【SQL牛客在线编程答案】 【01】 select device_id, gender, age, university from user_profile; [次日平均留存率] select count(distinct b.device_id,b.date)/count(distinct a.device_id,a.date) as avg_ret from question_practice_detail as a left join question_practice_detail as b on a.device_id = b.device_id and datediff(b....
