如何求和我数据库表中的最后15行？

Question

我有一个Sales表，有以下栏目：

• 雇员
• 量
• 日期

现在我想SUM了最后15行，所以我目前在做：

SELECT TOP 15 SUM(amount) FROM Sales ORDER BY [Date] DESC 

但我明显得到15行，有没有办法我可以总结它，而不必循环和SUM在客户端？

Answer 1

SELECT 
    SUM (Amount) 
FROM 
    (SELECT TOP 15 amount FROM Sales ORDER BY [Date] DESC) foo 

Answer 2

SELECT Sum(amount) 
FROM 
(
    SELECT Top 15 amount FROM Sales ORDER BY [Date] Desc 
) as bar