题解 | #计算用户的平均次日留存率#

select
    count(distinct T2.device_id, T2.date) / count(distinct T1.device_id, T1.date)
from
    question_practice_detail as T1
    left join question_practice_detail as T2 on T1.device_id = T2.device_id
    and datediff (T2.date, T1.date) = 1;