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。
http://www.nowcoder.com/practice/5f1cbe74c682485aa73e4c2b30f04a62
select distinct
exam_id,date_format(start_time,'%Y%m') as m,
count(id) over(partition by exam_id, date_format(start_time,'%Y%m') ) as cnt_m,
count(id) over(partition by exam_id order by date_format(start_time,'%Y%m') )
as sum_cnt_m
from exam_record
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