题解 | #牛客每个人最近的登录日期(四)#
牛客每个人最近的登录日期(四)
http://www.nowcoder.com/practice/e524dc7450234395aa21c75303a42b0a
第一步，找出所有日期
select distinct date from login
第二步， 找出所有第一次登陆的id和日期
select user_id, min(date) first_date from login
group by user_id
group by user_id
第三步，左连接2个表格并排序
select a.date, count(distinct b.user_id)
from (select distinct date from login) a
left JOIN
(select user_id, min(date) first_date from login
group by user_id) b
on a.date = b.first_date
group by a.date
order by a.date;
from (select distinct date from login) a
left JOIN
(select user_id, min(date) first_date from login
group by user_id) b
on a.date = b.first_date
group by a.date
order by a.date;
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