Triggers:

This chapter displays how to enforce complex constraints using the concept known as Triggers. The trigger involves PL/SQL statements which get automatically invoked whenever any DML operations are performed on a table.

• Understanding Triggers
• Types of Triggers
• Designing Triggers
• Writing Trigger body
• Using INSTEAD OF triggers
• Enabling and Disabling triggers

A database trigger is a stored PL/SQL block which is related with a table. The Triggers are automatically executed when a specified SQL statement is issued against the table. Triggers are commonly used for the subsequent purposes:

• To automatically produce values
• To give auditing.
• To give invalid transactions.
• To look for complex integrity constraints that cannot be provided in Constraints
• To maintain replicate tables.

Triggers hold PL/SQL constructs and they can be fired only for DML Statements such as INSERT, UPDATE and DELETE. A Trigger is event based.