Sql164 next day retention rate of new users per day in November 2021

# The date each user was first active , surface 1
select uid,date(min(in_time))
from tb_user_log
group by uid

# The date each user is active , surface 2
select uid,date(in_time)as dt
from tb_user_log
union
select uid,date(out_time)as dt
from tb_user_log
order by uid

# Check the current day 、 The activity of users the next day , The next day uid If it is blank, it means that it is not retained the next day 
# Return four columns ： Date of the day ,uid, The next day ,uid
# surface 1 Left link table 2, The condition is that the date is different 1 God 
1、timestampdiff( Company , Starting time , End time )
 Company ：sencond,minute,hour,day,week,month,year
2、from...join...on+ Conditions 
select *
from
    (select uid,date(min(in_time))as dt
    from tb_user_log
    group by uid)as a
left join
    (select uid,date(in_time)as dt
    from tb_user_log
    union
    select uid,date(out_time)as dt
    from tb_user_log
    order by uid)as b
on a.uid=b.uid
and timestampdiff(day,a.dt,b.dt)=1

# Calculate secondary retention 
1、round(a,3):a Keep three decimal places 
select a.dt
    ,round(count(b.uid)/count(a.uid),2)as uv_left_rate
from
    (select uid,date(min(in_time))as dt
    from tb_user_log
    group by uid)as a
left join
    (select uid,date(in_time)as dt
    from tb_user_log
    union
    select uid,date(out_time)as dt
    from tb_user_log
    order by uid)as b
on a.uid=b.uid
and timestampdiff(day,a.dt,b.dt)=1
where a.dt like"2021-11%" # Limit the time range 
group by a.dt