题解 | #每份试卷每月作答数和截止当月的作答总数。#

select t1.exam_id,t1.month_date,t1.cnt,sum(t1.cnt) over(partition by 
                                                       t1.exam_id 
                                                       order by t1.month_date asc) as cum_exam_cnt 
                                                       from (
select distinct exam_id,date_format(start_time,'%Y%m') as month_date,
count(start_time)
over(partition by exam_id,date_format(start_time,'%Y%m')) as cnt 
from exam_record ) t1