AFTER TRIGGER in Oracle

ORACLE AFTER TRIGGER
As the name itself suggests, AFTER 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 AFTER Trigger. It can also be used to replace an already existing trigger and thus to change the trigger definition.

Types of the Oracle AFTER trigger:
There are mainly three types of AFTER Trigger in Oracle:

• AFTER INSERT TRIGGER
• AFTER UPDATE TRIGGER
• AFTER DELETE TRIGGER

Limitations of the Oracle AFTER trigger:

• Creation on a view is not possible with the Oracle AFTER trigger.
• OLD values cannot be updated.
• The update feature is only possible for the NEW values.

Syntax:

CREATE OR REPLACE TRIGGER trigger_name  
AFTER INSERT or UPDATE or DELETE  
ON table_name  
FOR EACH ROW
DECLARE  
declarations of variables 
BEGIN  
trigger code  
EXCEPTION  
WHEN conditions
exception handling  
END;  

Parameters:
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.

Example:
Students Table:

Create Trigger code:

CREATE OR REPLACE TRIGGER  "STUDENTS_T"   
AFTER 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  
/

Output:

TRIGGER NAME	TRIGGER TYPE      TRIGGERING EVENT	                    STATUS
STUDENTS_T	       AFTER EACH ROW	   INSERT or UPDATE or DELETE	           ENABLED

Explanation:
The ‘students’ is an already existing table and a trigger is created with the name “STUDENTS_T”. AFTER the INSERT, UPDATE or DELETE statement is issued on the table “STUDENTS”, the Oracle database will fire the trigger.