题解 | #每份试卷每月作答数和截止当月的作答总数。#

# table exam_record 
# 每份试卷 每月作答数 
# 每份试卷 截止当月作答数 （累加） sum order by
# 根据示例可知只要有starttime 就算作答
with temp as (
    select exam_id,
        date_format(start_time, '%Y%m') time1
    from exam_record
)
select e.*,
    sum(e.month_cnt) over (partition by e.exam_id order by e.start_month) cum_exam_cnt
from(
    select exam_id, time1 start_month,
        count(*) month_cnt
    from temp
    group by exam_id, time1
) e
order by exam_id, start_month;