SQL Triggers

SQL Triggers:

Triggers are like events which can be fired after performing some operation.

Triggers are fired when some modification to data is performed.

Triggers can be fired after update,delete and insert operations.

General Syntax For Creating a Trigger:

create trigger trigger_name on table_name

AFTER insert,update,delete

 as

statements to be executed after trigger fires 

Trigger Which Fires After update:

Let's see what this trigger do.

Give trigger name as in examle that is(updatetrig) then specify

table name as(doctor) in example

create trigger updatetrig on doctor

--Define when trigger fires as in this case it fires after update 

AFTER update

as

--Define what to perform when trigger fires

select * from doctor where doctor_id='d101' 

 

--To fire trigger update a record in the table

update doctor set name='mairaj' where doctor_id='d101'

Trigger Which Fires After Delete:

create trigger deltrig on doctor

--You can perform any task after trigger fires

AFTER delete

as

--As i am deleting two records after trigger fires

                                               

delete from appointment where doctor_id='d101'

delete from doctor where doctor_id='d101'

Trigger Which Fires After Insert:

create trigger Inserttrig on doctor

AFTER insert

as

select * from doctor --Display all records 

                                               

Deleting a Trigger:

--To delete a trigger write following query as I am deleting Updatetrig

drop trigger updatetrig 

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