MERGE Into

 MERGE INTO CS_CL_DOME_IMG_PRT X
      USING (SELECT A.OID,
                    A.G_NO,
                    C.G_CODE,
                    C.G_NAME                 
               FROM A) Z
      ON (X.CL_OID = Z.OID AND X.G_NO = Z.G_NO)
      WHEN MATCHED THEN
        UPDATE
           SET X.HS_CODE     = Z.G_CODE,
               X.G_NAME      = Z.G_NAME,
               X.G_MODEL     = Z.ELEMENT             
      WHEN NOT MATCHED THEN
        INSERT
          (CL_OID,
           G_NO,
           HS_CODE,
           G_NAME,
           G_MODEL)
        VALUES
          (Z.OID,
           Z.G_NO,
           Z.G_CODE,
           Z.G_NAME,
           Z.ELEMENT);
           COMMIT;