Triggers are stored procedures that are automatically executed in response to data modification events like insert, update or delete on a table. There are two types of triggers - DML triggers which respond to data manipulation statements, and DDL triggers which respond to data definition language statements like create, alter or drop. Triggers can be used to perform validation, auditing or other actions in response to data changes. They can be disabled, enabled or modified as needed using SQL statements.

2. Index:-
 Implementation of Triggers
 Example
 Types of Triggers
 DML Triggers
 DDL Triggers
 Recursive and Nested Triggers
 Disabling Trigger, Enabling Triggers, Modifying
Triggers

3. Triggers
 Triggers are special types of Stored Procedures that are
ran automatically by the database whenever a certain
modification (event) occurs.
 The modification statements may include
INSERT, UPDATE, and DELETE.
 User cannot fire the trigger explicitly , it gets fired
implicitly on the basis of certain specified event
 Not a stand alone object

4. Example:-
 If you write a letter to your friend and then drop it in a mailbox without
putting enough postage on the envelope, you trigger the post office to
return the letter to you along with a friendly reminder that you need to
add postage. This reminder is triggered by the lack of a stamp;
otherwise, the letter would have gone through the mail without any
delays.
 Different post office triggers would be invoked if you provided enough
postage but forgot to write your friend’s address

5. Types of Triggers:
 We can create TWO types of triggers:
1) DML (data manipulation language) triggers
 DML triggers run when insert, update or delete statements
modify data in the specified table or view.
 Insert : triggers are invoked by insert statement
 Update: triggers are invoked by update statement
 Delete : triggers are invoked by delete statement
CONT…..

6. Types of Triggers:
2) DDL (data definition language) triggers
 DDL triggers run when events such as creating, altering or
dropping an object occurs on the server
 Used for database administration tasks such as auditing and
controlling object access.

7. Triggers can get fired in two different MODES:
1) For/After Trigger:
• It gets fired only after the sql server completes all actions
successfully on a specified table.
• Can rollback all the earlier transactions by issuing ROLLBACK
• For example on inserting a row on a table, the trigger defined on
the INSERT operation fires only after the row gets successfully
inserted and if the insert fails sql does not execute the trigger.
• 2) Instead of Trigger:
• It causes the code present in the trigger to execute instead of
the operation that caused the trigger to fire.
• If we define INSTEAD OF Trigger on the above mentioned
table, insert would not happen but the trigger gets fired

8. For / After Trigger:
Insert/update/dele
te into/from table
Inserts/ updates/
deletes the value
in the table
Fires the trigger
Inserts the
value in the
INSERTED
/DELETED
table as well
Can be
Rolled back
Using
ROLLBACK
Executes SQL
of TRIGGER

9. Instead Of Trigger:
Insert /Update/Delete
command
Table
INSTEAD OF
Insert/Update/Delete
trigger
INSTEAD
OFINSTEAD
OF
Executes the
querry in the
trigger

10. Syntax of Trigger:
 CREATE TRIGGER trigger_name
ON { table | view }
[ WITH ENCRYPTION ]
{
{ {FOR | AFTER | INSTEAD OF }
{ [ INSERT ] [ , ] [ UPDATE ] [ , ] [ DELETE ] }
AS
sql_statement [...n ]
}
} CONT……..
DML Trigger:

11. Arguments:
 Trigger_name:
Is the name of the trigger.
 Table | view
Is the table or view on which the trigger is executed
 WITH ENCRYPTION
Code in the trigger will be encrypted when it is created
 AFTER
Specifies that the trigger is fired only when all operations
specified in the triggering SQL statement have executed
successfully
 INSTEAD OF
Specifies that the trigger is executed instead of the
triggering SQL statement

12. Arguments:
 { [DELETE] [,] [INSERT] [,] [UPDATE] }
Are keywords that specify which data modification
statements, when attempted against the table or view,
activate the trigger.
 WITH APPEND
Specifies that an additional trigger of an existing type
should be added.
 NOT FOR REPLICATION
Indicates that the trigger should not be executed when
a replication process modifies the table involved in the
trigger

13. Syntax of Trigger:
 CREATE TRIGGER trigger_name
ON { ALL SERVER | DATABASE }
[ WITH ENCRYPTION ]
{
{ {FOR | AFTER }
{ event_type | event_group } [ ,...n ]
AS
sql_statement [...n ]
}
}
CONT……..
DDL Trigger:

14. Arguments:
 DATABASE
If specified, the trigger fires whenever event_type or
event_group occurs in the current database.
 ALL SERVER
If specified, the trigger fires whenever event_type or
event_group occurs anywhere in the current server.
 event_type
Is the name of a Transact-SQL language event that, after
execution, causes a DDL trigger to fire. (create, alter, drop)
 event_group
The DDL trigger fires after execution of any Transact-SQL
language event that belongs to event_group.

15.  Event types…..
 Create: certificate, assembly, index, function,
procedure, role, rule etc……..
 Alter: certificate, assembly, index, function,
procedure, role, rule etc……..
 Drop: certificate, assembly, index, function,
procedure, role, rule etc……..

16. Working /Magic Tables :
 Triggers have access to two special tables called :
 Inserted and deleted.
Insert operation
Delete operation
Update
operation
INSERTED DELETED
Each row that was inserted
in the table
Each row that was deleted
From the table
Has after image of the row
updated
Has before image of the
row updated
CONT……..
Deleted table
will be Empty
Inserted table
will be empty

17. Recursive and Nested Triggers:
 Recursive Triggers:
 A trigger that cause itself to fire is called recursive trigger.
 For example update trigger is created on boat table that modifies
a column in boat table, the modification in the trigger causes the
trigger to fire again leading to an unending chain of transactions.
 For this in sql server by default the RECURSIVE_TRIGGERS
option is set off and you must explicitly turn on this option
BOAT table
UPDATE Statement
UPDATE
Trigger
Update statement fires
the update trigger
Updates the
column
Update boat table

18.  Nested Triggers:
COMPANY
Table
EMPLOYEE
Table
UPDATE
Trigger
UPDATE
Trigger
UPDATE Statement

19. Trigger firing order:
 sp_settriggerorder [@triggername =] '<trigger name>',
 [@order =] '{FIRST|LAST|NONE}',
 [@stmttype =] '{INSERT|UPDATE|DELETE}'

20. Common Use of Trigger:
 Referential Integrity.
 Data Integrity Rules
 Creating Audit Trails:
 Functionality similar to a CHECK constraint, but
which works across tables, databases, or even servers.
 etc……..

21. Actions that cannot be performed using
triggers:
 Database cannot be created, altered, dropped, backed
up or restored.
 Structural changes cannot be made to table that
caused trigger to fire.
 Sql server does not support triggers against system
objects.
 Triggers gets fired only in response to logged
operations hence minimally logged operations such as
TRUNCATE and WRITETEXT do not cause triggers to
fire.

22. Disabling Triggers:-
 Sometimes triggers can get in the way of what we are trying to
accomplish.
 For example, suppose that we wrote complex triggers on a table to
perform a variety of data integrity and validation checks to protect
database from incorrect information.
 Now suppose that we are given a text file containing several million
rows of cleaned data that needs to be inserted into this table.
 These triggers will likely get in the way and cause the data load to take a
very long time.
 Here we can use the DISABLE TRIGGER statement to tell SQL Server
2005 to set one or more triggers:
DISABLE TRIGGER Trigger name ON Tablename
CONT…..

23. Disabling Triggers:-
 If you want to disable all triggers for a table
DISABLE TRIGGER ALL ON TABLENA ME
 Disables all DDL triggers for the whole database
DISABLE TRIGGER ALL ON DATABASE
 Disable all the DDL triggers for the entire server
DISABLE TRIGGER ALL ON ALL SERVER
CONT……

24. Disabling Triggers:-
 Check whether the trigger is active or not
 SELECT name,
is_disabled
FROM sys.triggers
WHERE name = ‘TRIGGER_NAME’
 A value of ‘1’ in disabled column means that the
trigger is disabled; a value of ‘0’ means that it is active

25. Enabling Triggers:-
 If you want to disable all triggers for a table
ENABLE TRIGGER ALL ON TABLENAME
 Disables all DDL triggers for the whole database
ENABLE TRIGGER ALL ON DATABASE
 Disable all the DDL triggers for the entire server
ENABLE TRIGGER ALL ON ALL SERVER

26. Modifying Triggers:-
 If you need to make a modification to the trigger’s
logic, you can use the ALTER TRIGGER statement.
 Altering a trigger often means that you must re-type
the code for the entire trigger. For this you can retrieve
it by simply running the sp_helptext stored procedure:
 Sp_helptext trigger_name
 On the other hand, if you want to rename the trigger,
use the combination of
 DROP TRIGGER and CREATE TRIGGER statements

27. Deleting Triggers:-
 For a DML trigger, the DROP TRIGGER statement
looks like this:
 DROP TRIGGER Trigger_name
 Getting rid of a DDL trigger for just one database looks
like this:
 DROP TRIGGER Trigger_name ON DATABASE
 DROP TRIGGER statement to remove a DDL trigger
for all databases on your server:
 DROP TRIGGER Trigger_name ON ALL SERVER

28. References:
 www.theparticle.com/cs/bc/dbms/triggers.pdf
 www.sql-server-
performance.com/articles/dev/triggers_2000_p6.aspx
 Microsoft SQL Server 2005 Implementation And
Maintenance .
 SQL Server 2005 Bible.