select a.dt,
round(count(b.dt)/count(a.dt),2) as uv_left_rate
from
(select uid,min(date(in_time)) as dt
from tb_user_log 
group by uid) a
left join 
(select uid, date(in_time) dt
from tb_user_log 
union
select uid, date(out_time) dt
from tb_user_log ) b
on a.uid=b.uid and
date_add(a.dt,interval 1 day)=b.dt
where year(a.dt)=2021 and month(a.dt)=11
group by a.dt
order by a.dt