Tracking data changes
Triggers offer an efficient means of maintaining an audit trail. You can define a trigger to activate in response to certain DELETE, INSERT, or UPDATE statements that change data.
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You can qualify a trigger by providing a list of column names when you define the trigger. The qualified trigger is activated only when one of the named columns is changed. A trigger that performs validation for changes that are made in an UPDATE operation must access column values both before and after the update. Transition variables (available only to row triggers) contain the column values of the row change that activated the trigger. The old column values and the column values from after the triggering operation are both available.