SQL使用開窗函數與CTE查詢每個月銷售額的前幾名

WITH tagTab AS(
SELECT YearMonth, 
pm=RANK() OVER(PARTITION BY YearMonth ORDER BY amount DESC) 
FROM SaleTab
)
SELECT * FROM tagTab WHERE pm<=5

　開窗函數：

http://technet.microsoft.com/zh-cn/library/ms189461(v=sql.105).aspx