题目：现在运营想要查看用户在某天刷题后第二天还会再来刷题的留存率。请你取出相应数据。 示例：question_practice_detail id device_id question_id result date 1 2138 111 wrong 2021-05-03 2 3214 112 wrong 2021-05-09 3 3214 113 wrong 2021-06-15 4 6543 111 right 2021-08-13 5 2315 115 right 2021-08-13 6 2315 116 right 2021-08-14 7 2315 117 wrong 2021-08-15 8 3214 112 wrong 2021-05-09 9 3214 113 wrong 2021-08-15 10 6543 111 right 2021-08-13 11 2315 115 right 2021-08-13 12 2315 116 right 2021-08-14 13 2315 117 wrong 2021-08-15 14 3214 112 wrong 2021-08-16 15 3214 113 wrong 2021-08-18 16 6543 111 right 2021-08-13 根据示例，你的查询应返回以下结果： avg_ret 0.3000
示例1

输入

drop table if  exists `question_practice_detail`;
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
);

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');

输出

avg_ret
0.3000
加载中...