SQL269热题难！
查询每个日期新用户的次日留存率，1个表是新用户第一次登录min(date)，第2个表是同一个用户在第二天登录
代码如下：
select l.date, ifnull(round(count(distinct l2.user_id)/count(l1.user_id),3),0)p from login l left join login l1 on l1.id = l.id
and (l1.user_id, l1.date) in
(
select user_id, min(date)over(partition by user_id) from login
)
left join login l2 on l1.user_id = l2.user_id and l1.date = l2.date - 1
group by l.date
order by l.date ASC
#笔试#
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