sql - 在 SQL Server 中使用带有 SUM 函数的 CASE 语句

Question

我正在研究 SQL Server 2008 R2。我正在尝试计算总和。

这是我的查询

select  
  SUM(
    case 
      when sec.SecurityTypeID =  2 then SUM(quantity)*(sec.AnnualIncomeRate/100) 
      when sec.SecurityTypeID = 5 then 0 
      when sec.SecurityTypeID = 11 then SUM(quantity)*sec.AnnualIncomeRate    
      else SUM(quantity)*sec.AnnualIncomeRate   
    end
  ) AS ProjectedIncome 
from Transactions as t

当我执行它时，出现以下错误。

Msg 130, Level 15, State 1, Line 3
Cannot perform an aggregate function on an expression containing an aggregate or a sub query.

我知道我正在使用带有 case 子句的 sum 函数。但我需要用这个案例陈述求和。

Answer 1

确实；该 case 是每行，因为您没有 group； SUM(quantity) 在引用单行时基本上没有意义。如果这是整个集合的SUM，您将必须首先将其计算到一个变量中。否则，您需要考虑您希望将内部SUM应用于哪个组/分区。

举一个类似的例子:

这有效:

select 1 as [a], 2 as [b], 3 as [c]

这有效:

select case [a] when 1 then [b] else [c] end from (
  select 1 as [a], 2 as [b], 3 as [c]
) x

但这并不:

select case [a] when 1 then sum([b]) else [c] end from (
  select 1 as [a], 2 as [b], 3 as [c]
) x

同样，这有效:

select sum(case [a] when 1 then [b] else [c] end) from (
  select 1 as [a], 2 as [b], 3 as [c]
) x

但事实并非如此，给出了与您报告的相同的错误消息:

select sum(case [a] when 1 then sum([b]) else [c] end) from (
  select 1 as [a], 2 as [b], 3 as [c]
) x