Question

如何对我的Postgres表中按值排序的所有值的50％求和？

在表格中我有值1，2，3，4，5，6，我想得到按值DESC排序的半值之和。结果将是4 + 5 + 6 = 15

另外，我可能只想获得1/3的值，所以我会得到6 + 5 = 11

Postgres中的SQL是否可行？像

这样的东西

SELECT sum(value)
FROM (
       SELECT value
       FROM table
       ORDER BY value DESC
       LIMIT 50%
     ) subquery

Answer 1

我会使用row_number()和count()：

SELECT sum(value)
FROM (SELECT value, ROW_NUMBER() OVER (ORDER BY value) as seqnum,
             COUNT(*) OVER () as cnt
      FROM table
     ) subquery
WHERE seqnum <= cnt * 0.5;

Answer 2

percent_rank：

with t (value) as (values (1),(2),(3),(4),(5),(6))
select sum(value)
from (
    select value, percent_rank() over (order by value) as pr
    from t
) S
where pr > 0.5
;
 sum 
-----
  15

Answer 3

我提出了我的版本：

SELECT sum(value)
FROM (
       SELECT
         value,
         ntile(10)
         OVER (
           ORDER BY value DESC ) AS tile
       FROM t
     ) subquery
WHERE tile >= 10*0.5;

这对count of values < ntile's N不起作用，但最后我打算将其用于数千个值

如何在Postgres中总结n％的值

3 个答案: