题解 | #每篇文章同一时刻最大在看人数#

• 对于同样一个类型的字段，可以采用编码+联立的方式来求取同样一个时间在线的人数
• 对于同时进出的，要先统计进的，再统计出的

select artical_id, max(user_cnt) from (
select artical_id, t,
sum(diff) over(partition by artical_id order by t asc, diff desc) user_cnt
from (
select artical_id artical_id, in_time t, 1 diff from tb_user_log 
where artical_id != 0 
union all 
select artical_id artical_id, out_time t, -1 diff from tb_user_log
where artical_id != 0 ) t1
) t2
group by 1
order by 2 desc