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 *,sum(month_cnt) over(partition by exam_id order by start_month) from (select distinct exam_id, date_format(start_time,'%Y%m') start_month, count(start_time) over(partition by exam_id,date_format(start_time,'%Y%m')) month_cnt from exam_record) t1
sum(month_cnt) over(partition by exam_id order by start_month) ：根据月份排序可以计算出开始到当前月份的累计和（不是很理解求助）
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