题解 | #68#
牛客每个人最近的登录日期(三)
http://www.nowcoder.com/practice/16d41af206cd4066a06a3a0aa585ad3d
解法：
select round(count(l.date)/count(a.sd),3) from (select user_id,DATE_ADD(min(date),INTERVAL 1 DAY) as sd from login group by user_id) a left join login l on a.user_id=l.user_id and a.sd=l.date
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