Triggers are stored program units that are implicitly executed when DDL or DML statements are used on associated tables. They define procedures to enforce business rules, prevent invalid transactions, and provide information on user events. Triggers can be row or statement level and fire before, after, or instead of insert, update, or delete operations. They are comprised of a trigger event, optional restriction, and action to execute.

1. Triggers
Mrs. Amrit Kaur
gamritkaur@live.com

2. What is a Trigger?
• Triggers defines procedures that are
IMPLICITLY EXECUTED when any DDL or DML
statement is used against associated table.
• Trigger VS Stored Procedures
– Triggers are implicitly fired (automatic execution).
– Stored Procedure explicitly executed by USER.

3. How to USE Triggers
• Prevent invalid transaction
• Enforce referential integrity
• Enforce Complex business rules
• Provide information about user events, user
logging etc.

4. Parts of Trigger
CREATE OR REPLACE TRIGGER trigger_name
{BEFORE | AFTER | INSTEAD OF }
{INSERT | DELETE | UPDATE |
OF column_name ON table_name
[REFERENCING OLD AS o NEW AS n]
[FOR EACH ROW]
WHEN (condition)
DECLARE
............
BEGIN
........
END;
Trigger Event or Statement1
Trigger Action3
Trigger Restriction2

5. Parts of Trigger
• Trigger Event or Statement
– An event that cause trigger to fire
• Trigger Restriction
– Test this condition if specified trigger event occurs
– Must be true for trigger to fire

6. Parts of Trigger
• Trigger Action
– Statement (s) to be executed when trigger is fired.
– Can contain
• SQL,
• PL/SQL,
• call to stored procedure etc.

7. Types of Trigger
• Row Trigger
– Executed ONCE for every row affected by triggering
statement.
– Identified by including FOR EACH ROW clause in
CREATE TRIGGER statemeny
• Statement Trigger
– Fired ONCE no matter how many times row affected.
– Default type of trigger

8. Types of Trigger
• BEFORE and AFTER TRIGGER
– Can only be define on Table not on Views.
– BEFORE Trigger
• Runs Trigger action BEFORE executing triggering
statement.
– AFETR Trigger
• Runs Trigger action AFTER executing triggering
statement.

9. Types of Trigger
• INSTEAD OF Trigger
– Can be created on both tables as well as views.
– Used to perform an action on another table or
view.

10. View Defined Triggers
• Use data dictionary USER_TRIGGERS to list all
defined triggers
• USER_TRIGGERS include
– Columns,
– Trigger Name
– Trigger Type
– Trigger Event
– Referencing Names
– Trigger Body

11. Enable / Disable Trigger
• ALTER TRIGGER statement is used to enable or
disable triggers
ALTER TRIGGER trigger_name {ENABLE | DISABLE}

12. Dropping Table
• DROP TRIGGER statement is used to delete
trigger.
DROP TRIGGER trigger_name;