Sql 如何在透视表中使用SUM（不能在聚合函数中使用CAST）

我正在使用以下透视查询：

    select UserId_Fk,Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
      from CheckInCheckOut

    PIVOT
    (

     SUM(CAST(CountHours as decimal(18,2))) 
     FOR Day
     IN([Sunday],[Monday],[Tuesday],[Wednesday],[Thursday],[Friday],[Saturday])

    )
   as PivotTable

   Table[CheckInCheckOut]     

 CheckInCheckOutId  int 
    UserId_Fk       int 
  CountHours    nvarchar(50)    
         Day    nvarchar(50)    

我在这里使用SUM有点不对劲。我试过了

   select SUM(CAST(CountHours as decimal(18,2))) from CheckInCheckOut

---

这给了我正确的结果，但我不能在Pivot表中使用相同的结果。

因为我没有使用sql server/Pivot，这只是一个猜测，但其中是否应该是group by子句？即

...
as PivotTable
group by UserId_Fk, ...

---

在进行数据透视查询之前，请尝试转换数据

  select UserId_Fk,Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
      from    (Select UserId_Fk,CAST(CountHours as decimal(18,2))as CountHours,[Day]
   from CheckInCheckOut) as convertedtable

    PIVOT
    (

     SUM(CountHours) 
     FOR Day
     IN([Sunday],[Monday],[Tuesday],[Wednesday],[Thursday],[Friday],[Saturday])

    )
   as PivotTable