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
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 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".
