题解 | 每份试卷每月作答数和截止当月的作答总数。

# 每份试卷每月的作答数 和累计总作答数

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