MySQL
Administrator
and the MySQL Control Center
graphical client.
gui-tools-digest
gui-tools
list in digest form.
cluster
cluster-digest
cluster
list in digest form.
plusplus
plusplus-digest
plusplus
list in digest form.
msql-mysql-modules
msql-mysql-modules
, which is now named DBD::mysql
.
msql-mysql-modules-digest
msql-mysql-modules
list in digest form.
If you're unable to get an answer to your questions from a MySQL mailing list, one option is to purchase support from MySQL AB. This will put you in direct contact with MySQL developers. See section 1.4.1 Support Offered by MySQL AB.
The following table shows some MySQL mailing lists in languages other than English. These lists are not operated by MySQL AB.
mysql-france-subscribe@yahoogroups.com
list@tinc.net
subscribe mysql your@email.address
to this list.
mysql-de-request@lists.4t2.com
subscribe mysql-de your@email.address
to this list.
You can find information about this mailing list at
http://www.4t2.com/mysql/.
mysql-br-request@listas.linkway.com.br
subscribe mysql-br your@email.address
to this list.
mysql-alta@elistas.net
subscribe mysql your@email.address
to this list.
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, please follow the guidelines on sending mail to a MySQL mailing list, outlined in the next section, before contacting us.
The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log in to the system, you will also be able to enter new reports.
Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug 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). mysqlbug
can be
found in the `scripts' directory (source distribution) and in the
`bin' directory under your MySQL installation directory (binary distribution).
If you are unable to use mysqlbug
(for example, if you are running
on Windows), it is still vital that you include all the necessary information
noted in this section (most importantly, a description of the operating system
and the MySQL version).
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.
Preferably, you should test the problem using the latest production or
development version of MySQL Server before posting. Anyone should be
able to repeat the bug by just using mysql test < script_file
on the
included test case or by running the shell or Perl script that is included in the
bug report.
All bugs posted in the bugs database at http://bugs.mysql.com/ will be corrected or documented in the next MySQL release. If only minor code changes are needed to correct a problem, we may also post a patch that fixes the problem.
If you have found a sensitive security bug in MySQL, you can send email to security@mysql.com.
If you have a repeatable bug report, please report it to the bugs
database at http://bugs.mysql.com/. Note that even in this case
it's good to run the mysqlbug
script first to find information
about your system. Any bug that we are able to repeat has a high chance
of being fixed in the next MySQL release.
To report other problems, you can use one of the MySQL mailing lists.
Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is this: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.
The most common errors made in bug reports are (a) not including the version number of the MySQL distribution used, and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and 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 already been fixed in newer MySQL versions. Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.
If you compiled MySQL from source, 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 your problem depends on your compiler, we need to know what compiler you use. Note that every compiling problem should be regarded as a bug and reported accordingly.
It is most helpful when a good description of the problem is included in the bug report. That is, give a good example of everything you did that led to the problem and describe, in exact detail, the problem itself. The best reports are those that include a full example showing how to reproduce the bug or problem. See section D.1.6 Making a Test Case If You Experience Table Corruption.
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 lettercase should be observed.) You should never try to reproduce from memory what the error message was; instead, copy and paste the entire message into your report.
If you have a problem with Connector/ODBC (MyODBC), please try to generate a MyODBC trace file and send it with your report. See section 21.3.7 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 later in this section).
Please include the following information in your report:
mysqladmin version
. The mysqladmin
program can be found in the `bin' directory under your MySQL
installation directory.
uname -a
.
mysqld
died, you should also report the query that crashed
mysqld
. You can usually find this out by running mysqld
with
query logging enabled, and then looking in the log after mysqld
crashes
See section D.1.5 Using Log Files to Find Cause of Errors in mysqld
.
mysqldump --no-data db_name tbl_name
. This is very easy
to do and is a powerful way to get information about any table in a database.
The information 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. You
should also include the output from SHOW CREATE TABLE tbl_name
for each involved table. The more information you give about your
situation, the more likely it is that someone can help you.
The following is an example of a very good bug report. It should be posted
with the mysqlbug
script. The example uses 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>
mysqld
, try to provide an
input script that will reproduce the anomaly. This script should include any
necessary source files. The more closely the script can reproduce your
situation, the better. If you can make a reproducible test case, you should
post it on http://bugs.mysql.com/ for high-priority treatment.
If you can't provide a script, you should at least include the output
from mysqladmin variables extended-status processlist
in your mail to
provide some information on how your system is performing.
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://ftp.mysql.com/pub/mysql/upload/. Then enter
the problem into our bugs database at http://bugs.mysql.com/.
mysqld
server as well as the options that you use to run any MySQL client programs.
The options to programs such as 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. If you use any modules, such
as Perl or PHP, please include the version numbers of those as well.
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 Server doesn't support the syntax you are
using. If you are using the current version and the manual at
http://dev.mysql.com/doc/ doesn't cover the
syntax you are using, MySQL Server doesn't support your query. In this
case, your only options are to implement the syntax yourself or email
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 Server, you should check the MySQL change history to see
when the syntax was implemented. In this case, you have the option of
upgrading to a newer version of MySQL Server. See section C MySQL Change History.
CHECK TABLE
and REPAIR TABLE
or with myisamchk
.
See section 5 Database Administration.
If you are running Windows, please verify that lower_case_table_names
is 1 or 2 with SHOW VARIABLES LIKE 'lower_case_table_names'
.
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 A.1 How to Determine What Is Causing a Problem.
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 whether someone else has experienced (and perhaps solved) the problem.
For information on reporting bugs in MyODBC
, see section 21.3.4 How to Report Problems with MyODBC.
For solutions to some common problems, see section A 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.
In addition to the various MySQL mailing lists, you can find experienced
community people on IRC
(Internet Relay Chat
).
These are the best networks/channels currently known to us:
#mysql
Primarily MySQL questions, but other database and general SQL questions are welcome.
Questions about PHP, Perl or C in combination with MySQL are also common.
#mysql
MySQL questions.
If you are looking for IRC client software to connect to an IRC network,
take a look at X-Chat
(http://www.xchat.org/).
X-Chat (GPL licensed) is available for Unix as well as for Windows platforms.
This section describes how MySQL relates to the ANSI/ISO SQL standards. MySQL Server has many extensions to the SQL standard, and here you will find out what they are and how to use them. You will also find information about functionality missing from MySQL Server, and how to work around some differences.
The SQL standard has been evolving since 1986 and several versions exist. In this manual, ``SQL-92'' refers to the standard released in 1992, ``SQL:1999'' refers to the standard released in 1999, and ``SQL:2003'' refers to the current version of the standard. We use the phrase ``the SQL standard'' to mean the current version of the SQL Standard at any time.
Our goal is to not restrict MySQL Server usability for any usage without a very good reason for doing so. Even if we don't have the resources to perform development for every possible use, we are always willing to help and offer suggestions to people who are trying to use MySQL Server in new territories.
One of our main goals with the product is to continue to work toward
compliance with the SQL standard, but without sacrificing speed or reliability.
We are not afraid to add extensions to SQL or support for non-SQL
features if this greatly increases the usability of MySQL Server for a large
segment of our user base.
The HANDLER
interface in MySQL Server 4.0 is an example of this
strategy. See section 14.1.3 HANDLER
Syntax.
We will continue to support transactional and non-transactional databases to satisfy both mission-critical 24/7 usage and heavy Web or logging usage.
MySQL Server was originally designed to work with medium size databases (10-100 million rows, or about 100MB per table) on small computer systems. Today MySQL Server handles terabyte-size databases, but the code can also be compiled in a reduced version suitable for hand-held and embedded devices. The compact design of the MySQL server makes development in both directions possible without any conflicts in the source tree.
Currently, we are not targeting realtime support, although MySQL replication capabilities already offer significant functionality.
Database cluster support now exists through third-party clustering solutions as well as the integration of our acquired NDB Cluster technology into a new storage engine, available from version 4.1.2. See section 17 MySQL Cluster.
We are also looking at providing XML support in the database server.
We are aiming toward supporting the full ANSI/ISO SQL standard, but without making concessions to speed and quality of the code.
ODBC levels 0-3.51.
The MySQL server can operate in different SQL modes, and can apply these modes differentially for different clients. This allows applications to tailor server operation to their own requirements.
Modes define what SQL syntax MySQL should support and what kind of validation checks it should perform on the data. This makes it easier to use MySQL in a lot of different environments and to use MySQL together with other database servers.
You can set the default SQL mode by starting mysqld
with the
--sql-mode="modes"
option. Beginning with MySQL 4.1, you can also
change the mode after startup time by setting the sql_mode
variable
with a SET [SESSION|GLOBAL] sql_mode='modes'
statement.
For more information on setting the server mode, see section 5.2.2 The Server SQL Mode.
You can tell mysqld
to use the ANSI mode with the --ansi
startup option. See section 5.2.1 mysqld
Command-Line Options.
Running the server in ANSI mode is the same as starting it with these options
(specify the --sql_mode
value on a single line):
--transaction-isolation=SERIALIZABLE --sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES, IGNORE_SPACE,ONLY_FULL_GROUP_BY
In MySQL 4.1, you can achieve the same effect with these two statements
(specify the sql_mode
value on a single line):
SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE; SET GLOBAL sql_mode = 'REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES, IGNORE_SPACE,ONLY_FULL_GROUP_BY';
See section 1.8.2 Selecting SQL Modes.
In MySQL 4.1.1, the sql_mode
options shown can be also be set with
this statement:
SET GLOBAL sql_mode='ansi';
In this case, the value of the sql_mode
variable will be set to all
options that are relevant for ANSI mode. You can check the result like this:
mysql> SET GLOBAL sql_mode='ansi'; mysql> SELECT @@global.sql_mode; -> 'REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES, IGNORE_SPACE,ONLY_FULL_GROUP_BY,ANSI';
MySQL Server 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 Server 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 `!' character, the syntax within the comment will be executed only if the MySQL version is equal to or newer than the specified version number:
CREATE /*!32302 TEMPORARY */ TABLE t (a INT);
This means that if you have Version 3.23.02 or newer, MySQL
Server will use the TEMPORARY
keyword.
The following descriptions list MySQL extensions, organized by category.
MyISAM
or ISAM
storage engines.
For example, to rename a MyISAM
table, rename the `.MYD',
`.MYI', and `.frm' files to which the table corresponds.
db_name.tbl_name
syntax. Some SQL servers provide
the same functionality but call this User space
.
MySQL Server doesn't support tablespaces such as used in statements like this:
CREATE TABLE ralph.my_table...IN my_tablespace
.
ANALYZE TABLE
, CHECK TABLE
, OPTIMIZE TABLE
, and
REPAIR TABLE
statements.
CREATE DATABASE
and DROP DATABASE
statements.
See section 14.2.3 CREATE DATABASE
Syntax.
DO
statement.
EXPLAIN SELECT
to get a description of how tables are joined.
FLUSH
and RESET
statements.
SET
statement. See section 14.5.3.1 SET
Syntax.
SHOW
statement.
See section 14.5.3 SET
and SHOW
Syntax.
LOAD DATA INFILE
. In many cases, this syntax is compatible with
Oracle's LOAD DATA INFILE
. See section 14.1.5 LOAD DATA INFILE
Syntax.
RENAME TABLE
. See section 14.2.9 RENAME TABLE
Syntax.
REPLACE
instead of DELETE
+ INSERT
.
See section 14.1.6 REPLACE
Syntax.
CHANGE col_name
, DROP col_name
, or DROP
INDEX
, IGNORE
or RENAME
in an ALTER TABLE
statement.
Use of multiple ADD
, ALTER
, DROP
, or CHANGE
clauses in an ALTER TABLE
statement.
See section 14.2.2 ALTER TABLE
Syntax.
INDEX
or KEY
in a CREATE TABLE
statement. See section 14.2.5 CREATE TABLE
Syntax.
TEMPORARY
or IF NOT EXISTS
with CREATE TABLE
.
IF EXISTS
with DROP TABLE
.
DROP TABLE
statement.
ORDER BY
and LIMIT
clauses of the UPDATE
and
DELETE
statements.
INSERT INTO ... SET col_name = ...
syntax.
DELAYED
clause of the INSERT
and REPLACE
statements.
LOW_PRIORITY
clause of the INSERT
, REPLACE
,
DELETE
, and UPDATE
statements.
INTO OUTFILE
and STRAIGHT_JOIN
in a SELECT
statement. See section 14.1.7 SELECT
Syntax.
SQL_SMALL_RESULT
option in a SELECT
statement.
GROUP BY
part.
This gives better performance for some very specific, but quite normal
queries.
See section 13.9 Functions and Modifiers for Use with GROUP BY
Clauses.
ASC
and DESC
with GROUP BY
.
:=
assignment
operator:
mysql> SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg -> FROM test_table; mysql> SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;
MEDIUMINT
, SET
, ENUM
, and the
different BLOB
and TEXT
types.
AUTO_INCREMENT
, BINARY
, NULL
,
UNSIGNED
, and ZEROFILL
.
||
and &&
operators to mean
logical OR and AND, as in the C programming language. In MySQL Server,
||
and OR
are synonyms, as are &&
and AND
.
Because of this nice syntax, MySQL Server doesn't support
the standard 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 Server.
COUNT(DISTINCT list)
where list
has more than one element.
BINARY
attribute or use the BINARY
cast, which causes
comparisons to be done using the underlying character code values rather
then a lexical ordering.
%
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 that returns the most recent
AUTO_INCREMENT
value.
See section 13.8.3 Information Functions.
LIKE
is allowed on numeric columns.
REGEXP
and NOT REGEXP
extended regular expression
operators.
CONCAT()
or CHAR()
with one argument or more than two
arguments. (In MySQL Server, 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()
, and
WEEKDAY()
functions.
TRIM()
to trim substrings. Standard SQL supports removal
of single characters only.
GROUP BY
functions STD()
, BIT_OR()
,
BIT_AND()
, BIT_XOR()
, and GROUP_CONCAT()
.
See section 13.9 Functions and Modifiers for Use with GROUP BY
Clauses.
For a prioritized list indicating when new extensions will be added to MySQL Server, you should consult the online MySQL TODO list at http://dev.mysql.com/doc/mysql/en/TODO.html. That is the latest version of the TODO list in this manual. See section 1.6 MySQL and the Future (the TODO).
We try to make MySQL Server follow the ANSI SQL standard and the ODBC SQL standard, but MySQL Server performs operations differently in some cases:
VARCHAR
columns, trailing spaces are removed when the value is
stored. See section 1.8.7 Known Errors and Design Deficiencies in MySQL.
CHAR
columns are silently converted to VARCHAR
columns when you define a table or alter its structure.
See section 14.2.5.1 Silent Column Specification Changes.
REVOKE
statement to revoke
privileges for a table. See section 14.5.1.2 GRANT
and REVOKE
Syntax.
MySQL 4.1 supports subqueries and derived tables.
A ``subquery'' is a SELECT
statement nested within another statement.
A ``derived table'' (an unnamed view) is a subquery in the FROM
clause
of another statement.
See section 14.1.8 Subquery Syntax.
For MySQL versions older than 4.1, most subqueries can be rewritten using joins or other methods. See section 14.1.8.11 Rewriting Subqueries as Joins for Earlier MySQL Versions for examples that show how to do this.
SELECT INTO TABLE
MySQL Server doesn't support the Sybase SQL extension:
SELECT ... INTO TABLE ...
. Instead, MySQL Server supports the
standard SQL syntax INSERT INTO ... SELECT ...
, which is basically
the same thing. See section 14.1.4.1 INSERT ... SELECT
Syntax.
INSERT INTO tbl_temp2 (fld_id) SELECT tbl_temp1.fld_order_id FROM tbl_temp1 WHERE tbl_temp1.fld_order_id > 100;
Alternatively, you can use SELECT INTO OUTFILE ...
or
CREATE TABLE ... SELECT
.
From version 5.0, MySQL supports SELECT ... INTO
with user
variables. The same syntax may also be used inside stored procedures using
cursors and local variables.
See section 20.1.6.3 SELECT ... INTO
Statement.
MySQL Server (version 3.23-max and all versions 4.0 and above) supports
transactions with the InnoDB
and BDB
transactional storage engines.
InnoDB
provides full ACID
compliance.
See section 15 MySQL Storage Engines and Table Types.
The other non-transactional storage engines in MySQL Server (such as
MyISAM
) follow a different paradigm for data integrity called
``atomic operations.'' In transactional terms, MyISAM
tables effectively always operate in AUTOCOMMIT=1
mode.
Atomic operations often offer comparable integrity with higher performance.
With MySQL Server supporting both paradigms, you can decide whether your applications are best served by the speed of atomic operations or the use of transactional features. This choice can be made on a per-table basis.
As noted, the trade-off for transactional versus non-transactional table
types lies mostly in performance. Transactional tables have significantly
higher memory and diskspace requirements, and more CPU overhead.
On the other hand, transactional table types such as InnoDB
also
offer many significant features. MySQL Server's modular design allows the
concurrent use of different storage engines to suit different
requirements and deliver optimum performance in all situations.
But how do you use the features of MySQL Server to maintain rigorous
integrity even with the non-transactional MyISAM
tables, and how
do these features compare with the transactional table types?
ROLLBACK
rather than
COMMIT
in critical situations, transactions are more
convenient. Transactions also 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.
If you use non-transactional tables,
MySQL Server in almost all cases allows you to resolve 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 an inconsistency occurs. Note that just by using the
MySQL log or even adding one extra log, you can normally fix tables
perfectly with no data integrity loss.
LOCK TABLES
or atomic updates, ensuring
that you never will get an automatic abort from the server, which is
a common problem with transactional database systems.
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. However, even if you are new to the atomic operations paradigm, or more familiar with transactions, do consider the speed benefit that non-transactional tables can offer on the order of three to five times the speed of the fastest and most optimally tuned transactional tables.
In situations where integrity is of highest importance, MySQL Server offers
transaction-level reliability and integrity even for non-transactional tables.
If you lock tables with LOCK TABLES
, all updates will stall
until any integrity checks are made. If you obtain a READ LOCAL
lock
(as opposed to a write lock) for a table that allows concurrent inserts at the
end of the table, reads are allowed, as are inserts by other clients.
The new inserted records will not be seen by the
client that has the read lock until it releases the lock.
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. See section 14.1.4.2 INSERT DELAYED
Syntax.
``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 with transactional tables if you are not very careful). MySQL Server also guarantees that there will not be any dirty reads.
Following are some techniques for working with non-transactional tables:
LOCK TABLES
, and you don't need cursors to update
records on the fly.
ROLLBACK
, you can use the following strategy:
LOCK TABLES
to lock all the tables you want to access.
UNLOCK TABLES
to release your locks.
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
has been changed by another user.'' Then we show the old row versus the new
row in a window so that the user can decide which version of the customer
record to 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+125; UPDATE customer SET customer_date='current_date', address='new address', phone='new phone', money_owed_to_us=money_owed_to_us-125 WHERE customer_id=id AND address='old address' AND phone='old phone';This is very efficient and works even if another client has changed the values in the
pay_back
or money_owed_to_us
columns.
LOCK TABLES
and/or ROLLBACK
for the purpose of managing unique identifiers. This can be handled much
more efficiently without locking or rolling back by using an
AUTO_INCREMENT
column and either the
LAST_INSERT_ID()
SQL function or the mysql_insert_id()
C API function.
See section 13.8.3 Information Functions.
See section 21.2.3.32 mysql_insert_id()
.
You can generally code around the need for row-level locking. Some situations
really do need it, and InnoDB
tables support row-level locking. With
MyISAM
tables, you can use a flag column in the table and do something
like the following:
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 though MySQL Server changed the preceding query to:
UPDATE tbl_name SET row_flag=1 WHERE id=ID AND row_flag <> 1;
Stored procedures are implemented in MySQL version 5.0. See section 20 Stored Procedures and Functions.
Triggers are scheduled for implementation in MySQL version 5.1. A ``trigger'' is effectively a type of stored procedure, one that is invoked when a particular event occurs. For example, you could set up a stored procedure that is triggered each time a record is deleted from a transactional table, and that stored procedure automatically deletes the corresponding customer from a customer table when all their transactions are deleted.
In MySQL Server 3.23.44 and up, the InnoDB
storage engine supports
checking of foreign key constraints, including CASCADE
, ON
DELETE
, and ON UPDATE
. See section 16.7.4 FOREIGN KEY
Constraints.
For storage engines other than InnoDB
, MySQL Server parses the
FOREIGN KEY
syntax in CREATE TABLE
statements, but does not
use or store it. In the future, the implementation will be
extended to store this information in the table specification file so that it
may be retrieved by mysqldump
and ODBC. At a later stage,
foreign key constraints will be implemented for MyISAM
tables as well.
Foreign key enforcement offers several benefits to database developers:
Do keep in mind that these benefits come at the cost of additional overhead for the database server to perform the necessary checks. Additional checking by the server affects performance, which for some applications may be sufficiently undesirable as to be avoided if possible. (Some major commercial applications have coded the foreign-key logic at the application level for this reason.)
MySQL gives database developers the choice of which approach to use. If you
don't need foreign keys and want to avoid the overhead associated with
enforcing referential integrity, you can choose another table type instead,
such as MyISAM
. (For example, the MyISAM
storage engine offers
very fast performance for applications that perform only INSERT
and
SELECT
operations, because the inserts can be performed concurrently
with retrievals. See section 7.3.2 Table Locking Issues.)
If you choose not to take advantage of referential integrity checks, keep the following considerations in mind:
ON DELETE
is the only referential integrity capability an
application needs, note that as of MySQL Server 4.0, you can use
multiple-table DELETE
statements to delete rows from many
tables with a single statement. See section 14.1.1 DELETE
Syntax.
ON DELETE
is to add
the appropriate DELETE
statement to your application when you
delete records from a table that has a foreign key. In practice, this is often
as quick as using foreign keys, and is more portable.
Be aware that the use of foreign keys can in some instances lead to problems:
FOREIGN KEY
Constraints.
As of MySQL 4.1.1,
mysqldump
generates dump files that take advantage of this
capability automatically when reloaded.)
Note that foreign keys in SQL are used to check and enforce referential
integrity, not to join tables. If you want to get results from multiple
tables from a SELECT
statement, you do this by performing a join
between them:
SELECT * FROM t1, t2 WHERE t1.id = t2.id;
See section 14.1.7.1 JOIN
Syntax. See section 3.6.6 Using Foreign Keys.
The FOREIGN KEY
syntax without ON DELETE ...
is often used
by ODBC applications to produce automatic WHERE
clauses.
Views currently are being implemented, and will shortly appear in the 5.0
version of MySQL Server.
Unnamed views (derived tables, a subquery in the FROM
clause of a SELECT
) are already implemented in version 4.1.
Unqualified union views (SELECT ... UNION SELECT ...
are also
available through the MERGE
table feature.
See section 15.2 The MERGE
Storage Engine.
Historically, MySQL Server has been most used in applications and on Web systems where the application writer has full control over database usage. Usage has shifted over time, and so we find that an increasing number of users now regard views as an important feature.
Views are useful for allowing users to access a set of relations (tables) as if it were a single table, and limiting their access to just that. Views can also be used to restrict access to rows (a subset of a particular table). For access control to columns, you can also use the sophisticated privilege system in MySQL Server. See section 5.4 The MySQL Access Privilege System.
Many DBMS don't allow updates to a view. Instead, you have to perform the updates on the individual tables. In designing an implementation of views, our goal, as much as is possible within the confines of SQL, is full compliance with ``Codd's Rule #6'' for relational database systems: All views that are theoretically updatable, should in practice also be updatable.
Some other SQL databases use `--' to start comments.
MySQL Server uses `#' as the start comment character. You can also use
the C comment style /* this is a comment */
with MySQL Server.
See section 10.5 Comment Syntax.
MySQL Server 3.23.3 and above support the `--' comment style,
provided the comment is followed by a space (or by a control character such
as a newline). The requirement for a space is to prevent 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 account SET credit=credit-!payment!
Think about what happens if the value of payment
is a negative value
such as -1
:
UPDATE account SET credit=credit--1
credit--1
is a legal expression in SQL, but if --
is interpreted
as the start of a comment, part of the expression is discarded. The result is a
statement that has a completely different meaning than intended:
UPDATE account SET credit=credit
The statement produces no change in value at all! This illustrates that allowing comments to start with `--' can have serious consequences.
Using our implementation of this method of commenting in MySQL Server
3.23.3 and up, credit--1
is actually safe.
Another safe feature is that the mysql
command-line client
removes all lines that start with `--'.
The following information is relevant only if you are running a MySQL version earlier than 3.23.3:
If you have an SQL program in a text file that contains `--'
comments, you should use the replace
utility as follows to convert the
comments to use `#' characters:
shell> replace " --" " #" < text-file-with-funny-comments.sql \ | mysql db_name
instead of the usual:
shell> mysql db_name < 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
MySQL allows you to work with both transactional tables that allow rollback and non-transactional tables that do not, so constraint handling is a bit different in MySQL than in other databases.
We have to handle the case when you have updated a lot of rows in a non-transactional table that cannot roll back when an error occurs.
The basic philosophy is to try to give an error for anything that we can detect at compile time but try to recover from any errors we get at runtime. We do this in most cases, but not yet for all. See section 1.6.4 New Features Planned for the Near Future.
The options MySQL has when an error occurs are to stop the statement in the middle or to recover as well as possible from the problem and continue.
The following sections describe what happens for the different types of constraints.
PRIMARY KEY
/ UNIQUE
Normally you will get an error when you try to INSERT
or
UPDATE
a row that causes a primary key, unique key, or foreign key
violation. If you are using a transactional storage engine such as
InnoDB
, MySQL will automatically roll back the transaction. If you are
using a non-transactional storage engine, MySQL will stop at the incorrect
row and leave any remaining rows unprocessed.
To make life easier, MySQL supports an IGNORE
keyword for
most commands that can cause a key violation (such as INSERT IGNORE
and UPDATE IGNORE
). In this case, MySQL will ignore any key
violation and continue with processing the next row. You can get
information about what MySQL did with the mysql_info()
C API function.
See section 21.2.3.30 mysql_info()
.
In MySQL 4.1 and up, you also can use the SHOW WARNINGS
statement.
See section 14.5.3.20 SHOW WARNINGS
Syntax.
Note that, for the moment, only InnoDB
tables support foreign keys.
See section 16.7.4 FOREIGN KEY
Constraints.
Foreign key support in MyISAM
tables is scheduled for implementation
in MySQL 5.1.
NOT NULL
and DEFAULT
ValuesTo be able to support easy handling of non-transactional tables, all columns in MySQL have default values.
If you insert an ``incorrect'' value into a column, such as a NULL
into a NOT NULL
column or a too-large numerical value into a
numerical column, MySQL sets the column to the ``best possible value''
instead of producing an error:
NULL
into a column that doesn't take NULL
values, MySQL Server stores 0 or ''
(the empty string) instead. This
last behavior can, for single-row inserts, be changed when MySQL is built by
using the -DDONT_USE_DEFAULT_FIELDS
compile option.) See section 2.3.2 Typical configure
Options. This causes INSERT
statements
to generate an error unless you explicitly specify values for all columns
that require a non-NULL
value.
DATE
and
DATETIME
columns (like '2000-02-31'
or '2000-02-00'
).
The idea is that it's not the job of the SQL server to validate dates. If
MySQL can store a date value and retrieve exactly the same value, MySQL
stores it as given. If the date is totally wrong (outside the server's
ability to store it), the special date value '0000-00-00'
is stored
in the column instead.
The reason for the preceding rules is that we can't check these conditions until the query has begun executing. We can't just roll back if we encounter a problem after updating a few rows, because the table type may not support rollback. The option of terminating the statement is not that good; in this case, the update would be ``half done,'' which is probably the worst possible scenario. In this case, it's better to ``do the best you can'' and then continue as if nothing happened.
This means that you should generally not use MySQL to check column content. Instead, the application should ensure that it passes only legal values to MySQL.
In MySQL 5.0, we plan to improve this by providing warnings when automatic column conversions occur, plus an option to let you roll back statements that attempt to perform a disallowed column value assignment, as long as the statement uses only transactional tables.
ENUM
and SET
In MySQL 4.x, ENUM
is not a real constraint, but is a more efficient
way to define columns that can contain only a given set of values.
This is for the same reasons that NOT NULL
is not honored.
See section 1.8.6.2 Constraint NOT NULL
and DEFAULT
Values.
If you insert an incorrect value into an ENUM
column, it is set to
the reserved enumeration value of 0
, which is displayed as an empty
string in string context. See section 12.4.3 The ENUM
Type.
If you insert an incorrect value into a SET
column, the incorrect value
is ignored. For example, if the column can contain the values
'a'
, 'b'
, and 'c'
, an attempt to assign 'a,x,b,y'
results in a value of 'a,b'
.
See section 12.4.4 The SET
Type.
The following known errors or bugs are not fixed in MySQL 3.23 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.''
LOCK TABLE
to lock
multiple tables and then in the same connection use DROP TABLE
to
drop one of them while another thread is trying to lock it. (To break the
deadlock, you can use KILL
to terminate any of the threads involved.)
This issue is resolved as of MySQL 4.0.12.
SELECT MAX(key_column) FROM t1,t2,t3...
where one of the tables are
empty doesn't return NULL
but instead returns the maximum value for the
column. This issue is resolved as of MySQL 4.0.11.
DELETE FROM heap_table
without a WHERE
clause doesn't work on
a locked HEAP
table.
The following known errors or bugs are not fixed in MySQL 4.0 because fixing them would involve changing a lot of code that could introduce other even worse bugs. The bugs are also classified as ``not fatal'' or ``bearable.''
UNION
, the first SELECT
determines the type,
max_length
, and NULL
properties for the resulting
columns. This issue is resolved as of MySQL 4.1.1; the property values are
based on the rows from all UNION
parts.
DELETE
with many tables, you can't refer to tables to be
deleted through an alias. This is fixed as of MySQL 4.1.
UNION ALL
and UNION DISTINCT
in the same query.
If you use ALL
for one UNION
, it is used for all
of them.
The following problems are known and fixing them is a high priority:
lower_case_table_names=2
(which enables
MySQL to remember the used case for databases and table names) MySQL
will not on case insensitive systems remember the used case for database
names for the function DATABASE()
or in various logs.
FOREIGN KEY
constraint doesn't work in replication because
the constraint may have another name on the slave.
REPLACE
(and LOAD DATA
with the REPLACE
option) does not
trigger ON DELETE CASCADE
.
DISTINCT
with ORDER BY
doesn't work inside GROUP_CONCAT()
if you don't use all and only those columns that are in the
DISTINCT
list.
GROUP_CONCAT()
doesn't work with BLOB
/TEXT
columns
when you use DISTINCT
or ORDER BY
inside
GROUP_CONCAT()
. To work around this limitation, use
MID(expr, 1, 255)
instead.
DROP TABLE
command before the table is
used in the transaction itself. We plan to fix this in 5.0 by
having the DROP TABLE
wait until the table is not used in any
transaction.
FLUSH TABLES WITH READ LOCK
does not block CREATE TABLE
or
COMMIT
, which may cause a problem with the binary log position when
doing a full backup of tables and the binary log.
ANALYZE TABLE
on a BDB
table may in some cases make the table
unusable until you restart mysqld
. If this happens, you will
see errors of the following form in the MySQL error file:
001207 22:07:56 bdb: log_flush: LSN past current end-of-log
FROM
clause of a SELECT
statement, but silently
ignores them. The reason for not giving an error is that many clients
that automatically generate queries add parentheses in the FROM
clause even where they are not needed.
RIGHT JOINS
or combining LEFT
and
RIGHT
join in the same query may not give a correct answer because
MySQL only generates NULL
rows for the table preceding a LEFT
or
before a RIGHT
join. This will be fixed in 5.0 at the same time
we add support for parentheses in the FROM
clause.
ALTER TABLE
on a BDB
table on which you are
running multiple-statement transactions until all those transactions complete.
(The transaction will probably be ignored.)
ANALYZE TABLE
, OPTIMIZE TABLE
, and REPAIR TABLE
may
cause problems on tables for which you are using INSERT DELAYED
.
LOCK TABLE ...
and FLUSH TABLES ...
doesn't
guarantee that there isn't a half-finished transaction in progress on the
table.
BDB
tables are a bit slow to open. If you have many BDB
tables
in a database, it will take a long time to use the mysql
client on
the database if you are not using the -A
option or if you are using
rehash
. This is especially notable when you have a large table cache.
CREATE ... SELECT
or
INSERT ... SELECT
statements that
insert zero or NULL
values into an AUTO_INCREMENT
column.
DELETE
if you are
deleting rows from a table that has foreign keys with ON DELETE
CASCADE
properties.
REPLACE ... SELECT
,
INSERT IGNORE ... SELECT
if you have
duplicate key values in the inserted data.
ORDER BY
clause guaranteeing a deterministic order.
For example, for INSERT ... SELECT
with no ORDER
BY
, the SELECT
may return rows in a different order
(which will result in a row having different ranks, hence getting a
different number in the AUTO_INCREMENT
column),
depending on the choices made by the optimizers on the master and
slave. A query will be optimized differently on the master and slave only if:
OPTIMIZE TABLE
was run on the master tables and not on
the slave tables. (To fix this, OPTIMIZE TABLE
, ANALYZE TABLE
,
and REPAIR TABLE
are written to the binary log as of MySQL 4.1.1).
InnoDB
on the master,
but MyISAM
on the slave if the slave has less available disk
space.)
key_buffer_size
, and so on) are different on
the master and slave.
mysqlbinlog|mysql
.
The easiest way to avoid this problem in all cases is to add an
ORDER BY
clause to
such non-deterministic queries to ensure that the rows are always
stored or modified in the same order.
In future MySQL versions, we will automatically add an ORDER BY
clause when needed.
The following problems are known and will be fixed in due time:
--log-bin=old_host_name-bin
if you change your hostname to something
else. Another option is to just rename the old files to reflect your
hostname change. See section 5.2.1 mysqld
Command-Line Options.
mysqlbinlog
will not delete temporary files left after a
LOAD DATA INFILE
command. See section 8.5 The mysqlbinlog
Binary Log Utility.
RENAME
doesn't work with TEMPORARY
tables or tables used in a
MERGE
table.
RPAD()
function in a query that has to be
resolved by using a temporary table, all resulting strings will
have rightmost spaces removed. This is an example of such a query:
SELECT RPAD(t1.column1, 50, ' ') AS f2, RPAD(t2.column2, 50, ' ') AS f1 FROM table1 as t1 LEFT JOIN table2 AS t2 ON t1.record=t2.joinID ORDER BY t2.record;The final result of this bug is that you will not be able to get spaces on the right side of the resulting values. The problem also occurs for any other string function that adds spaces to the right. The reason for this is due to the fact that
HEAP
tables, which are used
first for temporary tables, are not capable of handling VARCHAR
columns.
This behavior exists in all versions of MySQL.
It will be fixed in one of the 4.1 series releases.
CHAR(255)
) in table names, column names, or enumerations.
This is scheduled to be fixed in version 5.1 when we have new table
definition format files.
SET CHARACTER SET
, you can't use translated
characters in database, table, and column names.
ESCAPE
in LIKE
... ESCAPE
.
DECIMAL
column in which the same number is stored in
different formats (for example, +01.00
, 1.00
, 01.00
),
GROUP BY
may regard each value as a different value.
BLOB
values can't ``reliably'' be used in GROUP BY
or
ORDER BY
or DISTINCT
. Only the first max_sort_length
bytes are used when comparing BLOB
values in these cases.
The default value of max_sort_length
value is 1024. It can be changed
at server startup time. A workaround for most cases is to use a substring.
For example:
SELECT DISTINCT LEFT(blob_col,2048) FROM tbl_name
.
BIGINT
or DOUBLE
(both are
normally 64 bits long). Which precision you get depends on the function.
The general rule is that bit functions are done with BIGINT
precision, IF
and ELT()
with BIGINT
or DOUBLE
precision, and the rest with DOUBLE
precision. You should try to
avoid using unsigned long long values if they resolve to be bigger than
63 bits (9223372036854775807) for anything other than bit fields.
MySQL Server 4.0 has better BIGINT
handling than 3.23.
BLOB
and TEXT
columns, automatically
have all trailing spaces removed when retrieved. For CHAR
types, this
is okay. The bug is
that in MySQL Server, VARCHAR
columns are treated the same way.
ENUM
and SET
columns in one table.
MIN()
, MAX()
, and other aggregate functions, MySQL
currently compares ENUM
and SET
columns by their string
value rather than by the string's relative position in the set.
mysqld_safe
redirects all messages from mysqld
to the
mysqld
log. One problem with this is that if you execute
mysqladmin refresh
to close and reopen the log,
stdout
and stderr
are still redirected to the old log.
If you use --log
extensively, you should edit mysqld_safe
to
log to `host_name.err' instead of `host_name.log' so that you can
easily reclaim the space for the old log by deleting the old one and
executing mysqladmin refresh
.
UPDATE
statement, columns are updated from left to right. If
you refer to an updated column, you get the updated value instead of the
original value. For example, the following statement increments KEY
by 2
, not 1
:
mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1;
mysql> SELECT * FROM temp_table, temp_table AS t2; ERROR 1137: Can't reopen table: 'temp_table'
DISTINCT
differently when you are using
``hidden'' columns in a join than when you are not. In a join, hidden
columns are counted as part of the result (even if they are not shown),
whereas in normal queries, hidden columns don't participate in the
DISTINCT
comparison. We will probably change this in the future to
never compare the hidden columns when executing DISTINCT
.
An example of this is:
SELECT DISTINCT mp3id FROM band_downloads WHERE userid = 9 ORDER BY id DESC;and
SELECT DISTINCT band_downloads.mp3id FROM band_downloads,band_mp3 WHERE band_downloads.userid = 9 AND band_mp3.id = band_downloads.mp3id ORDER BY band_downloads.id DESC;In the second case, you might in MySQL Server 3.23.x get two identical rows in the result set (because the values in the hidden
id
column may differ).
Note that this happens only for queries where you don't have the
ORDER BY
columns in the result.
PROCEDURE
on a query that returns an empty set,
in some cases the PROCEDURE
will not transform the columns.
MERGE
doesn't check whether the underlying
tables are of compatible types.
ALTER TABLE
first to add a UNIQUE
index to a
table used in a MERGE
table and then to
add a normal index on the MERGE
table, the key order will be
different for the tables if there was an old key that was not unique in the
table. This is because ALTER TABLE
puts UNIQUE
indexes before
normal indexes to be able to detect duplicate keys as early as possible.
The following are known bugs in earlier versions of MySQL:
LOCK TABLE
with WRITE
.
FLUSH TABLES
.
UPDATE
that updated a key with
a WHERE
on the same key may have failed because the key was used to
search for records and the same row may have been found multiple times:
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;A workaround is to use:
UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;This will work because MySQL Server will not use an index on expressions in the
WHERE
clause.
For information about platform-specific bugs, see the installation and porting instructions in section 2.6 Operating System-Specific Notes and section D Porting to Other Systems.
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