Oracle trigger before update | Trigger before insert | Trigger before delete - oracle tutorial - sql tutorial



How to trigger BEFORE INSERT/UPDATE or DELETE in Oracle ?

  • BEFORE triggers run the trigger action before the triggering statement is run. This type of trigger is commonly used in the following situations:
  • When the trigger action determines whether the triggering statement should be allowed to complete.
  • Using a BEFORE trigger for this purpose, you can eliminate unnecessary processing of the triggering statement and its eventual rollback in cases where an exception is raised in the trigger action.
  • To derive specific column values before completing triggering INSERT or UPDATE statement.
  • This statement specifies that Oracle will fire this trigger BEFORE the INSERT/UPDATE or DELETE operation is executed.
  • Oracle sql trigger

    Oracle sql trigger

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;  
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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 sql create trigger query

Oracle sql create trigger query

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)  
)  
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  • 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  
/  
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  • 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".
 Before Trigger

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