What is a Trigger?

What is a Trigger?
A trigger is a pl/sql block structure which is fired when a DML statements like Insert, Delete, Update is executed on a database table. A trigger is triggered automatically when an associated DML statement is executed.
Syntax of Triggers

The Syntax for creating a trigger is:
 CREATE [OR REPLACE ] TRIGGER trigger_name
 {BEFORE | AFTER | INSTEAD OF }
 {INSERT [OR] | UPDATE [OR] | DELETE}
 [OF col_name]
 ON table_name
 [REFERENCING OLD AS o NEW AS n]
 [FOR EACH ROW]
 WHEN (condition) 
 BEGIN
   — sql statements 

 END; 
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