题解 | #计算用户的平均次日留存率#

select round(count(q2.device_id)/count(q1.device_id),4)
as avg_ret
from (
    (select 
    distinct device_id,
    date
    from question_practice_detail as qpd1) as q1 
    left join
    (
        select distinct device_id,
        date 
        from question_practice_detail as qpd2
    ) as q2
    on q1.device_id = q2.device_id
    and datediff(q2.date,q1.date)=1
)