Chapter 8, Problem 21RQ

Explanation of Solution

Trigger:

The trigger is a named set of SQL statement that is executed at the time of data modification or meets some data description.

• If the stated when trigger condition meets up, then the mentioned action in the trigger has been performed.

A trigger contains three parts and they are explained as shown below:

Event:

It specifies the change to be made, such as an UPDATE or DELETE of a record.

Condition:

It specifies the condition to examine the records about to be affected. For each record, that meets the condition given in the trigger.

Action:

The action performed after the start of the trigger.

The syntax to create a trigger is as given below:

CREATE TRIGGER trigger_name

{BEFORE| AFTER|INSTEAD OF} {INSERT|DELETE|UPDATE} ON

table_name

[FOR EACH{ROW|STATEMENT}] [WHEN(condition)]

<triggered SQL statement here>;

Purpose of trigger:

The purpose of trigger is given below:

• For enforcement of business or security constraints...