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 DISTINCT
exam_id,
DATE_FORMAT(start_time,'%Y%m') as start_month,
count(start_time) over(partition by exam_id,date_format(start_time,'%Y%m')) as month_cnt,
count(start_time) over(partition by exam_id order by date_format(start_time,'%Y%m')) as cum_exam_cnt
from exam_record
order by exam_id,start_month
