A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server. DML triggers execute when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.
You can use triggers in a situation where you need to perform any calculation at the time of insert, update and delete operation.
For eg: In case of delete if you want add the same value in another table to maintain history.
Triggers can not be invoked manually, it will execute automatically.
You can not use triggers on SP.
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