What is a trigger? How to create a trigger?

What is a trigger?

• #Triggers are used to "automatically" perform some operations after/before certain operations. (For example, if new student information is inserted, the number of students should be modified in the class table).

• After insert delete update sets the trigger, executing the insert delete update operation will automatically trigger the set content.

• A table can have up to 6 triggers (3*2, three operations*two times (before|after)).

Create trigger

Syntax:

create trigger 触发器名 before|after 事件 on 表名 for each row 触发器语句;

• The trigger name is recommended to be trigger_xxx, so that it is easy to distinguish, trigger names cannot be repeated.

• before|after represents the trigger statement execution time. If it is before, the trigger statement is executed before the insert delete update operation; after is after.

• The event is one of the insert delete update operations.

• for each row is a trigger that will trigger the corresponding operation on behalf of any record.

• The trigger statement is the statement to be executed when the trigger is fired.

Recommended tutorial: mysql tutorial

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