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
# 1.思路：出现“截止当月”的关键词，应该要使用窗口函数的order by选项 # 2.求解 select exam_id, date_format(start_time, '%Y%m') start_month, count(*) month_cnt, sum(count(*))over(partition by exam_id order by date_format(start_time, '%Y%m')) cum_exam_cnt from exam_record group by exam_id, date_format(start_time, '%Y%m');
