CREATE or replace TRIGGER RATINGS_trigger BEFORE INSERT --RATINGSxx 
ON RATINGS FOR EACH ROW --RATINGSxx 
BEGIN --RATINGSxx 
IF :new.RATING_ID = 0 THEN --RATINGSxx 
select max(RATING_ID)+1 into :new.RATING_ID from RATINGS   ; --RATINGSxx 
END IF;--RATINGSxx 
END; --RATINGSxx