题解 | #每份试卷每月作答数和截止当月的作答总数。#
每份试卷每月作答数和截止当月的作答总数。
https://www.nowcoder.com/practice/5f1cbe74c682485aa73e4c2b30f04a62
select exam_id, date_format(start_time,"%Y%m") as month, count(id), sum(count(id))over(partition by exam_id order by date_format(start_time,"%Y%m") ) from exam_record group by exam_id,month