题解 | 先升序再降序，可以排除同时间点进出｜每篇文章同一时刻最大在看人数

with raw as(
select
id,
uid,
artical_id,
in_time as time,
1 as tag
from tb_user_log
where artical_id != 0
union
select
id,
uid,
artical_id,
out_time as time,
-1 as tag
from tb_user_log
where artical_id != 0
)

select 
artical_id,
max(maxnum) as max_uv

from
    (
    select
    artical_id,
    tag,
    sum(tag)over(partition by artical_id order by time asc,tag desc) as maxnum
    from  raw


    )t
group by 1
order by max_uv desc