题目

建表语句

drop table if exists examination_info;
CREATE TABLE examination_info (
    id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
    exam_id int UNIQUE NOT NULL COMMENT '试卷ID',
    tag varchar(32) COMMENT '类别标签',
    difficulty varchar(8) COMMENT '难度',
    duration int NOT NULL COMMENT '时长',
    release_time datetime COMMENT '发布时间'
)CHARACTER SET utf8 COLLATE utf8_general_ci;
drop table if exists exam_record;
CREATE TABLE  exam_record (
    id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
    uid int NOT NULL COMMENT '用户ID',
    exam_id int NOT NULL COMMENT '试卷ID',
    start_time datetime NOT NULL COMMENT '开始时间',
    submit_time datetime COMMENT '提交时间',
    score tinyint COMMENT '得分'
)CHARACTER SET utf8 COLLATE utf8_general_ci;
INSERT INTO examination_info(exam_id,tag,difficulty,duration,release_time) VALUES
  (9001, 'SQL', 'hard', 60, '2020-01-01 10:00:00'),
  (9002, 'SQL', 'easy', 60, '2020-02-01 10:00:00'),
  (9003, '算法', 'medium', 80, '2020-08-02 10:00:00');
INSERT INTO exam_record(uid,exam_id,start_time,submit_time,score) VALUES
(1001, 9001, '2021-07-02 09:01:01', '2021-07-02 09:21:01', 80),
(1002, 9001, '2021-09-05 19:01:01', '2021-09-05 19:40:01', 81),
(1002, 9002, '2021-09-02 12:01:01', null, null),
(1002, 9003, '2021-09-01 12:01:01', null, null),
(1002, 9001, '2021-07-02 19:01:01', '2021-07-02 19:30:01', 82),
(1002, 9002, '2021-07-05 18:01:01', '2021-07-05 18:59:02', 90),
(1003, 9002, '2021-07-06 12:01:01', null, null),
(1003, 9003, '2021-09-07 10:01:01', '2021-09-07 10:31:01', 86),
(1004, 9003, '2021-09-06 12:01:01', null, null),
(1002, 9003, '2021-09-01 12:01:01', '2021-09-01 12:31:01', 81),
(1005, 9001, '2021-09-01 12:01:01', '2021-09-01 12:31:01', 88),
(1005, 9002, '2021-09-01 12:01:01', '2021-09-01 12:31:01', 88),
(1006, 9002, '2021-09-02 12:11:01', '2021-09-02 12:31:01', 89);

解题思路

题意提炼
统计2021年每个【未完成试卷作答数大于1】的【有效用户】的数据（有效用户指完成试卷作答数至少为1且未完成数小于5），输出用户ID、未完成试卷作答数、完成试卷作答数、作答过的试卷tag集合，按未完成试卷数量由多到少排序

问题分解

关联作答记录和试卷信息：left join examination_info on using(exam_id)；（题中exam_record中的exam_id在examination_info均存在，所以用left join和inner join效果一样）
筛选2021年的记录：where year(start_time)=2021
获取各用户的tag,start_time及未完成标记和已完成标记，如果该作答记录交卷了则已完成标记为1，未完成标记为0，否则相反：if(submit_time is null, 1, null) as incomplete
按用户分组：group by uid
统计未完成试卷作答数和已完成试卷作答数：count(incomplete) as incomplete_cnt
统计作答过的tag集合：
- 对于每条作答tag，用:连接日期和tag：concat_ws(':', date(start_time), tag)
- 对于一个人（组内）的多条作答，用;连接去重后的作答记录：group_concat(distinct concat_ws(':', date(start_time), tag) SEPARATOR ';')
筛选未完成试卷作答数大于1的有效用户：having complete_cnt >= 1 and incomplete_cnt BETWEEN 2 and 4
- 完成试卷作答数至少为1：complete_cnt >= 1
- 未完成数小于5：incomplete_cnt < 5
- 未完成试卷作答数大于1：incomplete_cnt > 1

SQL代码

SELECT uid, count(incomplete) as incomplete_cnt,
    count(complete) as complete_cnt,
    group_concat(distinct concat_ws(':', date(start_time), tag) SEPARATOR ';') as detail
from (
    SELECT uid, tag, start_time,
        if(submit_time is null, 1, null) as incomplete,
        if(submit_time is null, null, 1) as complete
    from exam_record
    left join examination_info using(exam_id)
    where year(start_time)=2021
) as exam_complete_rec
group by uid
having complete_cnt >= 1 and incomplete_cnt BETWEEN 2 and 4
order by incomplete_cnt DESC

LeetCode

未完成试卷数大于1的有效用户

题目

解题思路

SQL代码