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.

SQL标准自1986年以来一直在发展several versions exist. In this manual,“SQL-92”refers to the standard released in 1992.“SQL:1999”,“SQL:2003”,“SQL:2008”, and“SQL:2011”refer to the versions of the standard released in the corresponding years, with the last being the most recent version. 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. TheHANDLERinterface is an example of this strategy. SeeSection 13.2.4, “HANDLER Statement”.

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.

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 theNDBCLUSTERstorage engine. SeeChapter 23,MySQL NDB Cluster 8.0.

We implement XML functionality which supports most of the W3C XPath standard. SeeSection 12.12, “XML Functions”.

MySQL supports a native JSON data type as defined by RFC 7159, and based on the ECMAScript standard (ECMA-262). SeeSection 11.5, “The JSON Data Type”. MySQL also implements a subset of the SQL/JSON functions specified by a pre-publication draft of the SQL:2016 standard; seeSection 12.18, “JSON Functions”, for more information.

Selecting SQL Modes

The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients, depending on the value of thesql_modesystem 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, seeSection 5.1.11, “Server SQL Modes”.

Running MySQL in ANSI Mode

To run MySQL Server in ANSI mode, startmysqldwith the--ansioption. 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';

你可以看到设置sql_modesystem 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--ansiis not quite the same as setting the SQL mode to'ANSI'because the--ansioption also sets the transaction isolation level.

SeeSection 5.1.7, “Server Command Options”.