题解 | #每份试卷每月作答数和截止当月的作答总数。#

with t1 as (
select exam_id,
date_format(start_time,'%Y%m') as start_month,
count(start_time) as month_cnt
FROM exam_record
group by exam_id,start_month
)
select *,sum(month_cnt) over(partition by exam_id order by start_month)
from t1