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A trigger is a special type of stored procedure, which is different from the general stored procedure described earlier.

The general stored procedure is called directly through the name of the stored procedure, while the trigger is mainly triggered by the event.

Triggers are a powerful tool that is automatically enforced when data changes in a table.

Triggers can be used to check the integrity of SQL Server constraints, default values, and rules

You can also perform complex functions that are difficult to implement with ordinary constraints.

What on earth is a trigger?

In SQL Server, that is, a certain operation on a table, triggering a certain condition, and thus the execution of a program.

A trigger is a special stored procedure.

There are three common triggers: applied to Insert, Update, and Delete events

Common grammar

CREATE TRIGGER triggerName ON TableName

For UPDATE | INSERT | DELETE

AS

Begin

Select * from updated

-- inserted

-- deleted

End

Create trigger tem on employees for delete

As

Begin

Declare @ num int

Select @ num=count (*) from deleted

If @ num > 2

Print 'delete a maximum of 2 entries at a time'

Rollback transaction

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