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什么是触发器?
触发器也是一种存储过程,当给定表或视图上发生事件时,触发器将自动执行。
仅对给定的<subject_table_name>具有TRIGGER特权的数据库用户被允许为该表或视图创建触发器。
CREATE TRIGGER命令定义在给定主题表或主题视图上执行给定操作(INSERT / UPDATE / DELETE)时执行的一组语句。
句法
CREATE TRIGGER <TRIGGER_NAME> <trigger_action_time> <trigger_event_list> ON <subject_table_name> [REFERENCING <transition_list>] [<for_each_row>] BEGIN [<trigger_decl_list>] [<proc_handler_list>] <trigger_stmt_list> END
SYNTAX ELEMENTS
ELEMENTS | DESCRIPTION |
---|---|
<trigger_name> | It specifies the name of the trigger to be created, with the optional schema name. |
<trigger_action_time> | BEFORE | AFTER | INSTEAD OF • BEFORE - Specifies that the trigger will be executed before the DML Operation on a table. • AFTER - Specifies that the trigger will be executed after the DML operation on a table. • INSTEAD OF - Specifies that the trigger will be executed instead of the DML operation on a view. A view with INSTEAD OF trigger becomes updatable. |