使用等级计算各种平均值

问题描述

我的数据看起来像这样

+------+--------+------+-------+
| year | month  | name | value |
+------+--------+------+-------+
| 2017 |      1 | John |   100 |
| 2017 |      2 | Doe  |   200 |
| 2017 |      3 | Jane |   300 |
|    . |      . | .    |     . |
| 2018 |      1 | John |   150 |
| 2018 |      2 | Doe  |   250 |
| 2018 |      3 | Jane |   350 |
+------+--------+------+-------+

我正在尝试计算每年和每月前2个名字的平均值。我可以使用下面的代码

select year,month,avg(sum_value) as avg_of_2
from (
    select year,name,sum(value) as sum_value,rank() over (partition by year,month order by sum(value) desc) as rnk
      from database.table_a
      group by year,name
      order by 1,2,4 desc
    ) tbl_for_2
where rnk <= 2 -- for top 2 values
group by 1,2
order by 1,2;

但是现在我想将平均值从前2个名称扩展到前5、10和50。有没有办法可以在不重复相同查询的情况下使用等级来实现？

我的最终结果将是

+------+-------+----------+----------+---------+
| year | month |  avg_2   |  avg_5   | avg_10  |
+------+-------+----------+----------+---------+
| 2017 |     1 | some_val | some_val | som_val |
| 2017 |     2 | some_val | some_val | som_val |
|   .. |       |          |          |         |
|   .. |       |          |          |         |
+------+-------+----------+----------+---------+

解决方法

没有办法返回动态列数，必须写所有列。只需在外部查询中使用过滤的聚合：

select year,month,AVG(sum_value)FILTER(WHERE rnk<=2) as avg_2,AVG(sum_value)FILTER(WHERE rnk<=5) as avg_5,AVG(sum_value)FILTER(WHERE rnk<=10) as avg_10,.................
  AVG(sum_value)FILTER(WHERE rnk<=100) as avg_100,... and so on
from (
    select year,name,sum(value) as sum_value,rank() over (partition by year,month order by sum(value) desc) as rnk
      from database.table_a
      group by year,name
    ) tbl
group by 1,2
order by 1,2;

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