[英]How to find median by attribute with Postgres window functions?
I use PostgreSQL and have records like this on groups of people: 我使用PostgreSQL并在一群人上有这样的记录:
name | people | indicator
--------+--------+-----------
group 1 | 1000 | 1
group 2 | 100 | 2
group 3 | 2000 | 3
I need to find the indicator
for the median person . 我需要找到中位人士的
indicator
。 The result should be 结果应该是
group 3 | 2000 | 3
If I do 如果我做
select median(name) over (order by indicator) from table1
It will be group 2
. 这将是
group 2
。
Not sure if I can select this with a window function. 不知道我是否可以使用窗口功能选择它。
Generating 1000/2000 rows per record seems impractical, because I have millions of people in the records. 每条记录生成1000/2000行似乎是不切实际的,因为记录中有数百万人。
Find the first cumulative sum of people greater than the median of total sum: 查找大于总和中位数的人的第一个累积总和:
with the_data(name, people, indicator) as (
values
('group 1', 1000, 1),
('group 2', 100, 2),
('group 3', 2000, 3)
)
select name, people, indicator
from (
select *, sum(people) over (order by name)
from the_data
cross join (select sum(people)/2 median from the_data) s
) s
where sum > median
order by name
limit 1;
name | people | indicator
---------+--------+-----------
group 3 | 2000 | 3
(1 row)
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