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Triggers are stored programs that are fired automatically when some events occur. The code to be fired can be defined as per the requirement.
Oracle has also provided the facility to mention the event upon which the trigger needs to be fire and the timing of the execution
Benefits of Triggers :
Generating some derived column values automatically
Enforcing referential integrity
Event logging and storing information on table access
Auditing
Synchronous replication of tables
Imposing security authorizations
Preventing invalid transactions
Types of Triggers in Oracle
Triggers can be classified based on the following parameters.
Classification based on the timing
BEFORE Trigger: It fires before the specified event has occurred.
AFTER Trigger: It fires after the specified event has occurred.
INSTEAD OF Trigger: A special type. You will learn more about the further topics. (only for DML )
Classification based on the level
STATEMENT level Trigger: It fires one time for the specified event statement.
ROW level Trigger: It fires for each record that got affected in the specified event. (only for DML)
Classification based on the Event
DML Trigger: It fires when the DML event is specified (INSERT/UPDATE/DELETE)
DDL Trigger: It fires when the DDL event is specified (CREATE/ALTER)
DATABASE Trigger: It fires when the database event is specified (LOGON/LOGOFF/STARTUP/SHUTDOWN)
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