-- Update 구문 --
UPDATE a x
   SET item = (SELECT new FROM c WHERE item = x.item)
 WHERE EXISTS (SELECT new FROM c WHERE item = x.item)
;
UPDATE b x
   SET item = (SELECT new FROM c WHERE item = x.item)
 WHERE EXISTS (SELECT new FROM c WHERE item = x.item)
;
UPDATE f x
   SET item = (SELECT new FROM c WHERE item = x.item)
 WHERE EXISTS (SELECT new FROM c WHERE item = x.item)
;

-- Merge 구문 --
MERGE INTO a x USING c ON (c.item = x.item) WHEN MATCHED THEN UPDATE SET item = new;
MERGE INTO b x USING c ON (c.item = x.item) WHEN MATCHED THEN UPDATE SET item = new;
MERGE INTO f x USING c ON (c.item = x.item) WHEN MATCHED THEN UPDATE SET item = new;

마농님 감사합니다~~^^