现有试卷作答记录表exam_record（uid：用户ID, exam_id：试卷ID, start_time：开始作答时间, submit_time：交卷时间，没提交的话为NULL, score：得分），示例数据如下： id uid exam_id start_time submit_time score 1 1001 9001 2021-07-02 09:01:01 (NULL) (NULL) 2 1002 9003 2021-09-01 12:01:01 2021-09-01 12:21:01 60 3 1002 9002 2021-09-02 12:01:01 2021-09-02 12:31:01 70 4 1002 9001 2021-09-05 19:01:01 2021-09-05 19:40:01 81 5 1002 9002 2021-07-06 12:01:01 (NULL) (NULL) 6 1003 9003 2021-09-07 10:01:01 2021-09-07 10:31:01 86 7 1003 9003 2021-09-08 12:01:01 2021-09-08 12:11:01 40 8 1003 9001 2021-09-08 13:01:01 (NULL) (NULL) 9 1003 9002 2021-09-08 14:01:01 (NULL) (NULL) 10 1003 9003 2021-09-08 15:01:01 (NULL) (NULL) 11 1005 9001 2021-09-01 12:01:01 2021-09-01 12:31:01 88 12 1005 9002 2021-09-01 12:01:01 2021-09-01 12:31:01 88 13 1005 9002 2021-09-02 12:11:01 2021-09-02 12:31:01 89 试卷信息表examination_info（exam_id：试卷ID, tag：试卷类别, difficulty：试卷难度, duration：考试时长, release_time：发布时间），示例数据如下： id exam_id tag difficulty duration release_time 1 9001 SQL hard 60 2020-01-01 10:00:00 2 9002 C++ easy 60 2020-02-01 10:00:00 3 9003 算法 medium 80 2020-08-02 10:00:00 请从表中统计出 “当月均完成试卷数”不小于3的用户们爱作答的类别及作答次数，按次数降序输出，示例输出如下： tag tag_cnt C++ 4 SQL 2 算法 1 解释：用户1002和1005在2021年09月的完成试卷数目均为3，其他用户均小于3；然后用户1002和1005作答过的试卷tag分布结果按作答次数降序排序依次为C++、SQL、算法。
示例1

输入

drop table if exists examination_info,exam_record;
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;

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, 'C++', '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', null, null),
(1002, 9003, '2021-09-01 12:01:01', '2021-09-01 12:21:01', 60),
(1002, 9002, '2021-09-02 12:01:01', '2021-09-02 12:31:01', 70),
(1002, 9001, '2021-09-05 19:01:01', '2021-09-05 19:40:01', 81),
(1002, 9002, '2021-07-06 12:01:01', null, null),
(1003, 9003, '2021-09-07 10:01:01', '2021-09-07 10:31:01', 86),
(1003, 9003, '2021-09-08 12:01:01', '2021-09-08 12:11:01', 40),
(1003, 9001, '2021-09-08 13:01:01', null, null),
(1003, 9002, '2021-09-08 14:01:01', null, null),
(1003, 9003, '2021-09-08 15:01:01', null, null),
(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),
(1005, 9002, '2021-09-02 12:11:01', '2021-09-02 12:31:01', 89);

输出

C++|4
SQL|2
算法|1
加载中...