数据库---多表查询练习

多表查询练习

导出现有数据库数据：

• mysqldump -u用户名 -p密码 数据库名称 > 导出文件路径 # 结构+数据
• mysqldump -u用户名 -p密码 -d 数据库名称 > 导出文件路径 # 结构

导入现有数据库数据：

• mysql -uroot -p密码 数据库名称 < 文件路径

1.准备数据：init.sql文件内容：

/*
     数据导入：
     Navicat Premium Data Transfer

     Source Server         : localhost
     Source Server Type    : MySQL
     Source Server Version : 50624
     Source Host           : localhost
     Source Database       : sqlexam

     Target Server Type    : MySQL
     Target Server Version : 50624
     File Encoding         : utf-8

     Date: 10/21/2016 06:46:46 AM
    */

    SET NAMES utf8;
    SET FOREIGN_KEY_CHECKS = 0;

    -- ----------------------------
    --  Table structure for `class`
    -- ----------------------------
    DROP TABLE IF EXISTS `class`;
    CREATE TABLE `class` (
      `cid` int(11) NOT NULL AUTO_INCREMENT,
      `caption` varchar(32) NOT NULL,
      PRIMARY KEY (`cid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

    -- ----------------------------
    --  Records of `class`
    -- ----------------------------
    BEGIN;
    INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
    COMMIT;

    -- ----------------------------
    --  Table structure for `course`
    -- ----------------------------
    DROP TABLE IF EXISTS `course`;
    CREATE TABLE `course` (
      `cid` int(11) NOT NULL AUTO_INCREMENT,
      `cname` varchar(32) NOT NULL,
      `teacher_id` int(11) NOT NULL,
      PRIMARY KEY (`cid`),
      KEY `fk_course_teacher` (`teacher_id`),
      CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

    -- ----------------------------
    --  Records of `course`
    -- ----------------------------
    BEGIN;
    INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
    COMMIT;

    -- ----------------------------
    --  Table structure for `score`
    -- ----------------------------
    DROP TABLE IF EXISTS `score`;
    CREATE TABLE `score` (
      `sid` int(11) NOT NULL AUTO_INCREMENT,
      `student_id` int(11) NOT NULL,
      `course_id` int(11) NOT NULL,
      `num` int(11) NOT NULL,
      PRIMARY KEY (`sid`),
      KEY `fk_score_student` (`student_id`),
      KEY `fk_score_course` (`course_id`),
      CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
      CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;

    -- ----------------------------
    --  Records of `score`
    -- ----------------------------
    BEGIN;
    INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
    COMMIT;

    -- ----------------------------
    --  Table structure for `student`
    -- ----------------------------
    DROP TABLE IF EXISTS `student`;
    CREATE TABLE `student` (
      `sid` int(11) NOT NULL AUTO_INCREMENT,
      `gender` char(1) NOT NULL,
      `class_id` int(11) NOT NULL,
      `sname` varchar(32) NOT NULL,
      PRIMARY KEY (`sid`),
      KEY `fk_class` (`class_id`),
      CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

    -- ----------------------------
    --  Records of `student`
    -- ----------------------------
    BEGIN;
    INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');
    COMMIT;

    -- ----------------------------
    --  Table structure for `teacher`
    -- ----------------------------
    DROP TABLE IF EXISTS `teacher`;
    CREATE TABLE `teacher` (
      `tid` int(11) NOT NULL AUTO_INCREMENT,
      `tname` varchar(32) NOT NULL,
      PRIMARY KEY (`tid`)
    ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

    -- ----------------------------
    --  Records of `teacher`
    -- ----------------------------
    BEGIN;
    INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');
    COMMIT;

    SET FOREIGN_KEY_CHECKS = 1;

准备数据

2.从init.sql文件中导入数据

• #准备表、记录
• mysql> create database db1;
• mysql> use db1;
• mysql> source /root/init.sql

3.题目

1、查询所有的课程的名称以及对应的任课老师姓名
2、查询学生表中男女生各有多少人
3、查询物理成绩等于100的学生的姓名
4、查询平均成绩大于八十分的同学的姓名和平均成绩
5、查询所有学生的学号，姓名，选课数，总成绩
6、查询姓李老师的个数
7、查询没有报李平老师课的学生姓名
8、查询物理课程比生物课程高的学生的学号
9、查询没有同时选修物理课程和体育课程的学生姓名
10、查询挂科超过两门(包括两门)的学生姓名和班级
11、查询选修了所有课程的学生姓名
12、查询李平老师教的课程的所有成绩记录
13、查询全部学生都选修了的课程号和课程名
14、查询每门课程被选修的次数
15、查询之选修了一门课程的学生姓名和学号
16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
17、查询平均成绩大于85的学生姓名和平均成绩
18、查询生物成绩不及格的学生姓名和对应生物分数
19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
20、查询每门课程成绩最好的前两名学生姓名
21、查询不同课程但成绩相同的学号，课程号，成绩
22、查询没学过“叶平”老师课程的学生姓名以及选修的课程名称；
23、查询所有选修了学号为1的同学选修过的一门或者多门课程的同学学号和姓名；
24、任课最多的老师中学生单科成绩最高的学生姓名

4.答案

#1、查询所有的课程的名称以及对应的任课老师姓名
        select
            course.cname,
            teacher.tname
        from
            course
        inner join teacher on course.teacher_id = teacher.tid;

    #2、查询学生表中男女生各有多少人
        select
            gender,
            count(1)   # count(sid)
        from
            student
        group by
            gender;

    #3、查询物理成绩等于100的学生的姓名
        select
            sname
        from
            student
        where
            sid in(
                select
                    t1.student_id
                from
                    score t1
                inner join(
                    select
                        cid
                    from
                        course
                    where
                        cname = '物理'
                ) t2 on t1.course_id = t2.cid
                where
                    t1.num = 100
            );

    #4、查询平均成绩大于八十分的同学的姓名和平均成绩
        select
            t1.sname,
            t2.avg_num
        from
            student as t1
        inner join(
            select
                student_id,
                avg(num) as avg_num
            from
                score
            group by
                student_id
            having
                avg(num) > 80
        ) as t2 on t1.sid = t2.student_id;

    #5、查询所有学生的学号，姓名，选课数，总成绩(注意：对于那些没有选修任何课程的学生也算在内)
        select
            t1.sid,
            t1.sname,
            t2.count_course,
            t2.sum_num
        from
            student as t1
        left join(
            select
                student_id,
                count(course_id) as count_course,
                sum(num) as sum_num
            from
                score
            group by
                student_id
        ) as t2 on t1.sid = t2.student_id;

    #6、 查询姓李老师的个数
        select
            count(tid)
        from
            teacher
        where
            tname like '李%';

    #7、 查询没有报李平老师课的学生姓名
        select
            sname
        from
            student
        where
            sid not in(
                select distinct
                    student_id
                from
                    score
                where
                    course_id in (
                        select
                            cid
                        from
                            course
                        inner join teacher on course.teacher_id = teacher.tid
                        where teacher.tname = '李平老师'
                    )
            );

    #8、 查询物理课程比生物课程高的学生的学号(分别得到物理成绩表与生物成绩表，然后连表即可)
        select
            t1.student_id,
            t1.num,
            t2.num
        from
            (
                select
                    student_id,
                    num
                from
                    score
                where
                    course_id = (
                        select
                            cid
                        from
                            course
                        where
                            cname = '物理'
                    )
            ) as t1
        inner join (
            select
                student_id,
                num
            from
                score
            where
                course_id = (
                    select
                        cid
                    from
                        course
                    where
                        cname = '生物'
                )
        ) as t2 on t1.student_id = t2.student_id
        where
            t1.num > t2.num;

    #9、 查询没有同时选修物理课程和体育课程的学生姓名
    # 包含了物理，体育都没选得
    select
        sname
    from
        student
    where
        sid not in (
            select
                t1.student_id
            from
                (
                    select
                        student_id,
                        course_id
                    from
                        score
                    where
                        course_id in (
                            select
                                cid
                            from
                                course
                            where
                                cname in (
                                    '物理',
                                    '体育'
                                )
                        )
                ) as t1
            group by
                t1.student_id
            having
                count(t1.student_id) = 2
        );
        # 只选修了一门
        select
            sname
        from
            student
        where
            sid in (
                select
                    t1.student_id
                from
                    (
                        select
                            student_id,
                            course_id
                        from
                            score
                        where
                            course_id in (
                                select
                                    cid
                                from
                                    course
                                where
                                    cname in (
                                        '物理',
                                        '体育'
                                    )
                            )
                    ) as t1
                group by
                    t1.student_id
                having
                    count(t1.student_id) = 1
            );
            # 另一种方法：
            SELECT
                student.sname
            FROM
                student
            WHERE
                sid IN (
                    SELECT
                        student_id
                    FROM
                        score
                    WHERE
                        course_id IN (
                            SELECT
                                cid
                            FROM
                                course
                            WHERE
                                cname = '物理'
                            OR cname = '体育'
                        )
                    GROUP BY
                        student_id
                    HAVING
                        COUNT(course_id) = 1
                );

    #10、查询挂科超过两门(包括两门)的学生姓名和班级
        select
            t1.caption,
            t2.sname
        from
            class as t1
        inner join (
            select
                sname,
                class_id
            from
                student
            where
                sid in (
                    select
                        student_id
                    from
                        score
                    where
                        num < 60
                    group by
                        student_id
                    having
                        count(sid) >= 2
                )
        ) as t2 on t1.cid = t2.class_id;
        #另一种方法：
        SELECT
            student.sname,
            class.caption
        FROM
            student
        INNER JOIN (
            SELECT
                student_id
            FROM
                score
            WHERE
                num < 60
            GROUP BY
                student_id
            HAVING
                count(course_id) >= 2
        ) AS t1
        INNER JOIN class ON student.sid = t1.student_id
        AND student.class_id = class.cid;

    #11、查询选修了所有课程的学生姓名
        select
            sname
        from
            student
        where
            sid in (
                select
                    student_id
                from
                    score
                group by
                    student_id
                having
                    count(sid) = (
                        select
                            count(cid)
                        from
                            course
                    )
            );

    #12、查询李平老师教的课程的所有成绩记录
        select
            *
        from
            score
        where
            course_id in (
                select
                    cid
                from
                    course
                inner join teacher on course.teacher_id = teacher.tid
                where
                    teacher.tname = '李平老师'
            );

    #13、查询全部学生都选修了的课程号和课程名(取所有学生数，然后基于score表的课程分组，找出count(student_id)等于学生数即可)
        select
            cid,
            cname
        from
            course
        where
            cid in (
                select
                    course_id
                from
                    score
                group by
                    course_id
                having
                    count(sid) = (select count(sid) from student)
            );

    #14、查询每门课程被选修的次数
        select
            course_id,
            count(sid)
        from
            score
        right join course on score.course_id = course.cid
        group by
            course_id
        order by
            course_id;

        SELECT
            course_id,
            COUNT(student_id)
        FROM
            score
        GROUP BY
            course_id;

    #15、查询之选修了一门课程的学生姓名和学号
        select
            sid,
            sname
        from
            student
        where
            sid in (
                select
                    student_id
                from
                    score
                group by
                    student_id
                having
                    count(sid) = 1
            );

    #16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
        select distinct
            num
        from
            score
        order by
            num desc;

    #17、查询平均成绩大于85的学生姓名和平均成绩
        select
            student.sname,
            t1.avg_num
        from
            student
        inner join (
            select
                student_id,
                avg(num) as avg_num
            from
                score
            group by
                student_id
            having
                avg(num) > 85
        ) as t1 on student.sid = t1.student_id;

    #18、查询生物成绩不及格的学生姓名和对应生物分数
        select
            sname,
            t1.num
        from
            student
        inner join (
            select
                student_id,
                num
            from
                score
            inner join course on score.course_id = course.cid
            where course.cname = '生物'
                and score.num < 60
        ) as t1 on student.sid = t1.student_id;
        # 另一种方法：
        select
            student.sname,
            score.num
        from
            score
        left join course on score.course_id = course.cid
        left join student on score.student_id = student.sid
        where
            course.cname = '生物'
            and score.num < 60;

    #19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
        select
            sname,
            t1.avg_num
        from
            student
        inner join (
            select
                student_id,
                avg(num) as avg_num
            from
                score
            where
                course_id in (
                    select
                        cid
                    from
                        course
                    inner join teacher on course.teacher_id = teacher.tid
                    where teacher.tname = '李平老师'
                )
            group by
                student_id
            order by
                avg_num desc
            limit 1
        ) as t1 on student.sid = t1.student_id;

    #20、查询每门课程成绩最好的前两名学生姓名
        select
            student.sname,
            num_table.course_id,
            num_table.first_num,
            num_table.second_num
        from
            student
        inner join (
            select
                score.sid,
                score.course_id as course_id,
                score.student_id,
                t.first_num as first_num,
                t.second_num as second_num
            from
                score
            left join
                (
                    select
                        sid,
                        (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,
                        (select num from score as s3 where s3.course_id = s1.course_id order by num desc limit 1,1) as second_num
                    from
                        score as s1
                ) as t on score.sid = t.sid
            where score.num <= t.first_num and score.num >= t.second_num
        ) as num_table on student.sid = num_table.student_id;

    #21、查询不同课程但成绩相同的学号，课程号，成绩
        select distinct
            s1.student_id,
            s1.course_id,
            s1.num,
            s2.num
        from
            score as s1,
            score as s2
        where
            s1.num = s2.num
            and s1.course_id != s2.course_id;

        select distinct
            *
        from
            score as s1,
            score as s2
        where
            s1.num = s2.num

    #22、查询没学过李平老师课程的学生姓名以及选修的课程名称；
        select
            student.sname,
            course.cname
        from
            (
                select
                    student_id,
                    course_id
                from
                    score
                where
                    course_id not in (
                        select
                            cid
                        from
                            course
                        inner join teacher on course.teacher_id = teacher.tid
                        where teacher.tname = '李平老师'
                    )
            ) as t1
        inner join course on t1.course_id = course.cid
        inner join student on t1.student_id = student.sid
        order by student.sname;

    #23、查询所有选修了学号为1的同学选修过的一门或者多门课程的同学学号和姓名；
         select
            student_id,
            sname,
            count(course_id)
        from
            score
        left join student on score.student_id = student.sid
        where
            student_id != 1
            and course_id in
                (
                    select
                        course_id
                    from
                        score
                    where
                        student_id = 1
                )
        group by student_id
        # 另一种方法：
        select
            sid,
            sname
        from
            student
        where
            sid in (
                select
                    student_id
                from
                    score
                where
                    course_id in (
                        select
                            course_id
                        from
                            score
                        where
                            student_id = 1
                    )
            )
            and sid !=1

    #24、任课最多的老师中学生单科成绩最高的学生姓名
        select
            sid,
            sname
        from
            student
        where
            sid in (
                select distinct
                    t1.id_students
                from
                    (
                        select
                            group_concat(student_id) as id_students,
                            course_id,
                            max(num)
                        from
                            score
                        where
                            course_id in (
                                select
                                    cid
                                from
                                    course
                                where
                                    teacher_id in (
                                        select
                                            teacher_id
                                        from
                                            course
                                        group by
                                            teacher_id
                                        having
                                            count(cid) = (
                                                select
                                                    count(cid)
                                                from
                                                    course
                                                group by
                                                    teacher_id
                                                order by
                                                    count(cid) desc
                                                limit 1
                                            )
                                    )
                            )
                        group by
                            course_id
                    ) as t1
            );