题解 | #每篇文章同一时刻最大在看人数#

-- “同一时刻有进入有离开时，先记录增加后记录减少” ，进入+1，退出-1，可以使用sum窗口函数，对文章进行分组，然后先日期升序，再对人数进行降序排列
select artical_id,max(sum_cnt) as max_uv 
from (
select artical_id,sum(diff) over(partition by artical_id order by dt ,diff desc) as sum_cnt
from (
select uid ,artical_id,in_time dt ,1 diff
from tb_user_log 
where artical_id <> 0 

union all 
select uid ,artical_id,out_time dt ,-1 diff
from tb_user_log 
where artical_id <> 0 ) t1 ) t2 
group by artical_id 
order by max_uv desc