题解 | #每份试卷每月作答数和截止当月的作答总数。#

with temp as (select exam_id
                   , date_format(start_time, '%Y%m') start_month
                   , count(1) as                     month_cnt
              from exam_record
              group by exam_id, start_month)
select exam_id
     , start_month
     , month_cnt
     , sum(month_cnt) over (partition by exam_id order by start_month) as cum_exam_cnt
from temp;