Oracle Before INSERT/UPDATE/DELETE Trigger

This statement specifies that Oracle will fire this trigger BEFORE the INSERT/UPDATE or DELETE operation is executed.

Syntax

 CREATE [ OR REPLACE ] TRIGGER trigger_name  

BEFORE INSERT or UPDATE or DELETE  

 ON table_name  

  [ FOR EACH ROW ]  

DECLARE  

   -- variable declarations  

BEGIN  

   -- trigger code  

EXCEPTION  

   WHEN ...  

   -- exception handling  

END; 

Parameters

OR REPLACE: It is an optional parameter. It is used to re-create the trigger if it already exists. It facilitates you to change the trigger definition without using a DROP TRIGGER statement.

trigger_name: It specifies the name of the trigger that you want to create.

BEFORE INSERT or UPDATE or DELETE: It specifies that the trigger will be fired before the INSERT or UPDATE or DELETE operation is executed.

table_name: It specifies the name of the table on which trigger operation is being performed.

Limitations

• BEFORE trigger cannot be created on a view.
• You cannot update the OLD values.
• You can only update the NEW values.

Oracle BEFORE Trigger Example

Consider, you have a “suppliers” table with the following parameters.

CREATE TABLE  "SUPPLIERS"   

   (    "SUPPLIER_ID" NUMBER,   

    "SUPPLIER_NAME" VARCHAR2(4000),   

    "SUPPLIER_ADDRESS" VARCHAR2(4000)  

   )  

/

You can use the following CREATE TRIGGER query to create a BEFORE INSERT or UPDATE or DELETE Trigger:

CREATE OR REPLACE TRIGGER  "SUPPLIERS_T1"   

BEFORE  

insert or update or delete on "SUPPLIERS"  

for each row  

begin  

when the person performs insert/update/delete operations into the table.  

end;  

/  

ALTER TRIGGER  "SUPPLIERS_T1" ENABLE  

/

Here the trigger name is “SUPPLIERS_T1” and it is fired BEFORE the insert or update or delete operation is executed on the table “suppliers”.