查找每组购买产品的前10％然后找到10％的平均值

Question

原谅我的英语。我不确定这在MySQL中是否可行。

我正在努力：

1. 找出每个groupid得分的前10％
2. 然后找到平均值 分数为10％by groupid

数据的示例子集：

Table name: points

groupid       score
group_001     13
group_001     12
group_001     10
group_001     12
...
group_002     12
group_002     16
group_002     19
group_002     20
group_002     12
group_002     13
...
group_003     29
group_003     21
group_003     18
...

...

这可能吗？提前谢谢。

Answer 1

你可以做到，但这有点棘手。 。 。变量是最简单的方法：

select group_id, avg(score)
from (select p.*,
             (@rn := if(@g = group_id, @rn + 1,
                        if(@g := group_id, 1, 1)
                       )
             ) as seqnum
      from points p cross join
           (select @rn := 0, @g := -1) params
      order by group_id, score desc
     ) p join
     (select group_id, count(*) as cnt
      from points
      group by group_id
     ) pp
     on pp.group_id = p.group_id
where (seqnum - 1) * 10 <= pp.cnt
group by group_id;