MERGE UPDATE

MERGE INTO Movie_Ratings M
USING (SELECT 1 AS mid, 3 AS aid, 8 AS rating FROM dual) N
ON (M.mid = N.mid AND M.aid = N.aid)
WHEN MATCHED THEN UPDATE
SET M.rating = N.rating
WHEN NOT MATCHED THEN INSERT( mid, aid, rating)
VALUES(N.mid, N.aid, N.rating); (Syntax not verified.)