Triggers in Sql Server

Introduction

We can define a Trigger as "A Trigger is a Database object just like a stored procedure or we can say it is a special kind of Stored Procedure which fires when an event occurs in a database.".

Difference between Stored Procedure and trigger 

Triggers fire implicitly while Stored Procedures fire explicitly.

Type of Triggers

There are two types of Triggers:

1. DDL Trigger
2. DML trigger

DDl Triggers

They fire in response to DDL (Data Definition Language) command events that start with Create, Alter and Drop. Like Create_table, Create_view, drop_table, Drop_view and Alter_table.

Code of DDL Trigger

create trigger saftey
on database
for
create_table,alter_table,drop_table
as
print'you can not create ,drop and alter table in this database'
rollback;

When we create, alter or drop any table in a database then the following message appears:

DML Triggers

They fire in response to DML (Data Manipulation Language) command events that start with with Insert, Update and Delete. Like insert_table, Update_view and Delete_table.

create trigger deep
on emp
for
insert,update,delete
as
print'you can not insert,update and delete this table i'
rollback;

When we insert, update or delete in a table in a database then the following message appears:

DML triggers are two type

AFTER Triggers

AFTER triggers are executed after the action of an INSERT, UPDATE, or DELETE statement.

create trigger insertt
on emp
after insert
as
begin
insert into empstatus values('active')
end

INSTEAD Of Triggers

It will tell the database engine to execute the trigger instead of executing the statement. For example an insert trigger executes when an event occurs instead of the statement that would insert the values in the table . 

CREATE TRIGGER instoftr
ON v11
INSTEAD OF INSERT
AS
BEGIN
INSERT INTO emp
SELECT I.id, I.names
FROM INSERTED I

INSERT INTO emp1values
SELECT I.id1, I.name1
FROM INSERTED I
END

When we insert data into a view by the following query then it inserts values in both tables :

insert into v11 values(1,'d','dd')

You can see both tables by the folowing query:

select * from emp
select * from emp1values

Summary

In this article I described Triggers in SQL Server. I hope this article has helped you in understanding this topic. Please share it. If you know more about this, your feedback and constructive contributions are welcome.