sql server case when 判断为空

代码如下

 select
        distinct G.* 
        ,(select BUSINESS_NAME from BusinessInfo where BusinessInfo.BUSINESS_BID=G.G_BUSINESS_ID) as BUSINESS_NAME
        ,(select sum(StockGNum) from StockDetail where StockDetail.StockGID =G.G_ID) as StockGNum
        ,(select sum(StockRemovalGNum) from StockRemovalDetail where StockRemovalDetail.StockRemovalGID =G.G_ID) as StockRemovalGNum
        ,T.COMMUNITYID
        ,case when GNumber is null then 0 else DA.GNumber end as GNumber  -- 判断为空
    from
        B_GoodsInfo G left join  B_Goods_Type T on G.G_BUSINESS_ID = T.T_BUSINESS_ID left join BusinessInfo B on G.G_BUSINESS_ID = B.BUSINESS_BID
        left join (select * from  DiningCarApplyDetail where ApplyForDate = CONVERT(varchar(100), GETDATE(), 23)) DA on DA.GID=G.G_ID
    where
      T.COMMUNITYID = '43450BD834E54247A187DD0186E96240'
      and B.BUSINESS_Type='001'