如何在 Postgres 中使用具有多个分位数的percentile_conts

Question

我目前有一个查询，其工作方式如下：

select AVG(t2 - t1) as delay,
       percentile_cont(0.25) within group (order by (t2 - t1)) as q25,
       percentile_cont(0.5) within group (order by (t2 - t1)) as median,
       percentile_cont(0.75) within group (order by (t2 - t1)) as q75,
       p.bool1,
       p.cat1
from people p
group by p.bool1, p.cat1
order by p.cat1,p.bool1

但是，我在 postgres 函数聚合页面上阅读： https://www.postgresql.org/docs/9.4/functions-aggregate.html

我应该能够指定多个分位数：

percentile_cont(fractions) WITHIN GROUP (ORDER BY sort_expression)  double precision[]  double precision or interval    array of sort expression's type     multiple continuous percentile: returns an array of results matching the shape of the fractions parameter, with each non-null element replaced by the value corresponding to that percentile

我想使用它，这样我就不会重新计算每个分位数的 t2 - t1 。获取多个分位数的正确语法是什么？我需要子查询吗？

Answer 1

我想使用它，这样我就不会重新计算每个分位数的 t2 - t1

横向连接在这种情况下可能会有所帮助：

select AVG(t2 - t1) as delay,
       percentile_cont(0.25) within group (order by s.col) as q25,
       percentile_cont(0.5) within group (order by s.col) as median,
       percentile_cont(0.75) within group (order by s.col) as q75,
       p.bool1,
       p.cat1
from people p
,LATERAL(SELECT t2 - t1 AS col) s
group by p.bool1, p.cat1
order by p.cat1,p.bool1;

相关：PostgreSQL：在同一查询中使用计算列

数组定义为：ARRAY[0.25, 0.5, 0.75] 或'{0.25, 0.5, 0.75}'::double precision[]

select AVG(t2 - t1) as delay,
   -- 1
   percentile_cont(ARRAY[0.25, 0.5, 0.75]) within group (order by (t2 - t1)) as q25,
   -- 2
   percentile_cont('{0.25, 0.5, 0.75}'::double precision[]) 
   within group (order by (t2 - t1)) as q
       p.bool1,
       p.cat1
from people p
group by p.bool1, p.cat1
order by p.cat1,p.bool1;

db<>小提琴演示

有没有一种简单的方法来内联指定每个结果百分位字段的名称，就像它们与 q25、q50、q75 等一样

WITH cte AS (
    select AVG(t2 - t1) as delay,
       percentile_cont(ARRAY[0.25, 0.5, 0.75]) within group (order by (t2 - t1)) as q,
           p.bool1,
           p.cat1
    from people p
    group by p.bool1, p.cat1
)
select cte.*, q[1] AS q25, q[2] AS q50, q[3] AS q75
from cte
order by cat1,bool1;

db<>小提琴演示2