Use exception-name to specify the name of an exception declared using a DECLARE statement at the beginning of the current compound statement.
The exception must correspond to a system-defined SQLSTATE or a user-defined SQLSTATE. User-defined SQLSTATE values must be
in the range 99000 to 99999.
The following compound statement declares and signals a user-defined exception. If you execute this example from Interactive
SQL, the message My exception signaled appears on the Messages tab in the Results area.
BEGIN
DECLARE myexception EXCEPTION
FOR SQLSTATE '99001';
SIGNAL myexception;
EXCEPTION
WHEN myexception THEN
MESSAGE 'My exception signaled'
TO CLIENT;
END