sql - 如何将 NULLIF 与聚合函数一起使用

Question

我正在使用 SQL Management Studio 2012。我收到“除以零错误”错误。我知道这需要使用 NULLIF 但我不确定如何在我的查询中使用它。

这是我的查询

select 
    Ward,
    LocalAuthority,
    Fiscal,
    DR,

    cast(DR*100.0 /SUM(DR) OVER (
        partition by localauthority, fiscal
        order by fiscal asc) as Decimal (10,2)) as [DR%]
from (
    select  
        Fiscal,
        LocalAuthority,
        Ward,
        sum(case when code = 'DR' then 1 else 0 end) as DR
    from [dbo].[Table]
    where datetimeofcall >= '2014-04-01' 
    group by
        ward,
        localauthority,f
        fiscal
) as A

我实际上已经问过这个问题，之前有人回答得很好，但是没有 OVER() 和 SUM 聚合函数，我对语法感到困惑。我一直在尝试以下的各种含义，但没有成功。

cast(DR*100.0 /NULLIF(SUM(DR,0),1) OVER(partition by localauthority,fiscal order by fiscal asc) as Decimal (10,2)) as [DR%]

Answer 1

用于Case Expression识别前面的 0

SELECT Ward, LocalAuthority, Fiscal, DR,
CASE WHEN SUM(DR) OVER(PARTITION BY localauthority, fiscal ORDER BY fiscal asc) = 0 THEN 0 ELSE CAST(DR*100.0 / SUM(DR) OVER(PARTITION BY  localauthority,fiscal ORDER BY fiscal) AS Decimal (10,2)) END AS [DR%]
FROM (
      SELECT Fiscal, LocalAuthority, Ward, SUM(CASE WHEN code = 'DR' THEN 1 ELSE 0 END) AS DR
      FROM [dbo].[Table]
      WHERE datetimeofcall >='2014-04-01' 
      GROUP BY ward, localauthority, fiscal
     ) AS A