题解 | #计算用户的平均次日留存率#

SELECT COUNT(distinct q2.device_id,q2.date)/COUNT(distinct q1.device_id,q1.date) as avg_ret
FROM question_practice_detail q1
LEFT  JOIN question_practice_detail q2
ON q1.device_id=q2.device_id and datediff(q1.date,q2.date)=1