Percentile_disc获取中位数 - 我不想使用AVG，MIN，SUM，MAX

Question

这是我计算中位数的代码：

select distinct srt.Name,

    cast(sum(sr.price) as int) as AvgCost,cast(sum(sr.cost) as int) as 

    AvgTransCost,cast(avg(sr.TotalTimeSpent) as int) as TotalTimeSpent,

    percentile_disc(.5) WITHIN GROUP(ORDER BY avg(sr.price)) OVER(PARTITION BY srt.Name)    AS MedianSpend

在这一行：

percentile_disc(.5) WITHIN GROUP(ORDER BY avg(sr.price)) OVER(PARTITION BY srt.Name)    AS MedianSpend

我无法将其更改为：

(ORDER BY (sr.price))

如果我尝试在没有AVG infront（sr.price）的情况下运行代码，我会收到此错误：

http://i.stack.imgur.com/2jfS0.jpg

如何在不添加AVG，SUM，MIN，MAX之前运行它（sr.price）??