题解 | #每份试卷每月作答数和截止当月的作答总数。#
每份试卷每月作答数和截止当月的作答总数。
https://www.nowcoder.com/practice/5f1cbe74c682485aa73e4c2b30f04a62
select exam_id,
start_month,
month_cnt,
sum(month_cnt)over(partition by exam_id
order by start_month) cum_exam_cnt
# 窗口函数，按exam_id分组，按start_month排序后求和至当前月之前的所有作答数
from
(select exam_id,
date_format(start_time,'%Y%m') start_month,
count(start_time) month_cnt
from exam_record
group by date_format(start_time,'%Y%m'),exam_id
) temp
start_month,
month_cnt,
sum(month_cnt)over(partition by exam_id
order by start_month) cum_exam_cnt
# 窗口函数，按exam_id分组，按start_month排序后求和至当前月之前的所有作答数
from
(select exam_id,
date_format(start_time,'%Y%m') start_month,
count(start_time) month_cnt
from exam_record
group by date_format(start_time,'%Y%m'),exam_id
) temp
查看30道真题和解析