sqlserver isnull()，Count()，sum()，month(getdate()) 的用法

select c.PayForYear,c.DptID,c.ZongShu,c.HasPayShu,c.NoPayShu
--,d.DepName
 from (
    select PayForYear,DptID
        ,isnull(Count(PartyMemberID),0) as ZongShu
        ,isnull(sum(iHasPay),0) HasPayShu, 
        --isnull()：PartyMemberID为空返回逗号后面的0
        --Count():不同PartyMemberID的数目。
        --sum():字段的总数  值相加
         case when isnull(Count(PartyMemberID),0) =0 then 0 
        else isnull(isnull(Count(PartyMemberID),0) - isnull(sum(iHasPay),0),0) end
         NoPayShu
     from ( 
            select pm.PartyMemberID,pm.DptID,isnull(pfr.PayForYear, year(getdate())) PayForYear,
        case when pfr.PayForMonth is null    then 0 
                when pfr.PayForMonth = month(getdate()) then 1 --当前月份select month(getdate()) 
                else 0 end as iHasPay 
                from partyMember pm
         left join PartyFeeRecord pfr on  (pm.PartyMemberID = pfr.PartyMemberID and pfr.PayForMonth is not null  
          and pfr.PayForMonth = month(getdate()) and isnull(pfr.PayForYear, year(getdate())) = year(getdate())) 
          ) b group by PayForYear,DptID 
   ) c 
   left join Department d on (c.DptID = d.DptID and IsTripAndKH =1 
   ) where c.NoPayShu >0 and d.[Path] like '%P10010012%'

总结：

1：--isnull()：PartyMemberID为空返回逗号后面的0；
2： --Count():不同PartyMemberID的数目。；
3：　　　　  --sum():字段的总数  值相加；
4：--month(getdate())； select month(getdate()) 得出当前月份