SQL Server：如何获取Top（n）和Bottom（n）记录的平均值

Question

我有一张分数表：

Student ¦ Score
  A     ¦ 23.5
  B     ¦ 34.9

如何获得ALL的平均值，前15％和后15％这样：

Average ¦ top15Avg ¦ bottom15Avg

感谢。

Answer 1

首先计算15％的行数。 然后你可以做这样的选择和平均值：

declare @pct int, @all float, @top float, @bottom float
select  @pct = 0.15 * COUNT(*) from Students

select @all = AVG(score) from Students
select @top = AVG(score) from (select top (@pct) score from Students order by score desc)
select @bottom = AVG(score) as 'bottom15Avg' from (select top (@pct) score from Students order by score asc)
select @all as 'Average', @top as 'top15Avg', @bottom  as 'bottom15Avg'