Table of Contents
The MySQL™ 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. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. MySQL is a trademark of Oracle Corporation and/or its affiliates, and shall not be used by Customer without Oracle's express written authorization. Other names may be trademarks of their respective owners.
The MySQL software is Dual Licensed. Users can choose to use the MySQL software as an Open Source product under the terms of the GNU General Public License (http://www.fsf.org/licenses/) or can purchase a standard commercial license from Oracle. See http://www.mysql.com/company/legal/licensing/ for more information on our licensing policies.
The following list describes some sections of particular interest in this manual:
For a discussion of MySQL Database Server capabilities, see Section 1.3.2, “The Main Features of MySQL”.
For an overview of new MySQL features, see Section 1.4, “What Is New in MySQL 5.5”. For information about the changes in each version, see the Release Notes.
For installation instructions, see Chapter 2, Installing and Upgrading MySQL. For information about upgrading MySQL, see Section 2.11.1, “Upgrading MySQL”.
For a tutorial introduction to the MySQL Database Server, see Chapter 3, Tutorial.
For information about configuring and administering MySQL Server, see Chapter 5, MySQL Server Administration.
For information about security in MySQL, see Chapter 6, Security.
For information about setting up replication servers, see Chapter 17, Replication.
For information about MySQL Enterprise, the commercial MySQL release with advanced features and management tools, see Chapter 25, MySQL Enterprise Edition.
For answers to a number of questions that are often asked concerning the MySQL Database Server and its capabilities, see Appendix A, MySQL 5.5 Frequently Asked Questions.
For a history of new features and bug fixes, see the Release Notes.
To report problems or bugs, please use the instructions at
Section 1.6, “How to Report Bugs or Problems”. If you find a sensitive security
bug in MySQL Server, please let us know immediately by sending an
email message to <secalert_us@oracle.com>. Exception:
Support customers should report all problems, including security
bugs, to Oracle Support.
This is the Reference Manual for the MySQL Database System,
version 5.5, through release 5.5.46.
Differences between minor versions of MySQL 5.5 are
noted in the present text with reference to release numbers
(5.5.x). For license
information, see the Legal
Notices. This product may contain third-party code. For
license information on third-party code, see
Appendix E, Licenses for Third-Party Components.
This manual is not intended for use with older versions of the MySQL software due to the many functional and other differences between MySQL 5.5 and previous versions. If you are using an earlier release of the MySQL software, please refer to the appropriate manual. For example, MySQL 5.1 Reference Manual covers the 5.1 series of MySQL software releases.
If you are using MySQL 5.6, please refer to the MySQL 5.6 Reference Manual.
Because this manual serves as a reference, it does not provide general instruction on SQL or relational database concepts. It also does 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 there, including HTML, PDF, and EPUB versions.
The Reference Manual source files are written in DocBook XML format. The HTML version and other formats are produced automatically, primarily using the DocBook XSL stylesheets. For information about DocBook, see http://docbook.org/
If you have questions about using MySQL, you can ask them using our mailing lists or forums. See Section 1.5.1, “MySQL Mailing Lists”, and Section 1.5.2, “MySQL Community Support at the MySQL Forums”. If you have suggestions concerning additions or corrections to the manual itself, please send them to the http://www.mysql.com/company/contact/.
This manual was originally written by David Axmark and Michael “Monty” Widenius. It is maintained by the MySQL Documentation Team, consisting of Chris Cole, Paul DuBois, Edward Gilmore, Stefan Hinz, David Moss, Philip Olson, Daniel Price, Daniel So, and Jon Stephens.
This manual uses certain typographical conventions:
Text in this style is used for SQL
statements; database, table, and column names; program listings
and source code; and environment variables. Example: “To
reload the grant tables, use the
FLUSH
PRIVILEGES statement.”
Text in this style indicates input that
you type in examples.
Text in this style indicates the names of executable programs and scripts, examples being mysql (the MySQL command-line client program) and mysqld (the MySQL server executable).
Text in this style is used for
variable input for which you should substitute a value of your
own choosing.
Text in this style is used for emphasis.
Text in this style is used in table headings and to convey especially strong emphasis.
Text in this style is used to indicate a
program option that affects how the program is executed, or that
supplies information that is needed for the program to function
in a certain way. Example: “The
--host option (short form -h)
tells the mysql client program the hostname
or IP address of the MySQL server that it should connect
to”.
File names and directory names are written like this: “The
global my.cnf file is located in the
/etc directory.”
Character sequences are written like this: “To specify a
wildcard, use the ‘%’
character.”
When commands are shown that are meant to be executed from within a
particular program, the prompt shown preceding the command indicates
which command to use. For example, shell>
indicates a command that you execute from your login shell,
root-shell> is similar but should be executed
as root, and mysql>
indicates a statement that you execute from the
mysql client program:
shell>type a shell command hereroot-shell>type a shell command asmysql>rootheretype a mysql statement here
In some areas different systems may be distinguished from each other
to show that commands should be executed in two different
environments. For example, while working with replication the
commands might be prefixed with master and
slave:
master>type a mysql command on the replication master hereslave>type a mysql command on the replication slave here
The “shell” is your command interpreter. On Unix, this is typically a program such as sh, csh, or bash. 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 any lettercase. This manual uses uppercase.
In syntax descriptions, square brackets
(“[” and
“]”) 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,
SELECT ... INTO
OUTFILE is shorthand for the form of
SELECT statement that has an
INTO OUTFILE clause following other parts of the
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:
RESETreset_option[,reset_option] ...
Commands for setting shell variables are shown using Bourne shell
syntax. For example, the sequence to set the CC
environment variable and run the configure
command looks like this in Bourne shell syntax:
shell> CC=gcc ./configure
If you are using csh or tcsh, you must issue commands somewhat differently:
shell>setenv CC gccshell>./configure
MySQL, the most popular Open Source SQL database management system, is developed, distributed, and supported by Oracle Corporation.
The MySQL Web site (http://www.mysql.com/) provides the latest information about MySQL software.
MySQL is a database management system.
A database is a structured collection of data. It may be anything from a simple shopping list to a picture gallery or the vast amounts of information in a corporate network. To add, access, and process data stored in a computer database, you need a database management system such as MySQL Server. Since computers are very good at handling large amounts of data, database management systems play a central role in computing, as standalone utilities, or as parts of other applications.
MySQL databases are relational.
A relational database stores data in separate tables rather than putting all the data in one big storeroom. The database structures are organized into physical files optimized for speed. The logical model, with objects such as databases, tables, views, rows, and columns, offers a flexible programming environment. You set up rules governing the relationships between different data fields, such as one-to-one, one-to-many, unique, required or optional, and “pointers” between different tables. The database enforces these rules, so that with a well-designed database, your application never sees inconsistent, duplicate, orphan, out-of-date, or missing data.
The SQL part of “MySQL” stands for “Structured Query Language”. SQL is the most common standardized language used to access databases. Depending on your programming environment, you might enter SQL directly (for example, to generate reports), embed SQL statements into code written in another language, or use a language-specific API that hides the SQL syntax.
SQL is defined by the ANSI/ISO SQL Standard. 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.
MySQL software is Open Source.
Open Source means that it is possible for anyone to use and modify the software. Anybody can download the MySQL software from the Internet and use it without paying anything. If you wish, you may study the source code and change it to suit your needs. The MySQL software uses the GPL (GNU General Public License), http://www.fsf.org/licenses/, to define what you may and may not do with the software in different situations. If you feel uncomfortable with the GPL or need to embed MySQL code into a commercial application, you can buy a commercially licensed version from us. See the MySQL Licensing Overview for more information (http://www.mysql.com/company/legal/licensing/).
The MySQL Database Server is very fast, reliable, scalable, and easy to use.
If that is what you are looking for, you should give it a try. MySQL Server can run comfortably on a desktop or laptop, alongside your other applications, web servers, and so on, requiring little or no attention. If you dedicate an entire machine to MySQL, you can adjust the settings to take advantage of all the memory, CPU power, and I/O capacity available. MySQL can also scale up to clusters of machines, networked together.
You can find a performance comparison of MySQL Server with other database managers on our benchmark page. See Section 8.13.2, “The MySQL Benchmark Suite”.
MySQL Server was originally developed to handle large databases much faster than existing solutions and has been successfully used in highly demanding production environments for several years. Although under constant development, MySQL Server today offers a rich and useful set of functions. Its connectivity, speed, and security make MySQL Server highly suited for accessing databases on the Internet.
MySQL Server works in client/server or embedded systems.
The MySQL Database Software is a client/server system that consists of a multi-threaded SQL server that supports different backends, several different client programs and libraries, administrative tools, and a wide range of application programming interfaces (APIs).
We also provide MySQL Server as an embedded multi-threaded library that you can link into your application to get a smaller, faster, easier-to-manage standalone product.
A large amount of contributed MySQL software is available.
MySQL Server has a practical set of features developed in close cooperation with our users. It is very likely that your favorite application or language supports the MySQL Database Server.
The official way to pronounce “MySQL” is “My Ess Que Ell” (not “my sequel”), but we do not mind if you pronounce it as “my sequel” or in some other localized way.
This section describes some of the important characteristics of the MySQL Database Software. In most respects, the roadmap applies to all versions of MySQL. For information about features as they are introduced into MySQL on a series-specific basis, see the “In a Nutshell” section of the appropriate Manual:
MySQL 5.6: MySQL 5.6 in a Nutshell
MySQL 5.5: MySQL 5.5 in a Nutshell
MySQL 5.1: MySQL 5.1 in a Nutshell
MySQL 5.0: MySQL 5.0 in a Nutshell
Written in C and C++.
Tested with a broad range of different compilers.
Works on many different platforms. See http://www.mysql.com/support/supportedplatforms/database.html.
For portability, uses CMake in MySQL 5.5 and up. Previous series use GNU Automake, Autoconf, and Libtool.
Tested with Purify (a commercial memory leakage detector) as well as with Valgrind, a GPL tool (http://developer.kde.org/~sewardj/).
Uses multi-layered server design with independent modules.
Designed to be fully multi-threaded using kernel threads, to easily use multiple CPUs if they are available.
Provides transactional and nontransactional storage engines.
Uses very fast B-tree disk tables (MyISAM)
with index compression.
Designed to make it relatively easy to add other storage engines. This is useful if you want to provide an SQL interface for an in-house database.
Uses a very fast thread-based memory allocation system.
Executes very fast joins using an optimized nested-loop join.
Implements in-memory hash tables, which are used as temporary tables.
Implements SQL functions using a highly optimized class library that should be as fast as possible. Usually there is no memory allocation at all after query initialization.
Provides the server as a separate program for use in a client/server networked environment, and as a library that can be embedded (linked) into standalone applications. Such applications can be used in isolation or in environments where no network is available.
Full operator and function support in the
SELECT list and
WHERE clause of queries. For example:
mysql>SELECT CONCAT(first_name, ' ', last_name)->FROM citizen->WHERE income/dependents > 10000 AND age > 30;
Full support for SQL GROUP BY and
ORDER BY clauses. Support for group
functions (COUNT(),
AVG(),
STD(),
SUM(),
MAX(),
MIN(), and
GROUP_CONCAT()).
Support for LEFT OUTER JOIN and
RIGHT OUTER JOIN with both standard SQL and
ODBC syntax.
Support for aliases on tables and columns as required by standard SQL.
Support for DELETE,
INSERT,
REPLACE, and
UPDATE to return the number of
rows that were changed (affected), or to return the number of
rows matched instead by setting a flag when connecting to the
server.
Support for MySQL-specific SHOW
statements that retrieve information about databases, storage
engines, tables, and indexes. MySQL 5.0 adds support for the
INFORMATION_SCHEMA database, implemented
according to standard SQL.
An EXPLAIN statement to show
how the optimizer resolves a query.
Independence of function names from table or column names. For
example, ABS is a valid column name. The
only restriction is that for a function call, no spaces are
permitted between the function name and the
“(” that follows it. See
Section 9.3, “Keywords and Reserved Words”.
You can refer to tables from different databases in the same statement.
A privilege and password system that is very flexible and secure, and that enables host-based verification.
Password security by encryption of all password traffic when you connect to a server.
Support for large databases. We use MySQL Server with databases that contain 50 million records. We also know of users who use MySQL Server with 200,000 tables and about 5,000,000,000 rows.
Support for up to 64 indexes per table (32 before MySQL
4.1.2). Each index may consist of 1 to 16 columns or parts of
columns. The maximum index width is 767 bytes for
InnoDB tables, or 1000 for
MyISAM; before MySQL 4.1.2, the limit is
500 bytes. An index may use a prefix of a column for
CHAR,
VARCHAR,
BLOB, or
TEXT column types.
Clients can connect to MySQL Server using several protocols:
Clients can connect using TCP/IP sockets on any platform.
On Windows systems in the NT family (NT, 2000, XP, 2003,
or Vista), clients can connect using named pipes if the
server is started with the
--enable-named-pipe option.
In MySQL 4.1 and higher, Windows servers also support
shared-memory connections if started with the
--shared-memory option.
Clients can connect through shared memory by using the
--protocol=memory option.
On Unix systems, clients can connect using Unix domain socket files.
MySQL client programs can be written in many languages. A client library written in C is available for clients written in C or C++, or for any language that provides C bindings.
APIs for C, C++, Eiffel, Java, Perl, PHP, Python, Ruby, and Tcl are available, enabling MySQL clients to be written in many languages. See Chapter 23, Connectors and APIs.
The Connector/ODBC (MyODBC) interface provides MySQL support for client programs that use ODBC (Open Database Connectivity) connections. For example, you can use MS Access to connect to your MySQL server. Clients can be run on Windows or Unix. Connector/ODBC source is available. All ODBC 2.5 functions are supported, as are many others. See MySQL Connector/ODBC Developer Guide.
The Connector/J interface provides MySQL support for Java client programs that use JDBC connections. Clients can be run on Windows or Unix. Connector/J source is available. See MySQL Connector/J Developer Guide.
MySQL Connector/Net enables developers to easily create .NET applications that require secure, high-performance data connectivity with MySQL. It implements the required ADO.NET interfaces and integrates into ADO.NET aware tools. Developers can build applications using their choice of .NET languages. MySQL Connector/Net is a fully managed ADO.NET driver written in 100% pure C#. See MySQL Connector/Net Developer Guide.
The server can provide error messages to clients in many languages. See Section 10.2, “Setting the Error Message Language”.
Full support for several different character sets, including
latin1 (cp1252), german,
big5, ujis, and more.
For example, the Scandinavian characters
“å”,
“ä” and
“ö” are permitted in table
and column names. Unicode support is available as of MySQL
4.1.
All data is saved in the chosen character set.
Sorting and comparisons are done according to the chosen
character set and collation (using latin1
and Swedish collation by default). It is possible to change
this when the MySQL server is started. To see an example of
very advanced sorting, look at the Czech sorting code. MySQL
Server supports many different character sets that can be
specified at compile time and runtime.
As of MySQL 4.1, the server time zone can be changed dynamically, and individual clients can specify their own time zone. Section 10.6, “MySQL Server Time Zone Support”.
MySQL includes several client and utility programs. These include both command-line programs such as mysqldump and mysqladmin, and graphical programs such as MySQL Workbench.
MySQL Server has built-in support for SQL statements to check,
optimize, and repair tables. These statements are available
from the command line through the
mysqlcheck client. MySQL also includes
myisamchk, a very fast command-line utility
for performing these operations on MyISAM
tables. See Chapter 4, MySQL Programs.
MySQL programs can be invoked with the --help
or -? option to obtain online assistance.
We started out with the intention of using the
mSQL database system 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 enable third-party code that was written for use with
mSQL to be ported easily for use with MySQL.
MySQL is named after co-founder Monty Widenius's daughter, My.
The name of the MySQL Dolphin (our logo) is “Sakila,” which was chosen 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 feminine 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.
This section summarizes what has been added to, deprecated in, and removed from MySQL 5.5.
The following features have been added to MySQL 5.5:
MySQL Enterprise Thread Pool. The default thread-handling model in MySQL Server executes statements using one thread per client connection. As more clients connect to the server and execute statements, overall performance degrades. As of MySQL 5.5.16, MySQL Enterprise Edition distributions include a thread pool plugin that provides an alternative thread-handling model designed to reduce overhead and improve performance. The plugin implements a thread pool that increases server performance by efficiently managing statement execution threads for large numbers of client connections. For more information, see Section 8.12.7, “The Thread Pool Plugin”.
MySQL Enterprise Audit.
MySQL Enterprise Edition now includes MySQL Enterprise
Audit, implemented using a server plugin named
audit_log. MySQL Enterprise Audit uses
the open MySQL Audit API to enable standard, policy-based
monitoring and logging of connection and query activity
executed on specific MySQL servers. Designed to meet the
Oracle audit specification, MySQL Enterprise Audit provides
an out of box, easy to use auditing and compliance solution
for applications that are governed by both internal and
external regulatory guidelines. When installed, the audit
plugin enables MySQL Server to produce a log file containing
an audit record of server activity. The log contents include
when clients connect and disconnect, and what actions they
perform while connected, such as which databases and tables
they access. For more information, see
Section 6.3.12, “MySQL Enterprise Audit Log Plugin”.
Pluggable authentication.
MySQL authentication supports two new capabilities,
pluggable authentication and proxy users. With pluggable
authentication, the server can use plugins to authenticate
incoming client connections, and clients can load an
authentication plugin that interacts properly with the
corresponding server plugin. This capability enables clients
to connect to the MySQL server with credentials that are
appropriate for authentication methods other than the
built-in MySQL authentication based on native MySQL
passwords stored in the mysql.user table.
For example, plugins can be created to use external
authentication methods such as LDAP, Kerberos, PAM, or
Windows login IDs. Proxy user capability enables a client
who connects and authenticates as one user to be treated,
for purposes of access control while connected, as having
the privileges of a different user. In effect, one user
impersonates another. Proxy capability depends on pluggable
authentication because it is based on having an
authentication plugin return to the server the user name
that the connecting user impersonates. See
Section 6.3.6, “Pluggable Authentication”, and
Section 6.3.8, “Proxy Users”.
As of MySQL 5.5.16, MySQL Enterprise Edition includes two plugins that enable MySQL Server to use external authentication methods to authenticate MySQL users:
PAM (Pluggable Authentication Modules) enables a system to access various kinds of authentication methods through a standard interface. A PAM authentication plugin enables MySQL Server to use PAM to authenticate MySQL users.
Distributions of MySQL for Windows include an authentication plugin that enables MySQL Server to use native Windows services to authenticate client connections. Users who have logged in to Windows can connect from MySQL client programs to the server based on the information in their environment without specifying an additional password.
These authentication plugins enable MySQL Server to accept connections from users defined outside the MySQL grant tables. They also support the MySQL proxy-user capability. Each plugin can return to MySQL a user name different from the login user, which means that the plugin can return the MySQL user that defines the privileges the externally authenticated user should have.
For more information, see Section 6.3.7.3, “The PAM Authentication Plugin”, and Section 6.3.7.4, “The Windows Native Authentication Plugin”.
Multi-core scalability.
Scalability on multi-core CPUs is improved. The trend in
hardware development now is toward more cores rather than
continued increases in CPU clock speeds, which renders
“wait until CPUs get faster” a nonviable means
of improving database performance. Instead, it is necessary
to make better use of multiple cores to maximally exploit
the processing cycles they make available. MySQL
5.5 takes advantage of features of SMP systems
and tries to eliminate bottlenecks in MySQL architecture
that hinder full use of multiple cores. The focus has been
on InnoDB, especially locking
and memory management. See
Section 1.4.1, “Scalability Improvements”.
InnoDB I/O subsystem.
InnoDB I/O subsystem changes
enable more effective use of available I/O capacity. See
Section 1.4.2, “InnoDB I/O Subsystem Changes”.
Diagnostic improvements.
There is better access to execution and performance
information. Diagnostic improvements include Performance
Schema (a feature for monitoring MySQL Server execution at a
low level), DTrace probes, expanded
SHOW ENGINE
INNODB STATUS output, Debug Sync, and a new status
variable. See Section 1.4.3, “Diagnostic and Monitoring Capabilities”.
Solaris. Several modifications improve operation of MySQL Server on Solaris. See Section 1.4.4, “Enhanced Solaris Support”.
Default storage engine.
The default storage engine for new tables is
InnoDB rather than
MyISAM. See
Section 14.1.2, “InnoDB as the Default MySQL Storage Engine”.
MySQL Cluster.
MySQL Cluster is released as a separate product, with new
development for version 7.2 of the
NDB storage engine being based
on MySQL 5.5. Clustering support is not available in
mainline MySQL Server 5.5 releases. For more information
about MySQL Cluster NDB 7.2, see
Chapter 18, MySQL Cluster NDB 7.2.
MySQL Cluster releases are identified by a 3-part NDB version number. Currently, MySQL Cluster NDB 7.1 is the most recent GA release series. MySQL Cluster NDB 6.3 and MySQL Cluster NDB 7.0 are also still available. These versions of MySQL Cluster are based on MySQL Server 5.1 and documented in the MySQL 5.1 Manual. See MySQL Cluster NDB 6.1 - 7.1.
Semisynchronous replication. A commit performed on the master side blocks before returning to the session that performed the transaction until at least one slave acknowledges that it has received and logged the events for the transaction. Semisynchronous replication is implemented through an optional plugin component. See Section 17.3.8, “Semisynchronous Replication”
Unicode.
Support for supplementary Unicode characters; that is,
characters outside the Basic Multilingual Plane (BMP). These
new Unicode character sets include supplementary characters:
utf16, utf32, and
utf8mb4. See
Section 10.1.10, “Unicode Support”.
Partitioning. Enhancements to table partitioning:
Two new types of user-defined partitioning are supported:
RANGE COLUMNS partitioning is an
extension to RANGE partitioning;
LIST COLUMNS partitioning is an
extension to LIST partitioning. Each of
these extensions provides two enhancements to MySQL
partitioning capabilities:
It is possible to define partitioning ranges or lists
based on DATE,
DATETIME, or string
values (such as CHAR or
VARCHAR).
You can also define ranges or lists based on multiple
column values when partitioning tables by
RANGE COLUMNS or LIST
COLUMNS, respectively. Such a range or list
may refer to up to 16 columns.
For tables defined using these partitioning types,
partition pruning can now optimize queries with
WHERE conditions that use multiple
comparisons between (different) column values and
constants, such as a = 10 AND b >
5 or a < "2005-11-25" AND b = 10
AND c = 50.
See Section 19.2.1, “RANGE Partitioning”, and Section 19.2.2, “LIST Partitioning”.
It is now possible to delete all rows from one or more
partitions of a partitioned table using the
ALTER TABLE
... TRUNCATE PARTITION statement. Executing the
statement deletes rows without affecting the structure of
the table. The partitions named in the TRUNCATE
PARTITION clause do not have to be contiguous.
Key caches are now supported for indexes on partitioned
MyISAM tables, using the
CACHE INDEX and
LOAD INDEX
INTO CACHE statements. In addition, a key cache
can be defined for and loaded with indexes from an entire
partitioned table, or for one or more partitions. In the
latter case, the partitions are not required to be
contiguous.
The new TO_SECONDS()
function converts a date or datetime expression to a
number of seconds since the year 0. This is a
general-purpose function, but is useful for partitioning.
You may use it in partitioning expressions, and partition
pruning is supported for tables defined using such
expressions.
SIGNAL and RESIGNAL.
Support for the SQL standard
SIGNAL and
RESIGNAL statements. See
Section 13.6.7, “Condition Handling”.
Metadata locking. The server now prevents DDL statements from compromising transaction serializibility by using a new class of locks called metadata locks. See Section 8.11.4, “Metadata Locking”.
IPv6 support. MySQL Server can accept TCP/IP connections from clients connecting over IPv6. See Section 5.1.9, “IPv6 Support”.
XML.
Enhancements to XML functionality, including a new
LOAD XML
INFILE statement. See Section 13.2.7, “LOAD XML Syntax”.
Build configuration. MySQL releases are now built using CMake rather than the GNU autotools. Accordingly, the instructions for installing MySQL from source have been updated to discuss how to build MySQL using CMake. See Section 2.9, “Installing MySQL from Source”.
The build process is now similar enough on all platforms, including Windows, that there are no longer sections dedicated to notes for specific platforms.
The following features are deprecated in MySQL 5.5 and may be or will be removed in a future series. Where alternatives are shown, applications should be updated to use them.
Relying on implicit GROUP BY sorting in
MySQL 5.5 is deprecated. To achieve a specific
sort order of grouped results, it is preferable to use an
explicit ORDER BY clause. GROUP
BY sorting is a MySQL extension that may change in a
future release; for example, to make it possible for the
optimizer to order groupings in whatever manner it deems most
efficient and to avoid the sorting overhead.
The YEAR(2) data type.
YEAR(2) columns in existing tables are
treated as before, but YEAR(2) in new or
altered tables are converted to YEAR(4).
For more information, see
Section 11.3.4, “YEAR(2) Limitations and Migrating to YEAR(4)”.
The SHOW AUTHORS and SHOW
CONTRIBUTORS statements.
The --ignore-builtin-innodb server option.
It does nothing and has no effect.
The --language server option.
Use the lc_messages_dir and
lc_messages sytem variables
instead.
The ALWAYS value for the
--base64-output option for
mysqlbinlog.
The --config-file option
for mysqld_multi. Use
--defaults-extra-file instead.
Use of unambigious option prefixes. If an unambiguous prefix is given, a warning occurs to provide feedback. Option prefixes are no longer supported in MySQL 5.7; only full options are accepted.
The engine_condition_pushdown
system variable. Use the
engine_condition_pushdown flag of the
optimizer_switch variable
instead.
The timed_mutexes system
variable. It does nothing and has no effect.
The storage_engine system
variable. Use
default_storage_engine
instead.
Use of the data directory as the location for
my.cnf.
The following constructs are obsolete and have been removed in MySQL 5.5. Where alternatives are shown, applications should be updated to use them.
The language system variable (use
lc_messages_dir and
lc_messages).
The log_bin_trust_routine_creators system
variable (use
log_bin_trust_function_creators).
The myisam_max_extra_sort_file_size system
variable.
The record_buffer system variable (use
read_buffer_size).
The sql_log_update system variable.
The Innodb_buffer_pool_read_ahead_rnd and
Innodb_buffer_pool_read_ahead_seq status
variables (use
Innodb_buffer_pool_read_ahead
and
Innodb_buffer_pool_read_ahead_evicted).
The table_lock_wait_timeout system
variable.
The table_type system variable (use
default_storage_engine).
The FRAC_SECOND modifier for the
TIMESTAMPADD() function (use
MICROSECOND).
The TYPE table option to specify the
storage engine for CREATE TABLE
or ALTER TABLE (use
ENGINE).
The SHOW TABLE TYPES SQL statement (use
SHOW ENGINES).
The SHOW INNODB STATUS and SHOW
MUTEX STATUS SQL statements (use
SHOW ENGINE
INNODB STATUS and
SHOW ENGINE
INNODB MUTEX).
The SHOW PLUGIN SQL statement (use
SHOW PLUGINS).
The LOAD TABLE ... FROM MASTER and
LOAD DATA FROM MASTER SQL statements (use
mysqldump or
mysqlhotcopy to dump tables and
mysql to reload dump files).
The BACKUP TABLE and RESTORE
TABLE SQL statements (use
mysqldump or
mysqlhotcopy to dump tables and
mysql to reload dump files).
TIMESTAMP(
data type: The ability to specify a display width of
N)N (use without
N).
The --default-character-set and
--default-collation server options (use
--character-set-server and
--collation-server).
The --default-table-type server option (use
--default-storage-engine).
The --delay-key-write-for-all-tables server
option (use
--delay-key-write=ALL).
The --enable-locking and
--skip-locking server options (use
--external-locking and
--skip-external-locking).
The --log-bin-trust-routine-creators server
option (use
--log-bin-trust-function-creators).
The --log-long-format server option.
The --log-update server option.
The --master-
server options to set replication parameters (use the
xxxCHANGE MASTER TO statement
instead): --master-host,
--master-user,
--master-password,
--master-port,
--master-connect-retry,
--master-ssl,
--master-ssl-ca,
--master-ssl-capath,
--master-ssl-cert,
--master-ssl-cipher,
--master-ssl-key.
The --safe-show-database server option.
The --skip-symlink and
--use-symbolic-links server options (use
--skip-symbolic-links
and --symbolic-links).
The --sql-bin-update-same server option.
The --warnings server option (use
--log-warnings).
The --no-named-commands option for
mysql (use
--skip-named-commands).
The --no-pager option for
mysql (use --skip-pager).
The --no-tee option for
mysql (use --skip-tee).
The --position option for
mysqlbinlog (use
--start-position).
The --all option for
mysqldump (use
--create-options).
The --first-slave option for
mysqldump (use
--lock-all-tables).
The --config-file option for
mysqld_multi (use
--defaults-extra-file).
The
--set-variable=
and var_name=value-O
general-purpose options for setting program variables (use
var_name=value--).
var_name=value
The --with-pstack option for
configure and the
--enable-pstack option for
mysqld.
MySQL 5.5 modifications improve performance on SMP
systems to increase scalability on multi-core systems. The
changes affect InnoDB locking and
memory management.
MySQL 5.5 incorporates changes in
InnoDB that improve the performance
of RW-locks by using atomic CPU instructions (on platforms where
they are available), rather than less scalable mutexes. It is
also possible for InnoDB memory
allocation to be disabled and replaced by the normal
malloc library, or by a different library
that implements malloc such as
tcmalloc on Linux or
mtalloc on Solaris.
The reimplementation of RW-locks requires atomic instructions. A
status variable,
Innodb_have_atomic_builtins,
shows whether the server was built with atomic instructions.
MySQL 5.5 changes to the
InnoDB I/O subsystem enable more
effective use of available I/O capacity. The changes also
provide more control over configuration of the I/O subsystem.
Background I/O Threads
InnoDB uses background threads to
perform I/O for several kinds of activities, two of which are
prefetching disk blocks and flushing dirty pages. Previously,
InnoDB used only one thread each to
perform these activities, but that can underutilize server
capacity. MySQL 5.5 enables use of multiple
background read and write threads, making it possible to read
and write pages faster.
The patch makes the number of background I/O threads
configurable using system variables:
innodb_read_io_threads controls
the number of threads to use for read prefetch requests.
innodb_write_io_threads
controls the number of threads to use for writing dirty pages
from the buffer cache to disk. The default for both variables is
4.
The ability to increase the number of I/O threads can benefit
systems that use multiple disks for
InnoDB. However, the type of I/O
being done should be considered. On systems that use buffered
writes rather than direct writes, increasing the write thread
count higher than 1 might yield little benefit because writes
will be quick already.
Adjustable I/O Rate
Previously, the number of input/output operations per second
(IOPS) that InnoDB will perform was
a compile-time parameter. The rate was chosen to prevent
background I/O from exhausting server capacity and the
compiled-in value of 100 reflected an assumption that the server
can perform 100 IOPS. However, many modern systems can exceed
this, so the value is low and unnecessarily restricts I/O
utilization.
MySQL 5.5 exposes this I/O rate parameter as a
system variable,
innodb_io_capacity. This
variable can be set at server startup, which enables higher
values to be selected for systems capable of higher I/O rates.
Having a higher I/O rate can help the server handle a higher
rate of row changes because it may be able to increase
dirty-page flushing, deleted-row removal, and application of
changes in the change buffer. The default value of
innodb_io_capacity is 200. In
general, you can increase the value as a function of the number
of drives used for InnoDB I/O.
The ability to raise the I/O limit should be especially
beneficial on platforms that support many IOPS. For example,
systems that use multiple disks or solid-state disks for
InnoDB are likely to benefit from
the ability to control this parameter.
MySQL 5.5 provides improved access to execution and
performance information. Diagnostic improvements include
Performance Schema, Dtrace probes, expanded
SHOW ENGINE INNODB
STATUS output, Debug Sync, and a new status variable.
Performance Schema
Performance Schema is a feature for monitoring MySQL Server execution at a low level. See Chapter 22, MySQL Performance Schema.
DTrace Support
The DTrace probes work on Solaris, OS X, and FreeBSD. For information on using DTrace in MySQL, see Section 5.4, “Tracing mysqld Using DTrace”.
Enhanced
SHOW ENGINE INNODB
STATUS Output
The output from
SHOW ENGINE INNODB
STATUS includes more information due to changes made
for InnoDB Plugin. A description of revisions
to statement output follows.
A new BACKGROUND THREAD section has
srv_master_thread lines that show work done
by the main background thread.
---------- BACKGROUND THREAD ---------- srv_master_thread loops: 53 1_second, 44 sleeps, 5 10_second, 7 background, 7 flush srv_master_thread log flush and writes: 48
The SEMAPHORES section includes a line to
show the number of spinlock rounds per OS wait for a mutex.
---------- SEMAPHORES ---------- ... Spin rounds per wait: 0.00 mutex, 20.00 RW-shared, 0.00 RW-excl
Debug Sync
The Debug Sync facility provides synchronization points for debugging, see MySQL Internals: Test Synchronization.
New Status Variable
The
Innodb_have_atomic_builtins
status variable provides information about availability of
atomic instructions; see Section 1.4.1, “Scalability Improvements”.
MySQL 5.5 incorporates several modifications for improved operation of MySQL Server on Solaris:
DTrace support for execution monitoring. See Section 1.4.3, “Diagnostic and Monitoring Capabilities”.
Atomic instructions, which are needed for the improvements to RW-locking described in Section 1.4.1, “Scalability Improvements”. Atomic instructions now are supported for Sun Studio on SPARC and x86 platforms. This extends their previous availability (supported for gcc 4.1 and up on all platforms).
The SMP improvements described in Section 1.4.1, “Scalability Improvements”, were originally intended for x86 platforms. In MySQL 5.5, these also work on SPARC platforms. Also, Solaris optimizations have been implemented.
Large page support is enhanced for recent SPARC platforms.
Standard use of large pages in MySQL attempts to use the
largest size supported, up to 4MB. Under Solaris, a
“super large pages” feature enables uses of
pages up to 256MB. This feature can be enabled or disabled
by using the
--super-large-pages or
--skip-super-large-pages
option.
Inline handling for InnoDB and
processor instruction prefetching support, previously not
enabled for builds created using Sun Studio, now are
supported for that build environment.
This section lists sources of additional information that you may find helpful, such as the MySQL mailing lists and user forums, and Internet Relay Chat.
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 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/. For most of them, you can select the regular version of the list where you get individual messages, or a digest version where you get one large message per day.
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.
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
The list for announcements of new versions of MySQL and related programs. This is a low-volume list to which all MySQL users should subscribe.
mysql
The main list for general MySQL discussion. Please note that some topics are better discussed on the more-specialized lists. If you post to the wrong list, you may not get an answer.
bugs
The list for people who want to stay informed about issues reported since the last release of MySQL or who want to be actively involved in the process of bug hunting and fixing. See Section 1.6, “How to Report Bugs or Problems”.
internals
The list for people who work on the MySQL code. This is also the forum for discussions on MySQL development and for posting patches.
mysqldoc
The list for people who work on the MySQL documentation.
benchmarks
The list for anyone interested in performance issues. Discussions concentrate on database performance (not limited to MySQL), but also include broader categories such as performance of the kernel, file system, disk system, and so on.
packagers
The list for discussions on packaging and distributing MySQL. This is the forum used by distribution maintainers to exchange ideas on packaging MySQL and on ensuring that MySQL looks and feels as similar as possible on all supported platforms and operating systems.
java
The list for discussions about the MySQL server and Java. It is mostly used to discuss JDBC drivers such as MySQL Connector/J.
win32
The list for all topics concerning the MySQL software on Microsoft operating systems, such as Windows 9x, Me, NT, 2000, XP, and 2003.
myodbc
The list for all topics concerning connecting to the MySQL server with ODBC.
gui-tools
The list for all topics concerning MySQL graphical user interface tools such as MySQL Workbench.
cluster
The list for discussion of MySQL Cluster.
dotnet
The list for discussion of the MySQL server and the .NET platform. It is mostly related to MySQL Connector/Net.
plusplus
The list for all topics concerning programming with the C++ API for MySQL.
perl
The list for all topics concerning Perl support for MySQL with
DBD::mysql.
If you're unable to get an answer to your questions from a MySQL mailing list or forum, one option is to purchase support from Oracle. This puts you in direct contact with MySQL developers.
The following MySQL mailing lists are in languages other than English. These lists are not operated by Oracle.
<mysql-france-subscribe@yahoogroups.com>
A French mailing list.
A Korean mailing list. To subscribe, email subscribe
mysql your@email.address to this list.
<mysql-de-request@lists.4t2.com>
A German mailing list. To subscribe, email 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>
A Portuguese mailing list. To subscribe, email
subscribe mysql-br your@email.address to
this list.
A Spanish mailing list. To subscribe, email subscribe
mysql your@email.address to this list.
Please do not post mail messages from your browser with HTML mode turned on. Many users do not read mail with a browser.
When you answer a question sent to a mailing list, if you consider your answer to have broad interest, you may want to post it to the 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. Do not feel obliged to quote the entire original message.
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.
The forums at http://forums.mysql.com are an important community resource. Many forums are available, grouped into these general categories:
Migration
MySQL Usage
MySQL Connectors
Programming Languages
Tools
3rd-Party Applications
Storage Engines
MySQL Technology
SQL Standards
Business
In addition to the various MySQL mailing lists and forums, you can find experienced community people on Internet Relay Chat (IRC). These are the best networks/channels currently known to us:
freenode (see http://www.freenode.net/ for servers)
#mysql is primarily for MySQL questions,
but other database and general SQL questions are welcome.
Questions about PHP, Perl, or C in combination with MySQL are
also common.
#workbench is primarily for MySQL Workbench
related questions and thoughts, and it is also a good place to
meet the MySQL Workbench developers.
If you are looking for IRC client software to connect to an IRC
network, take a look at xChat
(http://www.xchat.org/). X-Chat (GPL licensed) is
available for Unix as well as for Windows platforms (a free
Windows build of X-Chat is available at
http://www.silverex.org/download/).
Oracle offers technical support in the form of MySQL Enterprise. For organizations that rely on the MySQL DBMS for business-critical production applications, MySQL Enterprise is a commercial subscription offering which includes:
MySQL Enterprise Server
MySQL Enterprise Monitor
Monthly Rapid Updates and Quarterly Service Packs
MySQL Knowledge Base
24x7 Technical and Consultative Support
MySQL Enterprise is available in multiple tiers, giving you the flexibility to choose the level of service that best matches your needs. For more information, see MySQL Enterprise.
Before posting a bug report about a problem, please try to verify that it is a bug and that it has not been reported already:
Start by searching the MySQL online manual at http://dev.mysql.com/doc/. We try to keep the manual up to date by updating it frequently with solutions to newly found problems. In addition, the release notes accompanying the manual can be particularly useful since it is quite possible that a newer version contains a solution to your problem. The release notes are available at the location just given for the manual.
If you get a parse error for an SQL statement, please check your syntax closely. If you cannot find something wrong with it, it is 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 doesn't cover the syntax that you are using, MySQL Server doesn't support your statement.
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.
For solutions to some common problems, see Section B.5, “Problems and Common Errors”.
Search the bugs database at http://bugs.mysql.com/ to see whether the bug has been reported and fixed.
Search the MySQL mailing list archives at http://lists.mysql.com/. See Section 1.5.1, “MySQL Mailing Lists”.
You can also use http://www.mysql.com/search/ to search all the Web pages (including the manual) that are located at the MySQL Web site.
If you cannot find an answer in the manual, the bugs database, or the mailing list archives, check with your local MySQL expert. If you still cannot find an answer to your question, please use the following guidelines for reporting the bug.
The normal way to report bugs is to visit 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 can enter new reports.
Bugs posted in the bugs database at http://bugs.mysql.com/ that are corrected for a given release are noted in the release notes.
If you find a sensitive security bug in MySQL Server, please let us
know immediately by sending an email message to
<secalert_us@oracle.com>. Exception: Support customers
should report all problems, including security bugs, to Oracle
Support at http://support.oracle.com/.
To discuss problems with other users, you can use one of the MySQL mailing lists. Section 1.5.1, “MySQL Mailing Lists”.
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 helps you write your report correctly so that you do not waste your time doing things that may not help us much or at all. 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 your test case or by running the shell or
Perl script that you include in the bug report. Any bug that we are
able to repeat has a high chance of being fixed in the next MySQL
release.
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 24.4, “Debugging and Porting MySQL”.
Remember that it is possible for us to respond to a report 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 do not matter. A good principle to follow is that 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 that you use, and (b) not fully describing the platform on which the MySQL server is installed (including the platform type and version number). These are highly relevant pieces of information, and in 99 cases out of 100, the bug report is useless without them. Very often we get questions like, “Why doesn't this work for me?” Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has been fixed in newer MySQL versions. Errors often are 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 used. Note that every compiling problem should be regarded as a bug and reported accordingly.
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, it is better that the error message reported exactly matches the one that the program produces. (Even the lettercase should be observed.) It is best to copy and paste the entire error message into your report. You should never try to reproduce the message from memory.
If you have a problem with Connector/ODBC (MyODBC), please try to generate a trace file and send it with your report. See How to Report Connector/ODBC Problems or Bugs.
If your report includes long query output lines from test cases that
you run with the mysql command-line tool, you can
make the output more readable by using the
--vertical option or the
\G statement terminator. The
EXPLAIN SELECT
example later in this section demonstrates the use of
\G.
Please include the following information in your report:
The version number of the MySQL distribution you are using (for
example, MySQL 5.0.19). You can find out which version you are
running by executing mysqladmin version. The
mysqladmin program can be found in the
bin directory under your MySQL installation
directory.
The manufacturer and model of the machine on which you experience the problem.
The operating system name and version. If you work with Windows,
you can usually get the name and version number by
double-clicking your My Computer icon and pulling down the
“Help/About Windows” menu. For most Unix-like
operating systems, you can get this information by executing the
command uname -a.
Sometimes the amount of memory (real and virtual) is relevant. If in doubt, include these values.
If you are using a source distribution of the MySQL software, include the name and version number of the compiler that you used. If you have a binary distribution, include the distribution name.
If the problem occurs during compilation, include the exact error messages and also a few lines of context around the offending code in the file where the error occurs.
If mysqld died, you should also report the statement that crashed mysqld. You can usually get this information by running mysqld with query logging enabled, and then looking in the log after mysqld crashes. See Section 24.4, “Debugging and Porting MySQL”.
If a database table is related to the problem, include the
output from the SHOW CREATE TABLE
statement in the bug report. This is a very easy way to get the
definition of any table in a database. The information helps us
create a situation matching the one that you have experienced.
db_name.tbl_name
The SQL mode in effect when the problem occurred can be
significant, so please report the value of the
sql_mode system variable. For
stored procedure, stored function, and trigger objects, the
relevant sql_mode value is the
one in effect when the object was created. For a stored
procedure or function, the SHOW CREATE
PROCEDURE or SHOW CREATE
FUNCTION statement shows the relevant SQL mode, or you
can query INFORMATION_SCHEMA for the
information:
SELECT ROUTINE_SCHEMA, ROUTINE_NAME, SQL_MODE FROM INFORMATION_SCHEMA.ROUTINES;
For triggers, you can use this statement:
SELECT EVENT_OBJECT_SCHEMA, EVENT_OBJECT_TABLE, TRIGGER_NAME, SQL_MODE FROM INFORMATION_SCHEMA.TRIGGERS;
For performance-related bugs or problems with
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
for each table
that is involved. The more information you provide about your
situation, the more likely it is that someone can help you.
tbl_name
The following is an example of a very good bug report. The
statements are run using the mysql
command-line tool. Note the use of the \G
statement terminator for statements that would otherwise provide
very long output lines that are difficult to read.
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>
If a bug or problem occurs while running mysqld, try to provide an input script that reproduces 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 upload it to be attached to the bug report.
If you cannot provide a script, you should at least include the output from mysqladmin variables extended-status processlist in your report to provide some information on how your system is performing.
If you cannot produce a test case with only a few rows, or if
the test table is too big to be included in the bug report (more
than 10 rows), you should dump your tables using
mysqldump and create a
README file that describes your problem.
Create a compressed archive of your files using
tar and gzip or
zip. After you initiate a bug report for our
bugs database at http://bugs.mysql.com/, click
the Files tab in the bug report for instructions on uploading
the archive to the bugs database.
If you believe that the MySQL server produces a strange result from a statement, include not only the result, but also your opinion of what the result should be, and an explanation describing the basis for your opinion.
When you provide an example of the problem, it is better to use the table names, variable names, and so forth that exist in your actual situation than to come up with new names. The problem could be related to the name of a table or variable. These cases are rare, perhaps, but it is better to be safe than sorry. After all, it should be easier for you to provide an example that uses your actual situation, and it is by all means better for us. If you have data that you do not want to be visible to others in the bug report, you can upload it using the Files tab as previously described. If the information is really top secret and you do not want to show it even to us, go ahead and provide an example using other names, but please regard this as the last choice.
Include all the options given to the relevant programs, if
possible. For example, indicate the options that you use when
you start the 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 key to resolving
problems and are very relevant. It is never a bad idea to
include them. If your problem involves a program written in a
language such as Perl or PHP, please include the language
processor's version number, as well as the version for any
modules that the program uses. For example, if you have a Perl
script that uses the DBI and
DBD::mysql modules, include the version
numbers for Perl, DBI, and
DBD::mysql.
If your question is related to the privilege system, please include the output of mysqladmin reload, and all the error messages you get when trying to connect. When you test your privileges, you should execute mysqladmin reload version and try to connect with the program that gives you trouble.
If you have a patch for a bug, do include it. But do not assume that the patch is all we need, or that we can use it, if you do not provide some necessary information such as test cases showing the bug that your patch fixes. We might find problems with your patch or we might not understand it at all. If so, we cannot use it.
If we cannot verify the exact purpose of the patch, we will not use it. Test cases help us here. Show that the patch handles all the situations that may occur. If we find a borderline case (even a rare one) where the patch will not work, it may be useless.
Guesses about what the bug is, why it occurs, or what it depends on are usually wrong. Even the MySQL team cannot guess such things without first using a debugger to determine the real cause of a bug.
Indicate in your bug report that you have checked the reference manual and mail archive so that others know you have tried to solve the problem yourself.
If your data appears corrupt or you get errors when you access a
particular table, first check your tables with
CHECK TABLE. If that statement
reports any errors:
The InnoDB crash recovery mechanism
handles cleanup when the server is restarted after being
killed, so in typical operation there is no need to
“repair” tables. If you encounter an error with
InnoDB tables, restart the server and see
whether the problem persists, or whether the error affected
only cached data in memory. If data is corrupted on disk,
consider restarting with the
innodb_force_recovery
option enabled so that you can dump the affected tables.
For non-transactional tables, try to repair them with
REPAIR TABLE or with
myisamchk. See
Chapter 5, MySQL Server Administration.
If you are running Windows, please verify the value of
lower_case_table_names using
the SHOW VARIABLES LIKE
'lower_case_table_names' statement. This variable
affects how the server handles lettercase of database and table
names. Its effect for a given value should be as described in
Section 9.2.2, “Identifier Case Sensitivity”.
If you often get corrupted tables, you should try to find out
when and why this happens. In this case, the error log in the
MySQL data directory may contain some information about what
happened. (This is the file with the .err
suffix in the name.) See Section 5.2.2, “The Error Log”. Please
include any relevant information from this file in your bug
report. Normally 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 is much easier for us to
provide you with a fix for the problem. See
Section B.5.1, “How to Determine What Is Causing a Problem”.
If possible, download and install the most recent version of MySQL Server and check whether it solves your problem. All versions of the MySQL software are thoroughly tested and should work without problems. We believe in making everything as backward-compatible as possible, and you should be able to switch MySQL versions without difficulty. See Section 2.1.1, “Which MySQL Version and Distribution to Install”.
This section describes how MySQL relates to the ANSI/ISO SQL standards. MySQL Server has many extensions to the SQL standard, and here you can find out what they are and how to use them. You can also find information about functionality missing from MySQL Server, and how to work around some of the 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, “SQL:2003” refers to the standard released in 2003, and “SQL:2008” refers to the most recent version of the standard, released in 2008. We use the phrase “the SQL standard” or “standard SQL” to mean the current version of the SQL Standard at any time.
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 is an example
of this strategy. See Section 13.2.4, “HANDLER Syntax”.
We continue to support transactional and nontransactional databases to satisfy both mission-critical 24/7 usage and heavy Web or logging usage.
MySQL Server was originally designed to work with medium-sized databases (10-100 million rows, or about 100MB per table) on small computer systems. Today MySQL Server handles terabyte-sized 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 real-time support, although MySQL replication capabilities offer significant functionality.
MySQL supports ODBC levels 0 to 3.51.
MySQL supports high-availability database clustering using the
NDBCLUSTER storage engine. See
Chapter 18, MySQL Cluster NDB 7.2.
We are implementing XML functionality beginning in MySQL 5.1, which supports most of the W3C XPath standard. See Section 12.11, “XML Functions”.
The MySQL server can operate in different SQL modes, and can apply
these modes differently for different clients, depending on the
value of the sql_mode system
variable. DBAs can set the global SQL mode to match site server
operating requirements, and each application can set its session
SQL mode to its own requirements.
Modes affect the SQL syntax MySQL supports and the data validation checks it performs. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.
For more information on setting the SQL mode, see Section 5.1.7, “Server SQL Modes”.
To run MySQL Server in ANSI mode, start mysqld
with the --ansi option. Running the
server in ANSI mode is the same as starting it with the following
options:
--transaction-isolation=SERIALIZABLE --sql-mode=ANSI
To achieve the same effect at runtime, execute these two statements:
SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE; SET GLOBAL sql_mode = 'ANSI';
You can see that setting the
sql_mode system variable to
'ANSI' enables all SQL mode options that are
relevant for ANSI mode as follows:
mysql>SET GLOBAL sql_mode='ANSI';mysql>SELECT @@global.sql_mode;-> 'REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ANSI'
Running the server in ANSI mode with
--ansi is not quite the same as
setting the SQL mode to 'ANSI' because the
--ansi option also sets the
transaction isolation level.
See Section 5.1.3, “Server Command Options”.
MySQL Server supports some extensions that you probably will not find in other SQL DBMSs. 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 following form:
/*! MySQL-specific code */
In this case, MySQL Server parses and executes the code within
the comment as it would any other SQL statement, but other SQL
servers will ignore the extensions. For example, MySQL Server
recognizes the STRAIGHT_JOIN keyword in the
following statement, but other servers will not:
SELECT /*! STRAIGHT_JOIN */ col1 FROM table1,table2 WHERE ...
If you add a version number after the
“!” character, the syntax within
the comment is executed only if the MySQL version is greater
than or equal to the specified version number. The
TEMPORARY keyword in the following comment is
executed only by servers from MySQL 3.23.02 or higher:
CREATE /*!32302 TEMPORARY */ TABLE t (a INT);
The following descriptions list MySQL extensions, organized by category.
Organization of data on disk
MySQL Server maps each database to a directory under the MySQL data directory, and maps tables within a database to file names in the database directory. This has a few implications:
Database and table names are case sensitive in MySQL Server on operating systems that have case-sensitive file names (such as most Unix systems). See Section 9.2.2, “Identifier Case Sensitivity”.
You can use standard system commands to back up, rename,
move, delete, and copy tables that are managed by the
MyISAM storage engine. For example,
it is possible to rename a MyISAM
table by renaming the .MYD,
.MYI, and .frm
files to which the table corresponds. (Nevertheless, it
is preferable to use RENAME
TABLE or ALTER TABLE ...
RENAME and let the server rename the files.)
General language syntax
By default, strings can be enclosed by
“"” as well as
“'”. If the
ANSI_QUOTES SQL mode
is enabled, strings can be enclosed only by
“'” and the server
interprets strings enclosed by
“"” as identifiers.
“\” is the escape
character in strings.
In SQL statements, you can access tables from different
databases with the
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.
SQL statement syntax
The ANALYZE TABLE,
CHECK TABLE,
OPTIMIZE TABLE, and
REPAIR TABLE statements.
The CREATE DATABASE,
DROP DATABASE, and
ALTER DATABASE
statements. See Section 13.1.10, “CREATE DATABASE Syntax”,
Section 13.1.21, “DROP DATABASE Syntax”, and
Section 13.1.1, “ALTER DATABASE Syntax”.
The DO statement.
EXPLAIN
SELECT to obtain a description of how tables
are processed by the query optimizer.
The
SET
statement. See Section 13.7.4, “SET Syntax”.
The SHOW statement. See
Section 13.7.5, “SHOW Syntax”. The information produced by many
of the MySQL-specific
SHOW statements can be
obtained in more standard fashion by using
SELECT to query
INFORMATION_SCHEMA. See
Chapter 21, INFORMATION_SCHEMA Tables.
Use of LOAD
DATA INFILE. In many cases, this syntax is
compatible with Oracle's
LOAD DATA
INFILE. See Section 13.2.6, “LOAD DATA INFILE Syntax”.
Use of RENAME TABLE. See
Section 13.1.32, “RENAME TABLE Syntax”.
Use of REPLACE instead of
DELETE plus
INSERT. See
Section 13.2.8, “REPLACE Syntax”.
Use of CHANGE
,
col_nameDROP
, or
col_nameDROP INDEX,
IGNORE or RENAME
in ALTER TABLE
statements. Use of multiple ADD,
ALTER, DROP, or
CHANGE clauses in an
ALTER TABLE statement.
See Section 13.1.7, “ALTER TABLE Syntax”.
Use of index names, indexes on a prefix of a column, and
use of INDEX or
KEY in CREATE
TABLE statements. See
Section 13.1.17, “CREATE TABLE Syntax”.
Use of TEMPORARY or IF NOT
EXISTS with CREATE
TABLE.
Use of IF EXISTS with
DROP TABLE and
DROP DATABASE.
The capability of dropping multiple tables with a single
DROP TABLE statement.
The ORDER BY and
LIMIT clauses of the
UPDATE and
DELETE statements.
INSERT INTO
syntax.
tbl_name
SET col_name = ...
The LOW_PRIORITY clause of the
INSERT,
REPLACE,
DELETE, and
UPDATE statements.
Use of INTO OUTFILE or INTO
DUMPFILE in
SELECT statements. See
Section 13.2.9, “SELECT Syntax”.
Options such as STRAIGHT_JOIN or
SQL_SMALL_RESULT in
SELECT statements.
You don't need to name all selected columns in the
GROUP BY clause. This gives better
performance for some very specific, but quite normal
queries. See
Section 12.17, “Functions and Modifiers for Use with GROUP BY Clauses”.
You can specify ASC and
DESC with GROUP
BY, not just with ORDER BY.
The ability to set variables in a statement with the
:= assignment operator. See
Section 9.4, “User-Defined Variables”.
Data types
Functions and operators
To make it easier for users who migrate from other SQL environments, MySQL Server supports aliases for many functions. For example, all string functions support both standard SQL syntax and ODBC syntax.
MySQL Server understands the
|| 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 is easy to convert use of the
|| operator
to MySQL Server.
Use of COUNT(DISTINCT
where
value_list)value_list has more than one
element.
String comparisons are case-insensitive by default, with
sort ordering determined by the collation of the current
character set, which is latin1
(cp1252 West European) by default. If you don't like
this, you should declare your columns with the
BINARY attribute or use the
BINARY cast, which causes comparisons
to be done using the underlying character code values
rather than a lexical ordering.
The %
operator is a synonym for
MOD(). That is,
N %
MMOD(.
N,M)% is
supported for C programmers and for compatibility with
PostgreSQL.
The =,
<>,
<=,
<,
>=,
>,
<<,
>>,
<=>,
AND,
OR, or
LIKE
operators may be used in expressions in the output
column list (to the left of the FROM)
in SELECT statements. For
example:
mysql> SELECT col1=1 AND col2=2 FROM my_table;
The LAST_INSERT_ID()
function returns the most recent
AUTO_INCREMENT value. See
Section 12.14, “Information Functions”.
LIKE is permitted on
numeric values.
The 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 a variable number of arguments.)
The BIT_COUNT(),
CASE,
ELT(),
FROM_DAYS(),
FORMAT(),
IF(),
PASSWORD(),
ENCRYPT(),
MD5(),
ENCODE(),
DECODE(),
PERIOD_ADD(),
PERIOD_DIFF(),
TO_DAYS(), and
WEEKDAY() functions.
Use of TRIM() to trim
substrings. Standard SQL supports removal of single
characters only.
The GROUP BY functions
STD(),
BIT_OR(),
BIT_AND(),
BIT_XOR(), and
GROUP_CONCAT(). See
Section 12.17, “Functions and Modifiers for Use with GROUP BY Clauses”.
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:
There are several differences between the MySQL and standard
SQL privilege systems. For example, in MySQL, privileges for
a table are not automatically revoked when you delete a
table. You must explicitly issue a
REVOKE statement to revoke
privileges for a table. For more information, see
Section 13.7.1.5, “REVOKE Syntax”.
The CAST() function does not
support cast to REAL or
BIGINT. See
Section 12.10, “Cast Functions and Operators”.
MySQL Server doesn't support the SELECT ... INTO
TABLE Sybase SQL extension. Instead, MySQL Server
supports the
INSERT INTO ...
SELECT standard SQL syntax, which is basically the
same thing. See Section 13.2.5.1, “INSERT ... SELECT Syntax”. For example:
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.
You can use SELECT ...
INTO with user-defined variables. The same syntax
can also be used inside stored routines using cursors and
local variables. See Section 13.2.9.1, “SELECT ... INTO Syntax”.
If you access a column from the table to be updated in an
expression, UPDATE uses the
current value of the column. The second assignment in the
following statement sets col2 to the
current (updated) col1 value, not the
original col1 value. The result is that
col1 and col2 have the
same value. This behavior differs from standard SQL.
UPDATE t1 SET col1 = col1 + 1, col2 = col1;
MySQL's implementation of foreign keys differs from the SQL standard in the following key respects:
If there are several rows in the parent table that have
the same referenced key value,
InnoDB acts in foreign key
checks as if the other parent rows with the same key value
do not exist. For example, if you have defined a
RESTRICT type constraint, and there is
a child row with several parent rows,
InnoDB does not permit the deletion of
any of those parent rows.
InnoDB performs cascading operations
through a depth-first algorithm, based on records in the
indexes corresponding to the foreign key constraints.
A FOREIGN KEY constraint that
references a non-UNIQUE key is not
standard SQL but rather an
InnoDB extension.
If ON UPDATE CASCADE or ON
UPDATE SET NULL recurses to update the
same table it has previously updated
during the same cascade, it acts like
RESTRICT. This means that you cannot
use self-referential ON UPDATE CASCADE
or ON UPDATE SET NULL operations. This
is to prevent infinite loops resulting from cascaded
updates. A self-referential ON DELETE SET
NULL, on the other hand, is possible, as is a
self-referential ON DELETE CASCADE.
Cascading operations may not be nested more than 15 levels
deep.
In an SQL statement that inserts, deletes, or updates many
rows, foreign key constraints (like unique constraints)
are checked row-by-row. When performing foreign key
checks, InnoDB sets shared
row-level locks on child or parent records that it must
examine. MySQL checks foreign key constraints immediately;
the check is not deferred to transaction commit. According
to the SQL standard, the default behavior should be
deferred checking. That is, constraints are only checked
after the entire SQL statement has
been processed. This means that it is not possible to
delete a row that refers to itself using a foreign key.
For information about how the
InnoDB storage engine handles
foreign keys, see
Section 14.8.6, “InnoDB and FOREIGN KEY Constraints”.
Standard SQL uses the C syntax /* this is a comment
*/ for comments, and MySQL Server supports this
syntax as well. MySQL also support extensions to this syntax
that enable MySQL-specific SQL to be embedded in the comment,
as described in Section 9.6, “Comment Syntax”.
Standard SQL uses “--” as a
start-comment sequence. MySQL Server uses
“#” as the start comment
character. MySQL Server 3.23.3 and up also supports a variant
of the “--” comment style.
That is, the “--”
start-comment sequence must be followed by a space (or by a
control character such as a newline). The space is required to
prevent problems with automatically generated SQL queries that
use constructs such as the following, where we automatically
insert the value of the payment for
payment:
UPDATE account SET credit=credit-payment
Consider about what happens if payment has
a negative value such as -1:
UPDATE account SET credit=credit--1
credit--1 is a valid expression in SQL, but
“--” 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 permitting comments to start with
“--” can have serious
consequences.
Using our implementation requires a space following the
“--” for it to be recognized
as a start-comment sequence in MySQL Server 3.23.3 and newer.
Therefore, credit--1 is safe to use.
Another safe feature is that the mysql
command-line client ignores 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 script in a text file that contains
“--” comments, you should use
the replace utility as follows to convert
the comments to use “#”
characters before executing the script:
shell>replace " --" " #" < text-file-with-funny-comments.sql \| mysqldb_name
That is safer than executing the script in the usual way:
shell> mysql db_name < text-file-with-funny-comments.sql
You can also edit the script 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
See Section 4.8.2, “replace — A String-Replacement Utility”.
MySQL enables you to work both with transactional tables that permit rollback and with nontransactional tables that do not. Because of this, constraint handling is a bit different in MySQL than in other DBMSs. We must handle the case when you have inserted or updated a lot of rows in a nontransactional table for which changes cannot be rolled back when an error occurs.
The basic philosophy is that MySQL Server tries to produce an error for anything that it can detect while parsing a statement to be executed, and tries to recover from any errors that occur while executing the statement. We do this in most cases, but not yet for all.
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. By default, the server follows the latter course. This means, for example, that the server may coerce invalid values to the closest valid values.
Several SQL mode options are available to provide greater control over handling of bad data values and whether to continue statement execution or abort when errors occur. Using these options, you can configure MySQL Server to act in a more traditional fashion that is like other DBMSs that reject improper input. The SQL mode can be set globally at server startup to affect all clients. Individual clients can set the SQL mode at runtime, which enables each client to select the behavior most appropriate for its requirements. See Section 5.1.7, “Server SQL Modes”.
The following sections describe how MySQL Server handles different types of constraints.
Normally, errors occurs for data-change statements (such as
INSERT or
UPDATE) that would violate
primary-key, unique-key, or foreign-key constraints. If you
are using a transactional storage engine such as
InnoDB, MySQL automatically rolls back the
statement. If you are using a nontransactional storage engine,
MySQL stops processing the statement at the row for which the
error occurred and leaves any remaining rows unprocessed.
MySQL supports an IGNORE keyword for
INSERT,
UPDATE, and so forth. If you
use it, MySQL ignores primary-key or unique-key violations and
continues processing with the next row. See the section for
the statement that you are using (Section 13.2.5, “INSERT Syntax”,
Section 13.2.11, “UPDATE Syntax”, and so forth).
You can get information about the number of rows actually
inserted or updated with the
mysql_info() C API function.
You can also use the SHOW
WARNINGS statement. See
Section 23.8.7.35, “mysql_info()”, and
Section 13.7.5.41, “SHOW WARNINGS Syntax”.
Currently, only InnoDB tables support
foreign keys. See
Section 14.8.6, “InnoDB and FOREIGN KEY Constraints”.
Foreign keys let you cross-reference related data across tables, and foreign key constraints help keep this spread-out data consistent.
MySQL supports ON UPDATE and ON
DELETE foreign key references in
CREATE TABLE and
ALTER TABLE statements. The
available referential actions are RESTRICT
(the default), CASCADE, SET
NULL, and NO ACTION.
SET DEFAULT is also supported by the MySQL
Server but is currently rejected as invalid by
InnoDB. Since MySQL does not
support deferred constraint checking, NO
ACTION is treated as RESTRICT.
For the exact syntax supported by MySQL for foreign keys, see
Section 13.1.17.3, “Using FOREIGN KEY Constraints”.
MATCH FULL, MATCH
PARTIAL, and MATCH SIMPLE are
allowed, but their use should be avoided, as they cause the
MySQL Server to ignore any ON DELETE or
ON UPDATE clause used in the same
statement. MATCH options do not have any
other effect in MySQL, which in effect enforces MATCH
SIMPLE semantics full-time.
MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created.
You can obtain information about foreign keys from the
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
table. An example of a query against this table is shown here:
mysql>SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME>FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE>WHERE REFERENCED_TABLE_SCHEMA IS NOT NULL;+--------------+---------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | +--------------+---------------+-------------+-----------------+ | fk1 | myuser | myuser_id | f | | fk1 | product_order | customer_id | f2 | | fk1 | product_order | product_id | f1 | +--------------+---------------+-------------+-----------------+ 3 rows in set (0.01 sec)
Currently, only InnoDB tables support
foreign keys. See
Section 14.8.6, “InnoDB and FOREIGN KEY Constraints”, for
information specific to foreign key support in
InnoDB.
By default, MySQL is forgiving of invalid or improper data values and coerces them to valid values for data entry. However, you can enable strict SQL mode to select more traditional treatment of bad values such that the server rejects them and aborts the statement in which they occur. See Section 5.1.7, “Server SQL Modes”.
This section describes the default (forgiving) behavior of MySQL, as well as the strict SQL mode and how it differs.
If you are not using strict mode, then whenever you insert an
“incorrect” value into a column, such as a
NULL into a NOT NULL
column or a too-large numeric value into a numeric column,
MySQL sets the column to the “best possible
value” instead of producing an error: The following
rules describe in more detail how this works:
If you try to store an out of range value into a numeric column, MySQL Server instead stores zero, the smallest possible value, or the largest possible value, whichever is closest to the invalid value.
For strings, MySQL stores either the empty string or as much of the string as can be stored in the column.
If you try to store a string that does not start with a number into a numeric column, MySQL Server stores 0.
Invalid values for ENUM and
SET columns are handled as
described in Section 1.7.3.4, “ENUM and SET Constraints”.
MySQL permits you to store certain incorrect date values
into DATE and
DATETIME columns (such as
'2000-02-31' or
'2000-02-00'). In this case, when an
application has not enabled strict SQL mode, it up to the
application to validate the dates before storing them. 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 “zero” date value
'0000-00-00' is stored in the column
instead.
If you try to store NULL into a column
that doesn't take NULL values, an error
occurs for single-row
INSERT statements. For
multiple-row INSERT
statements or for
INSERT INTO
... SELECT statements, MySQL Server stores the
implicit default value for the column data type. In
general, this is 0 for numeric types,
the empty string ('') for string types,
and the “zero” value for date and time types.
Implicit default values are discussed in
Section 11.6, “Data Type Default Values”.
If an INSERT statement
specifies no value for a column, MySQL inserts its default
value if the column definition includes an explicit
DEFAULT clause. If the definition has
no such DEFAULT clause, MySQL inserts
the implicit default value for the column data type.
The reason for using the preceding rules in nonstrict mode is that we can't check these conditions until the statement has begun executing. We can't just roll back if we encounter a problem after updating a few rows, because the storage engine 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 is better to “do the best you can” and then continue as if nothing happened.
In MySQL 5.0.2 and up, you can select stricter treatment of
input values by using the
STRICT_TRANS_TABLES or
STRICT_ALL_TABLES SQL modes:
SET sql_mode = 'STRICT_TRANS_TABLES'; SET sql_mode = 'STRICT_ALL_TABLES';
STRICT_TRANS_TABLES enables
strict mode for transactional storage engines, and also to
some extent for nontransactional engines. It works like this:
For transactional storage engines, bad data values occurring anywhere in a statement cause the statement to abort and roll back.
For nontransactional storage engines, a statement aborts
if the error occurs in the first row to be inserted or
updated. (When the error occurs in the first row, the
statement can be aborted to leave the table unchanged,
just as for a transactional table.) Errors in rows after
the first do not abort the statement, because the table
has already been changed by the first row. Instead, bad
data values are adjusted and result in warnings rather
than errors. In other words, with
STRICT_TRANS_TABLES, a
wrong value causes MySQL to roll back all updates done so
far, if that can be done without changing the table. But
once the table has been changed, further errors result in
adjustments and warnings.
For even stricter checking, enable
STRICT_ALL_TABLES. This is
the same as
STRICT_TRANS_TABLES except
that for nontransactional storage engines, errors abort the
statement even for bad data in rows following the first row.
This means that if an error occurs partway through a
multiple-row insert or update for a nontransactional table, a
partial update results. Earlier rows are inserted or updated,
but those from the point of the error on are not. To avoid
this for nontransactional tables, either use single-row
statements or else use
STRICT_TRANS_TABLES if
conversion warnings rather than errors are acceptable. To
avoid problems in the first place, do not use MySQL to check
column content. It is safest (and often faster) to let the
application ensure that it passes only valid values to the
database.
With either of the strict mode options, you can cause errors
to be treated as warnings by using
INSERT
IGNORE or UPDATE IGNORE rather
than INSERT or
UPDATE without
IGNORE.
ENUM and
SET columns provide an
efficient way to define columns that can contain only a given
set of values. See Section 11.4.4, “The ENUM Type”, and
Section 11.4.5, “The SET Type”. However, before MySQL 5.0.2,
ENUM and
SET columns do not provide true
constraints on entry of invalid data:
ENUM columns always have a
default value. If you specify no default value, then it is
NULL for columns that can have
NULL, otherwise it is the first
enumeration value in the column definition.
If you insert an incorrect value into an
ENUM column or if you force
a value into an ENUM column
with IGNORE, it is set to the reserved
enumeration value of 0, which is
displayed as an empty string in string context.
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'.
As of MySQL 5.0.2, you can configure the server to use strict
SQL mode. See Section 5.1.7, “Server SQL Modes”. With strict mode
enabled, the definition of a
ENUM or
SET column does act as a
constraint on values entered into the column. An error occurs
for values that do not satisfy these conditions:
An ENUM value must be one
of those listed in the column definition, or the internal
numeric equivalent thereof. The value cannot be the error
value (that is, 0 or the empty string). For a column
defined as
ENUM('a','b','c'), values
such as '', 'd', or
'ax' are invalid and are rejected.
A SET value must be the
empty string or a value consisting only of the values
listed in the column definition separated by commas. For a
column defined as
SET('a','b','c'), values
such as 'd' or
'a,b,c,d' are invalid and are rejected.
Errors for invalid values can be suppressed in strict mode if
you use INSERT
IGNORE or UPDATE IGNORE. In this
case, a warning is generated rather than an error. For
ENUM, the value is inserted as
the error member (0). For
SET, the value is inserted as
given except that any invalid substrings are deleted. For
example, 'a,x,b,y' results in a value of
'a,b'.
The following sections list developers, contributors, and supporters that have helped to make MySQL what it is today.
Although Oracle Corporation and/or its affiliates own all
copyrights in the MySQL server and the
MySQL manual, we wish to recognize those who
have made contributions of one kind or another to the
MySQL distribution. Contributors are listed
here, in somewhat random order:
Gianmassimo Vigazzola <qwerg@mbox.vol.it> or
<qwerg@tin.it>
The initial port to Win32/NT.
Per Eric Olsson
For constructive criticism and real testing of the dynamic record format.
Irena Pancirov <irena@mail.yacc.it>
Win32 port with Borland compiler.
mysqlshutdown.exe and
mysqlwatch.exe.
David J. Hughes
For the effort to make a shareware SQL database. At TcX, the
predecessor of MySQL AB, we started with
mSQL, but found that it couldn't satisfy
our purposes so instead we wrote an SQL interface to our
application builder Unireg. mysqladmin and
mysql client are programs that were largely
influenced by their mSQL counterparts. We
have put a lot of effort into making the MySQL syntax a
superset of mSQL. Many of the API's ideas
are borrowed from mSQL to make it easy to
port free mSQL programs to the MySQL API.
The MySQL software doesn't contain any code from
mSQL. Two files in the distribution
(client/insert_test.c and
client/select_test.c) are based on the
corresponding (noncopyrighted) files in the
mSQL distribution, but are modified as
examples showing the changes necessary to convert code from
mSQL to MySQL Server.
(mSQL is copyrighted David J. Hughes.)
Patrick Lynch
For helping us acquire http://www.mysql.com/.
Fred Lindberg
For setting up qmail to handle the MySQL mailing list and for the incredible help we got in managing the MySQL mailing lists.
Igor Romanenko <igor@frog.kiev.ua>
mysqldump (previously
msqldump, but ported and enhanced by
Monty).
Yuri Dario
For keeping up and extending the MySQL OS/2 port.
Tim Bunce
Author of mysqlhotcopy.
Zarko Mocnik <zarko.mocnik@dem.si>
Sorting for Slovenian language.
"TAMITO" <tommy@valley.ne.jp>
The _MB character set macros and the ujis
and sjis character sets.
Joshua Chamas <joshua@chamas.com>
Base for concurrent insert, extended date syntax, debugging on NT, and answering on the MySQL mailing list.
Yves Carlier <Yves.Carlier@rug.ac.be>
mysqlaccess, a program to show the access rights for a user.
Rhys Jones <rhys@wales.com> (And GWE Technologies
Limited)
For one of the early JDBC drivers.
Dr Xiaokun Kelvin ZHU <X.Zhu@brad.ac.uk>
Further development of one of the early JDBC drivers and other MySQL-related Java tools.
James Cooper <pixel@organic.com>
For setting up a searchable mailing list archive at his site.
Rick Mehalick <Rick_Mehalick@i-o.com>
For xmysql, a graphical X client for MySQL
Server.
Doug Sisk <sisk@wix.com>
For providing RPM packages of MySQL for Red Hat Linux.
Diemand Alexander V. <axeld@vial.ethz.ch>
For providing RPM packages of MySQL for Red Hat Linux-Alpha.
Antoni Pamies Olive <toni@readysoft.es>
For providing RPM versions of a lot of MySQL clients for Intel and SPARC.
Jay Bloodworth <jay@pathways.sde.state.sc.us>
For providing RPM versions for MySQL 3.21.
David Sacerdote <davids@secnet.com>
Ideas for secure checking of DNS host names.
Wei-Jou Chen <jou@nematic.ieo.nctu.edu.tw>
Some support for Chinese(BIG5) characters.
Wei He <hewei@mail.ied.ac.cn>
A lot of functionality for the Chinese(GBK) character set.
Jan Pazdziora <adelton@fi.muni.cz>
Czech sorting order.
Zeev Suraski <bourbon@netvision.net.il>
FROM_UNIXTIME() time
formatting, ENCRYPT()
functions, and bison advisor. Active
mailing list member.
Luuk de Boer <luuk@wxs.nl>
Ported (and extended) the benchmark suite to
DBI/DBD. Have been of
great help with crash-me and running
benchmarks. Some new date functions. The
mysql_setpermission script.
Alexis Mikhailov <root@medinf.chuvashia.su>
User-defined functions (UDFs); CREATE
FUNCTION and DROP
FUNCTION.
Andreas F. Bobak <bobak@relog.ch>
The AGGREGATE extension to user-defined
functions.
Ross Wakelin <R.Wakelin@march.co.uk>
Help to set up InstallShield for MySQL-Win32.
Jethro Wright III <jetman@li.net>
The libmysql.dll library.
James Pereria <jpereira@iafrica.com>
Mysqlmanager, a Win32 GUI tool for administering MySQL Servers.
Curt Sampson <cjs@portal.ca>
Porting of MIT-pthreads to NetBSD/Alpha and NetBSD 1.3/i386.
Martin Ramsch <m.ramsch@computer.org>
Examples in the MySQL Tutorial.
Steve Harvey
For making mysqlaccess more secure.
Konark IA-64 Centre of Persistent Systems Private Limited
Help with the Win64 port of the MySQL server.
Albert Chin-A-Young.
Configure updates for Tru64, large file support and better TCP wrappers support.
John Birrell
Emulation of pthread_mutex() for OS/2.
Benjamin Pflugmann
Extended MERGE tables to handle
INSERTS. Active member on the MySQL mailing
lists.
Jocelyn Fournier
Excellent spotting and reporting innumerable bugs (especially in the MySQL 4.1 subquery code).
Marc Liyanage
Maintaining the OS X packages and providing invaluable feedback on how to create OS X packages.
Robert Rutherford
Providing invaluable information and feedback about the QNX port.
Previous developers of NDB Cluster
Lots of people were involved in various ways summer students, master thesis students, employees. In total more than 100 people so too many to mention here. Notable name is Ataullah Dabaghi who up until 1999 contributed around a third of the code base. A special thanks also to developers of the AXE system which provided much of the architectural foundations for NDB Cluster with blocks, signals and crash tracing functionality. Also credit should be given to those who believed in the ideas enough to allocate of their budgets for its development from 1992 to present time.
Google Inc.
We wish to recognize Google Inc. for contributions to the MySQL distribution: Mark Callaghan's SMP Performance patches and other patches.
Other contributors, bugfinders, and testers: James H. Thompson,
Maurizio Menghini, Wojciech Tryc, Luca Berra, Zarko Mocnik, Wim
Bonis, Elmar Haneke, <jehamby@lightside>,
<psmith@BayNetworks.com>,
<duane@connect.com.au>, Ted Deppner
<ted@psyber.com>, Mike Simons, Jaakko Hyvatti.
And lots of bug report/patches from the folks on the mailing list.
A big tribute goes to those that help us answer questions on the MySQL mailing lists:
Daniel Koch <dkoch@amcity.com>
Irix setup.
Luuk de Boer <luuk@wxs.nl>
Benchmark questions.
Tim Sailer <tps@users.buoy.com>
DBD::mysql questions.
Boyd Lynn Gerber <gerberb@zenez.com>
SCO-related questions.
Richard Mehalick <RM186061@shellus.com>
xmysql-related questions and basic
installation questions.
Zeev Suraski <bourbon@netvision.net.il>
Apache module configuration questions (log & auth), PHP-related questions, SQL syntax-related questions and other general questions.
Francesc Guasch <frankie@citel.upc.es>
General questions.
Jonathan J Smith <jsmith@wtp.net>
Questions pertaining to OS-specifics with Linux, SQL syntax, and other things that might need some work.
David Sklar <sklar@student.net>
Using MySQL from PHP and Perl.
Alistair MacDonald <A.MacDonald@uel.ac.uk>
Is flexible and can handle Linux and perhaps HP-UX.
John Lyon <jlyon@imag.net>
Questions about installing MySQL on Linux systems, using
either .rpm files or compiling from
source.
Lorvid Ltd. <lorvid@WOLFENET.com>
Simple billing/license/support/copyright issues.
Patrick Sherrill <patrick@coconet.com>
ODBC and VisualC++ interface questions.
Randy Harmon <rjharmon@uptimecomputers.com>
DBD, Linux, some SQL syntax questions.
The following people have helped us with writing the MySQL documentation and translating the documentation or error messages in MySQL.
Paul DuBois
Ongoing help with making this manual correct and understandable. That includes rewriting Monty's and David's attempts at English into English as other people know it.
Kim Aldale
Helped to rewrite Monty's and David's early attempts at English into English.
Michael J. Miller Jr.
<mke@terrapin.turbolift.com>
For the first MySQL manual. And a lot of spelling/language fixes for the FAQ (that turned into the MySQL manual a long time ago).
Yan Cailin
First translator of the MySQL Reference Manual into simplified Chinese in early 2000 on which the Big5 and HK coded versions were based.
Jay Flaherty <fty@mediapulse.com>
Big parts of the Perl
DBI/DBD section in the
manual.
Paul Southworth <pauls@etext.org>, Ray Loyzaga
<yar@cs.su.oz.au>
Proof-reading of the Reference Manual.
Therrien Gilbert <gilbert@ican.net>, Jean-Marc
Pouyot <jmp@scalaire.fr>
French error messages.
Petr Snajdr, <snajdr@pvt.net>
Czech error messages.
Jaroslaw Lewandowski <jotel@itnet.com.pl>
Polish error messages.
Miguel Angel Fernandez Roiz
Spanish error messages.
Roy-Magne Mo <rmo@www.hivolda.no>
Norwegian error messages and testing of MySQL 3.21.xx.
Timur I. Bakeyev <root@timur.tatarstan.ru>
Russian error messages.
<brenno@dewinter.com> & Filippo Grassilli
<phil@hyppo.com>
Italian error messages.
Dirk Munzinger <dirk@trinity.saar.de>
German error messages.
Billik Stefan <billik@sun.uniag.sk>
Slovak error messages.
Stefan Saroiu <tzoompy@cs.washington.edu>
Romanian error messages.
Peter Feher
Hungarian error messages.
Roberto M. Serqueira
Portuguese error messages.
Carsten H. Pedersen
Danish error messages.
Arjen Lentz
Dutch error messages, completing earlier partial translation (also work on consistency and spelling).
The following is a list of creators/maintainers of some of the most important API/packages/applications that a lot of people use with MySQL.
We cannot list every possible package here because the list would then be way to hard to maintain. For other packages, please refer to the software portal at http://solutions.mysql.com/software/.
Tim Bunce, Alligator Descartes
For the DBD (Perl) interface.
Andreas Koenig <a.koenig@mind.de>
For the Perl interface for MySQL Server.
Jochen Wiedmann <wiedmann@neckar-alb.de>
For maintaining the Perl DBD::mysql module.
Eugene Chan <eugene@acenet.com.sg>
For porting PHP for MySQL Server.
Georg Richter
MySQL 4.1 testing and bug hunting. New PHP 5.0
mysqli extension (API) for use with MySQL
4.1 and up.
Giovanni Maruzzelli <maruzz@matrice.it>
For porting iODBC (Unix ODBC).
Xavier Leroy <Xavier.Leroy@inria.fr>
The author of LinuxThreads (used by the MySQL Server on Linux).
The following is a list of some of the tools we have used to create MySQL. We use this to express our thanks to those that has created them as without these we could not have made MySQL what it is today.
Free Software Foundation
From whom we got an excellent compiler
(gcc), an excellent debugger
(gdb and the libc
library (from which we have borrowed
strto.c to get some code working in
Linux).
Free Software Foundation & The XEmacs development team
For a really great editor/environment.
Julian Seward
Author of valgrind, an excellent memory
checker tool that has helped us find a lot of otherwise hard
to find bugs in MySQL.
Dorothea Lütkehaus and Andreas Zeller
For DDD (The Data Display Debugger) which
is an excellent graphical front end to
gdb).
Although Oracle Corporation and/or its affiliates own all
copyrights in the MySQL server and the
MySQL manual, we wish to recognize the
following companies, which helped us finance the development of
the MySQL server, such as by paying us for
developing a new feature or giving us hardware for development of
the MySQL server.
VA Linux / Andover.net
Funded replication.
NuSphere
Editing of the MySQL manual.
Stork Design studio
The MySQL Web site in use between 1998-2000.
Intel
Contributed to development on Windows and Linux platforms.
Compaq
Contributed to Development on Linux/Alpha.
SWSoft
Development on the embedded mysqld version.
FutureQuest
The --skip-show-database
option.