Question

我知道你可以使用窗口函数获得数据子集的平均值，总数，最小值和最大值。但是，有可能得到中位数，或第25个百分位而不是窗口函数的平均值吗？

换句话说，我如何重写这个以获得每个区域内的ID和第25或第50百分位销售数字而不是平均值？

SELECT id, avg(sales)
    OVER (PARTITION BY district) AS district_average
FROM t

Answer 1

您可以使用percentile_cont()或percentile_disc()：

将其写为聚合函数

select district, percentile_cont(0.25) within group (order by sales)
from t
group by district;

不幸的是，Postgres目前不支持这些作为窗口函数：

select id, percentile_cont(0.25) within group (order by sales) over (partition by district) 
from t;

因此，您可以使用join：

select t.*, p_25, p_75
from t join
     (select district,
             percentile_cont(0.25) within group (order by sales) as p_25,
             percentile_cont(0.75) within group (order by sales) as p_75
      from t
      group by district
     ) td
     on t.district = td.district

使用窗函数

1 个答案: