ORACLE BEFORE TRIGGER
As the name itself suggests, before the INSERT, UPDATE or DELETE statement is issued, the Oracle database will fire this trigger, or in other words when an INSERT, UPDATE or DELETE statement is issued these triggers can be implicitly executed. On the basis of the Firing Point, it is named as the BEFORE Trigger. It can also be used to replace an already existing trigger and thus to change the trigger definition.
Types of the Oracle BEFORE trigger:
There are mainly three types of Before Trigger in Oracle:
- BEFORE INSERT TRIGGER
- BEFORE UPDATE TRIGGER
- BEFORE DELETE TRIGGER
Limitations of the Oracle BEFORE trigger:
- Creation on a view is not possible with the Oracle BEFORE trigger.
- OLD values cannot be updated.
- The update feature is only possible for the NEW values.
CREATE OR REPLACE TRIGGER trigger_name BEFORE INSERT or UPDATE or DELETE ON table_name FOR EACH ROW DECLARE declarations of variables BEGIN trigger code EXCEPTION WHEN conditions exception handling END;
trigger_name: It is used to specify the name of the trigger to be created.
table_name: It is used to specify the name of the table on which trigger procedure will be executed.
Create Trigger code:
CREATE OR REPLACE TRIGGER "STUDENTS_T" BEFORE INSERT or UPDATE or DELETE ON "STUDENTS" FOR EACH ROW BEGIN WHEN the person performs insert/update/delete operations into the table. END; / ALTER TRIGGER "STUDENTS_T" ENABLE /
TRIGGER NAME TRIGGER TYPE TRIGGERING EVENT STATUS STUDENTS_T BEFORE EACH ROW INSERT or UPDATE or DELETE ENABLED
The ‘students’ is an already existing table and a trigger is created with the name “STUDENTS_T”. Before the INSERT, UPDATE or DELETE statement is issued on the table “STUDENTS”, the Oracle database will fire the trigger.