题解 | #2021年11月每天新用户的次日留存率#

 select
 a.firstday, round(count(b.uid)/count(a.uid),2) uv_rate
 from(
    (select
    uid, date(min(in_time)) firstday
    from tb_user_log
    group by uid) a
    left join 
    (select uid, date(in_time) utime from tb_user_log
    union
    select uid, date(out_time) utime from tb_user_log) b
    on a.uid = b.uid and datediff(utime,firstday) = 1
 )
    where date_format(a.firstday,'%Y-%m') = '2021-11'
    group by a.firstday

参考大佬思路，后续还需复习