题目:现在运营想要查看用户在某天刷题后第二天还会再来刷题的平均概率。
select count(date2)/count(date) avg_ret from (select distinct qpd.device_id,qpd.date,qpd2.date as date2 from question_practice_detail qpd left join(select distinct device_id,date from question_practice_detail) as qpd2 on qpd.device_id=qpd2.device_id and date_add(qpd.date,interval 1 day)=qpd2.date) as dateqpd;