Trigger Exceptions

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An exception is a named error message that can be raised from a trigger or a stored procedure. Exceptions are created with CREATE EXCEPTION, modified with ALTER EXCEPTION, and removed from the database with DROP ­EXCEPTION. For more information about these statements, see Working with Stored Procedures.

When raised in a trigger, an exception returns an error message to the calling program and terminates the trigger, unless the exception is handled by a WHEN statement in the trigger. For more information on error handling with WHEN, see Working with Stored Procedures.

For example, a trigger that fires when the EMPLOYEE table is updated might compare the employee’s old salary and new salary, and raise an exception if the salary increase exceeds 50%. The exception could return an message such as:

New salary exceeds old by more than 50%. Cannot update record.
Important: Like procedures and triggers, exceptions are created and stored in a database, where they can be used by any procedure or trigger in the database. Exceptions must be created and committed before they can be used in ­triggers.

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