题解 | #每篇文章同一时刻最大在看人数#

自己写的错误案例： 所有情况都暂时考虑到，但是忽略了如果处于同时刻则先加一后减一的情况，导致在sql里和自测答案正确，提交不通过……所有这个条件应该放在哪呢~

select artical_id,
	max(在读人数) as 最大同时在读人数 
	from
		(select  *,
			sum(动作标识) over(partition by artical_id order by 时间标识) as 在读人数 from
		((select artical_id,in_time as 时间标识,1 as 动作标识 from tb_user_log where artical_id <> 0)
		union all 
		(select artical_id,out_time as 时间标识,-1 as 动作标识 from tb_user_log where artical_id <> 0)) a) b
	group by artical_id
	order by 最大同时在读人数 desc;