题解 | #计算用户的平均次日留存率#
计算用户的平均次日留存率
https://www.nowcoder.com/practice/126083961ae0415fbde061d7ebbde453
SELECT COUNT(distinct q2.device_id,q2.date)/count(DISTINCT q1.device_id,q1.date) as avg_ret from question_practice_detail as q1 left join question_practice_detail as q2 on q1.device_id=q2.device_id and DATEDIFF(q2.date,q1.date)=1
count(distinct a,b):若a或者b中有一个是null,则这行不参与计数
datediff(datepart,startdate,enddate):返回两个日期之间的时间差