SQL中的条件最大值

如何解决SQL中的条件最大值

| 我必须在sql Server中进行以下查询：

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 

所需的输出：

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

我想在输出

EmployeeID,TotalQuantity TotalSale RecentMonthSale

中跟随以下列。我的视图在the5ѭ中具有下面的列。     

解决方法

        此查询将显示所需的输出，并且仅扫描表一次。

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

    ,        

SELECT
    vw.EmployeeID,SUM(vw.TotalSale) as Total,Recent.RecentMonthSale
FROM
    vwSales vw
    LEFT JOIN
    (
        SELECT
            _vw.EmployeeID,_vw.TotalSale as RecentMonthSale
        FROM
            vwSales _vw
        INNER JOIN
        (
            SELECT EmployeeID,MAX(MonthNumber) as MaxMonth
            FROM vwSales
            GROUP BY EmployeeID
        ) _a
        on _vw.EmployeeID = _a.EmployeeID
        and _vw.MonthNumber = _a.MaxMonth
    ) Recent
    on Recent.EmployeeID = vw.EmployeeID
GROUP BY
    vw.EmployeeID,Recent.RecentMonthSale

如果仅执行每个子查询并查看其结果，则应该对它的工作原理有所了解