PL/SQL: TRIGGERS INTRO

Named PL/SQL blocks which are stored in database are called triggers.
Or
Specialized stored programs which executes implicitly when trigger event occurs.
Events:
Events may be anything,
such as
1. DML statement, which includes insert or delete statement.
2. DDL statement, which includes create or alter statements.
3. System event, which includes shutdown or restart database.
4. User event, Which include logoff or log on of user on the database.

TYPES of TRIGGERS:
There are 5 types of trigges.

1. DML TRIGGERS.
As name show, this type or trigger fire with the dml statements, before or after the insert, delete or update statement.

2. DDL TRIGGERS:
These are the triggers which are created with the ddl statements, such as create or alter statement, These triggers fire when any changes occure.

3. SYSTEM EVENT TRIGGERS:
This type of triggers occure when database or system event occur, such as logon or log off of the database.

4. INSTEAD-OF TRIGGERS:
These tirggers enables you to stop or redirected the performance of dml triggers.

5. COMPOUND TRIGGERS:
These are multi tasking triggers that act as low level triggers when the data inserted, deleted or updated from the database table. Compound triggers used to audit, check, replace or save even before the change.