题解 | #计算用户的平均次日留存率#

select
    round(count(id2) / count(id),4)  avg_ret
from
    (
        select distinct device_id id,date 
        from
            question_practice_detail ) qpd
        left join (
            select distinct device_id id2,date
            from question_practice_detail
            ) q2 
        on qpd.id = q2.id2 and q2.date=date_add( qpd.date ,interval 1 day );