To update data from other db in oracle

UPDATE TABLEA A SET (COLA, COLB)=(SELECT B.COLA, B.COLB FROM TABLEB B WHERE B.COL1=A.COL1 AND B.COL2=A.COL2 AND B.COL3='XXX') WHERE EXISTS (SELECT 'Z' FROM TABLEB B WHERE B.COL1=A.COL1 AND B.COL2=A.COL2 AND B.COL3='XXX') AND A.COL3='YYY';