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 a.*, sum(a.month_cnt) over(partition by a.exam_id order by a.start_month) from ( select er.exam_id, date_format(er.start_time,'%Y%m') as start_month, count(1) as month_cnt from exam_record er group by er.exam_id,date_format(er.start_time,'%Y%m') ) a
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