中值：若总数为奇数，则中数为中间那个，若为偶数，则为中间两个平均 WITH RN AS(
SELECT CONVERT(VARCHAR(10),a.OrderDate,120) OrderDate,amount,
ROW_NUMBER () OVER ( PARTITION BY CONVERT(VARCHAR(10),a.OrderDate,120)  ORDER BY a.Amount,a.id) rx,
ROW_NUMBER () OVER ( PARTITION BY CONVERT(VARCHAR(10),a.OrderDate,120)  ORDER BY a.Amount DESC,a.id DESC  ) rl
FROM bdOrder a(NOLOCK)WHERE a.OrderDate >='2011-05-01' )
注：正序与倒序排，因为Amount值相同的情况，故要加id决定决胜因子。