Chapter 23

Triggers

IN THIS CHAPTER

Bullet Creating triggers

Bullet Considerations in firing a trigger

Bullet Executing a trigger

Bullet Firing multiple triggers

In the course of executing a database application, occasions may arise where if some specific action occurs, you want that action to cause another action, or perhaps a succession of actions, to occur. In a sense, that first action triggers the execution of the following actions. SQL provides the TRIGGER mechanism to provide this capability.

Triggers, of course, are best known as those parts of a firearm that cause it to fire. More generally, a trigger is an action or event that causes another event to occur. In SQL, the word trigger is used in this more general sense. A triggering SQL statement causes another SQL statement (the triggered statement) to be executed.

Examining Some Applications of Triggers

The firing of a trigger is useful in a number of situations. One example is to perform a logging function. Certain actions that are critical to the integrity of a database — such as inserting, editing, or deleting a table row — could trigger the ...

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