SET
语法
SET variable_assignment [, variable_assignment] ... variable_assignment: user_var_name = expr | [GLOBAL | SESSION] system_var_name = expr | [@@global. | @@session. | @@]system_var_name = expr
可以在任意表达式中使用下面的语法设置用户变量:
user_var_name:= expr
描述
SET
语句可以为影响服务端或客户端的不同变量类型进行赋值。老版本的MySQL采用SET OPTION
,但是不赞成使用带有OPTION
的SET
语法,且其在MariaDB 10.0版本中已经移除。
要为基于每查询(per-query)(从MariaDB 10.1.2之后开始的功能)的变量赋值,参见SET STATEMENT
。
要查看服务端系统变量,可参见SHOW VARIABLES
。
Server System Variables列出了所有的系统变量。
示例
SHOW VARIABLES WHERE Variable_name LIKE "aria_group_commit%"; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | aria_group_commit | none | | aria_group_commit_interval | 0 | +----------------------------+-------+ SET GLOBAL aria_group_commit="HARD"; SET GLOBAL aria_group_commit_interval=100; SHOW VARIABLES WHERE Variable_name LIKE "aria_group_commit%"; +----------------------------+-------+ | Variable_name | Value | +----------------------------+-------+ | aria_group_commit | hard | | aria_group_commit_interval | 100 | +----------------------------+-------+
直接赋值:
SELECT (@a:=1); +---------+ | (@a:=1) | +---------+ | 1 | +---------+ SELECT @a; +------+ | @a | +------+ | 1 | +------+
See Also
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