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MySQL 5.7 Reference Manual  /  ...  /  MySQL Extensions to Standard SQL

1.8.1 MySQL Extensions to Standard SQL

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 KEY_BLOCK_SIZE clause in the following comment is executed only by servers from MySQL 5.1.10 or higher:

CREATE TABLE t1(a INT, KEY (a)) /*!50110 KEY_BLOCK_SIZE=1024 */;

The following descriptions list MySQL extensions, organized by category.

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