Offset function and windowing function

Case study

Calculate the average next day retention rate of users

Create table statement

drop table if exists `user_profile`;
drop table if  exists `question_practice_detail`;
drop table if  exists `question_detail`;
CREATE TABLE `user_profile` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`gender` varchar(14) NOT NULL,
`age` int ,
`university` varchar(32) NOT NULL,
`gpa` float,
`active_days_within_30` int ,
`question_cnt` int ,
`answer_cnt` int 
);
CREATE TABLE `question_practice_detail` (
`id` int NOT NULL,
`device_id` int NOT NULL,
`question_id`int NOT NULL,
`result` varchar(32) NOT NULL,
`date` date NOT NULL
);
CREATE TABLE `question_detail` (
`id` int NOT NULL,
`question_id`int NOT NULL,
`difficult_level` varchar(32) NOT NULL
);

INSERT INTO user_profile VALUES(1,2138,'male',21,' Peking University, ',3.4,7,2,12);
INSERT INTO user_profile VALUES(2,3214,'male',null,' Fudan University ',4.0,15,5,25);
INSERT INTO user_profile VALUES(3,6543,'female',20,' Peking University, ',3.2,12,3,30);
INSERT INTO user_profile VALUES(4,2315,'female',23,' Zhejiang University ',3.6,5,1,2);
INSERT INTO user_profile VALUES(5,5432,'male',25,' Shandong University ',3.8,20,15,70);
INSERT INTO user_profile VALUES(6,2131,'male',28,' Shandong University ',3.3,15,7,13);
INSERT INTO user_profile VALUES(7,4321,'male',28,' Fudan University ',3.6,9,6,52);
INSERT INTO question_practice_detail VALUES(1,2138,111,'wrong','2021-05-03');
INSERT INTO question_practice_detail VALUES(2,3214,112,'wrong','2021-05-09');
INSERT INTO question_practice_detail VALUES(3,3214,113,'wrong','2021-06-15');
INSERT INTO question_practice_detail VALUES(4,6543,111,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(5,2315,115,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(6,2315,116,'right','2021-08-14');
INSERT INTO question_practice_detail VALUES(7,2315,117,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(8,3214,112,'wrong','2021-05-09');
INSERT INTO question_practice_detail VALUES(9,3214,113,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(10,6543,111,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(11,2315,115,'right','2021-08-13');
INSERT INTO question_practice_detail VALUES(12,2315,116,'right','2021-08-14');
INSERT INTO question_practice_detail VALUES(13,2315,117,'wrong','2021-08-15');
INSERT INTO question_practice_detail VALUES(14,3214,112,'wrong','2021-08-16');
INSERT INTO question_practice_detail VALUES(15,3214,113,'wrong','2021-08-18');
INSERT INTO question_practice_detail VALUES(16,6543,111,'right','2021-08-13');
INSERT INTO question_detail VALUES(1,111,'hard');
INSERT INTO question_detail VALUES(2,112,'medium');
INSERT INTO question_detail VALUES(3,113,'easy');
INSERT INTO question_detail VALUES(4,115,'easy');
INSERT INTO question_detail VALUES(5,116,'medium');
INSERT INTO question_detail VALUES(6,117,'easy');

select avg(if(DATEDIFF(date2,date1)=1,1,0)) as avg_ret from
(select date as date1,lead(date,1) over(partition by device_id order by date) as date2 from 
(select DISTINCT device_id,date from question_practice_detail) as unique_date) as aa

A few problems to pay attention to ：
1、if function
2、lead function ,lead（ Column or function , How many lines in the future do not fill in the default 1, The default value defaults to null）
3、distinct Act on multiple columns , In fact, according to multiple columns to remove the heavy ;
4、 Subqueries use aliases