如何当sum() 返空时,显示为0呢?

Question

SELECT  danglist.SL ,
           danglist.DW ,
           danglist.DKSN ,
           danglist.paper ,
           danglist.JJ ,
           danglist.long ,
           danglist.wide ,
           danglist.high ,
           danglist.back_high ,
           danglist.JD ,
           danglist.JC ,
           danglist.dh ,
           danglist.DJ ,
           danglist.HQ ,
           danglist.ID ,
           danglist.PONO,
           眒堤諳杅 =
          (select isNull(sum(outsn),0) from qhd_list where qhd_list.ddh =danglist.ID) 
        FROM danglist      
        WHERE ( danglist.dh = :ls_dh )