WHERE Something IN（CASE WHEN 语句）？

Question

我想根据条件条件写一个“select子句”！ 我有错误：

Msg 512, Level 16, State 1, Line 2
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

我该如何修复它？
这是我的简化代码：

SELECT  UnitsAllocation.UnitID
        , OrganizationUnits.Title AS UnitTitle
        , 'Title' AS ExpenseTitle1
        , SUM(UnitsAllocationDetails1.ExpenseAmount1) AS ExpenseAmount1 
FROM    [bdg_UnitsAllocation] UnitsAllocation 
        LEFT OUTER JOIN (
          SELECT  UnitsAllocationDetails.UnitsAllocationID
                  , SUM(UnitsAllocationDetails.Amount) / 1 AS ExpenseAmount1  
          FROM    [bdg_UnitsAllocationDetails] UnitsAllocationDetails  
          WHERE   UnitsAllocationDetails.ExpenseID IN (
                    CASE 1 WHEN 1 
                    THEN ( SELECT Id FROM bdg_Expenses WHERE ParentId = 1 ) 
                    ELSE ( SELECT Id FROM bdg_Expenses WHERE Id = 1 )  
                    END
                  )  
          GROUP BY 
                  UnitsAllocationDetails.UnitsAllocationID
        ) UnitsAllocationDetails1 ON UnitsAllocationDetails1.UnitsAllocationID = UnitsAllocation.ID 
        LEFT OUTER JOIN [bdg_OrganizationUnits] OrganizationUnits ON UnitsAllocation.UnitID = OrganizationUnits.ID 
GROUP BY 
        UnitsAllocation.UnitID, OrganizationUnits.Title 

请查看“CASE”和“IN”语句。

Answer 1

为什么要使用案例？你就不能这样做吗

where (@Level = 1 and ExpenseId in (select id from bdg_expenses where parentid = 1)) or
      (@Level <> 1 and ExpenseId in (select id from bdg_expenses where id = 1))