题解 | #每篇文章同一时刻最大在看人数#

select artical_id,max(cnt) as max_uv
from (
    select t2.uid,t2.artical_id,count(distinct t1.uid) cnt
from tb_user_log t1,tb_user_log t2
where t1.artical_id = t2.artical_id
and t1.in_time <=t2.out_time
and t1.out_time >= t2.out_time
and t1.artical_id <> 0
group by t2.uid,t2.artical_id
)c
group by artical_id
order by max_uv desc

常规思路，两表连接，取进入时间早于本人，退出时间晚于本人，

为什么不是 u1.in_time <= u2.in_time and u1.out_time > u2.in_time？主要是文章是取同一时刻最大在线人数