SELECT uid, CASE WHEN level is null THEN 0 ELSE level END AS level, CASE WHEN mileage is null THEN 0 ELSE mileage END AS mileage, CASE WHEN complaint_cnt is null THEN 0 ELSE complaint_cnt END AS complaint_cnt FROM( SELECT A.uid AS uid, level ,mileage, complaint_cnt FROM A LEFT JOIN B ON A.uid = B.UID LEFT JOIN C ON A.uid=C.UID ) j ;