SQL中的条件最大值

Question

我必须在 SQL Server 中执行以下查询：

SELECT EmployeeID, 
       TotalQuantity AS TotalQty, 
       TotalSales, 
       MAX(CASE WHEN MonthNumber = MAX(MonthNumber)
           THEN TotalSales END) as RecentMonthSale
FROM vwSales 
GROUP BY EmployeeID, TotalQuantity , TotalSales

但是它给了我错误：

Cannot perform an aggregate function on an expression
containing an aggregate or a subquery.

输入视图如下：

EmployeeID    TotaSales MonthNumber
  1             4000      1
  1             6000      2
  2             8500      1
  2             6081      2 

期望的输出：

EmployeeID    TotalSale     RecentMonthSale
  1            10000            6000
  2            14581            6081
  3            11458            1012 

我想要在我的输出EmployeeID, TotalQuantity TotalSale RecentMonthSale中的以下列 My View 具有以下列EmployeeID TotalSale,TotalQuantity, MonthNumber。

Answer 1

此查询将显示您需要的输出，并且只会扫描表一次。

select EmployeeID, sum(TotalSales), sum(case when MaxMonth = 1 then TotalSales else 0 end) RecentMonthSales
from 
(
    select *, rank() over(order by MonthNumber desc) MaxMonth
    from
    (
        select EmployeeID, MonthNumber, sum(TotalSales) TotalSales
        from vwSales
        group by EmployeeID, MonthNumber
    ) tt
) tt
group by EmployeeID