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。     
已邀请:
        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     

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