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 start_month,
count(*) as month_cnt,
sum(count(*)) over (partition by exam_id order by date_format(start_time, '%Y%m')
rows between unbounded preceding and current row) as cum_exam_cnt
from exam_record
group by exam_id, date_format(start_time, '%Y%m')
order by exam_id, start_month;
