Error Conditions and Exceptions in the Trigger Body

If a predefined or user-defined error condition or exception occurs during the execution of a trigger body, then all effects of the trigger body, as well as the triggering statement, are rolled back unless the error is trapped by an exception handler. Therefore, a trigger body can prevent the execution of the triggering statement by raising an exception. User-defined exceptions are commonly used in triggers that enforce complex security authorizations or integrity constraints. See "Creating a Trigger With an Exception Handler" and "Handling PL/SQL Errors".