Triggers

What is a Trigger


A trigger is a special kind of a store procedure that executes in response to certain action on the table like insertion, deletion or updation of data. It is a database object which is bound to a table and is executed automatically. You can’t explicitly invoke triggers. The only way to do this is by performing the required action no the table that they are assigned to.

Types Of Triggers


There are three action query types that you use in SQL which are INSERT, UPDATE and DELETE. So, there are three types of triggers and hybrids that come from mixing and matching the events and timings that fire them.


Basically, triggers are classified into two main types:-


(i) After Triggers (For Triggers)

(ii) Instead Of Triggers


(i) After Triggers


These triggers run after an insert, update or delete on a table. They are not supported for views.

AFTER TRIGGERS can be classified further into three types as:


(a) AFTER INSERT Trigger-This trigger is fired after an INSERT on the table.

(b) AFTER UPDATE Trigger-This trigger is fired after an update on the table.

(c) AFTER DELETE Trigger-This trigger is fired after a delete on the table.


These can be used as an interceptor for anything that anyonr tried to do on our table or view. If you define an Instead Of trigger on a table for the Delete operation, they try to delete rows, and they will not actually get deleted (unless you issue another delete instruction from within the trigger)



INSTEAD OF TRIGGERS can be classified further into three types as:-


(a) INSTEAD OF INSERT Trigger.

(b) INSTEAD OF UPDATE Trigger.

(c) INSTEAD OF DELETE Trigger.