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) AS avg_ret
FROM question_practice_detail AS t1
LEFT JOIN question_practice_detail AS t2
ON t1.device_id=t2.device_id  AND TIMESTAMPDIFF(DAY,t1.date,t2.date)=1;