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;
