CREATE OR REPLACE TRIGGER nachm_nicht_loeschen
BEFORE DELETE ON City
BEGIN
  IF SYSDATE
     BETWEEN to_date('12:00', 'HH24:MI')
         AND to_date('18:00', 'HH24:MI')
  THEN RAISE_APPLICATION_ERROR
         (-20101,'Unerlaubte Aktion');
  END IF;
END;
/
