题解 | #每份试卷每月作答数和截止当月的作答总数。#一个开窗函数搞定
每份试卷每月作答数和截止当月的作答总数。
http://www.nowcoder.com/practice/5f1cbe74c682485aa73e4c2b30f04a62
select exam_id,start_month,month_cnt, sum(month_cnt)over(partition by exam_id order by start_month) as cum_exam_cnt from ( select exam_id,date_format(start_time,'%Y%m') as start_month, count(1) as month_cnt from exam_record group by exam_id,date_format(start_time,'%Y%m') ) t
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