Road Map to DB2 Programming

Triggers

	SQL Reference	Describes SQL syntax, semantics, and the rules of the language. Chapters 2 and 6 contains details about triggers.
	Embedded SQL Programming Guide	Explains how to develop applications that access DB2 databases using embedded SQL. Chapter 8 contains details about triggers.
	Administration Guide	Contains information required to design, implement, and maintain a database. Chapter 4 contains details about triggers.

		Embedded SQL	DB2 CLI
	trigsql	X		Demonstrates triggers and constraints.

A trigger defines a set of actions that are executed at, or triggered by, a delete, insert or update operation on a specified table. When such an SQL operation is executed, the trigger is said to be activated. The trigger can be activated before the SQL operation or after it. You define a trigger using the SQL statement CREATE TRIGGER.

You can use triggers that run before an update or insert in several ways:

• To check or modify values before they are actually updated or inserted in the database. This is useful if you need to transform data from the way the user sees it to some internal database format.

• To run other non-database operations coded in user-defined functions.

Similarly, you can use triggers that run after an update or insert in several ways:

• To update data in other tables. This is useful for maintaining relationships between data or in keeping audit trail information.

• To check against other data in the table or in other tables. This is useful to ensure data integrity when referential integrity constraints aren't appropriate, or when table check constraints limit checking to the current table only.

• To run non-database operations coded in user-defined functions. This is useful when issuing alerts or to update information outside the database.

Figure 12. Inserts can activate a trigger

You gain several benefits using triggers:

Faster application development

Triggers are stored in the database, and are available to all applications. This relieves you of the need to code equivalent functions for each application.

Global enforcement of business rules

Triggers are defined once, and are used by all applications that use the data governed by the triggers.

Easier maintenance

Any changes need to be made only once in the database instead of in every application that uses a trigger.

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