• MySQL查询练习


    表关系

    查询练习

    1、自行创建测试数据;
    2、查询学生总人数;
    3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名;
    4、查询每个年级的班级数,取出班级数最多的前三个年级;
    5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩;
    6、查询每个年级的学生人数;
    7、查询每位学生的学号,姓名,选课数,平均成绩;
    8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数;
    9、查询姓“李”的老师的个数和所带班级数;
    10、查询班级数小于5的年级id和年级名;
    11、查询班级信息,包括班级id、班级名称、年级、年级级别(12为低年级,34为中年级,56为高年级),示例结果如下;
        班级id   班级名称   年级 年级级别
        1  一年一班   一年级    低
    12、查询学过“张三”老师2门课以上的同学的学号、姓名;
    13、查询教授课程超过2门的老师的id和姓名;
    14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名;
    15、查询没有带过高年级的老师id和姓名;
    16、查询学过“张三”老师所教的所有课的同学的学号、姓名;
    17、查询带过超过2个班级的老师的id和姓名;
    18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名;
    19、查询所带班级数最多的老师id和姓名;
    20、查询有课程成绩小于60分的同学的学号、姓名;
    21、查询没有学全所有课的同学的学号、姓名;
    22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名;
    23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名;
    24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名;
    25、删除学习“张三”老师课的score表记录;
    26、向score表中插入一些记录,这些记录要求符合以下条件:①没有上过编号“2”课程的同学学号;②插入“2”号课程的平均成绩;
    27、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分;
    28、查询各科成绩最高和最低的分:以如下形式显示:课程ID,最高分,最低分;
    29、按各科平均成绩从低到高和及格率的百分数从高到低顺序;
    30、课程平均分从高到低显示(显示任课老师);
    31、查询各科成绩前三名的记录(不考虑成绩并列情况)
    32、查询每门课程被选修的学生数;
    33、查询选修了2门以上课程的全部学生的学号和姓名;
    34、查询男生、女生的人数,按倒序排列;
    35、查询姓“张”的学生名单;
    36、查询同名同姓学生名单,并统计同名人数;
    37、查询每门课程的平均成绩,结果按平均成绩升序排列,平均成绩相同时,按课程号降序排列;
    38、查询课程名称为“数学”,且分数低于60的学生姓名和分数;
    39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名;
    40、求选修了课程的学生人数
    41、查询选修“王五”老师所授课程的学生中,成绩最高和最低的学生姓名及其成绩;
    42、查询各个课程及相应的选修人数;
    43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩;
    44、查询每门课程成绩最好的前两名学生id和姓名;
    45、检索至少选修两门课程的学生学号;
    46、查询没有学生选修的课程的课程号和课程名;
    47、查询没带过任何班级的老师id和姓名;
    48、查询有两门以上课程超过80分的学生id及其平均成绩;
    49、检索“3”课程分数小于60,按分数降序排列的同学学号;
    50、删除编号为“2”的同学的“1”课程的成绩;
    51、查询同时选修了物理课和生物课的学生id和姓名;
    查询练习题

    建立相关表

    create table class_grade(
        gid int primary key auto_increment,
        gname varchar(16) not null unique
    );
    
    create table class(
        cid int primary key auto_increment,
        caption varchar(16) not null,
        grade_id int not null,
        foreign key(grade_id) references class_grade(gid)
    );
    
    create table student(
        sid int primary key auto_increment,
        sname varchar(16) not null,
        gender enum('女','男') not null default '女',
        class_id int not null,
        foreign key(class_id) references class(cid)
    );
    
    create table teacher(
        tid int primary key auto_increment,
        tname varchar(16) not null
    );
    
    create table course(
        cid int primary key auto_increment,
        cname varchar(16) not null,
        teacher_id int not null,
        foreign key(teacher_id) references teacher(tid)
    );
    
    create table score(
        sid int not null unique auto_increment,
        student_id int not null,
        course_id int not null,
        score int not null,
        primary key(student_id,course_id),
        foreign key(student_id) references student(sid)
        on delete cascade
        on update cascade,
        foreign key(course_id) references course(cid)
        on delete cascade
        on update cascade
    );
    
    create table teach2cls(
        tcid int not null unique auto_increment,
        tid int not null,
        cid int not null,
        primary key(tid,cid),
        foreign key(tid) references teacher(tid)
        on delete cascade
        on update cascade,
        foreign key(cid) references class(cid)
        on delete cascade
        on update cascade
    );
    
    建表
    建表

    添加测试数据

    # 5 个年级
    insert into class_grade(gname) values
    ('一年级'),
    ('二年级'),
    ('三年级'),
    ('四年级'),
    ('五年级');
    
    
    # 5 个老师
    insert into teacher(tname) values
    ('张三'),
    ('李四'),
    ('王五'),
    ('李杰'),
    ('赵六');
    
    # 12 个班级
    insert into class(caption,grade_id) values
    ('一年一班',1),
    ('一年二班',1),
    ('一年三班',1),
    ('一年四班',1),
    ('一年五班',1),
    ('二年一班',2),
    ('二年二班',2),
    ('三年一班',3),
    ('三年二班',3),
    ('四年一班',4),
    ('四年二班',4),
    ('五年一班',5);
    
    # 10 个课程
    insert into course(cname,teacher_id) values
    ('生物',1),
    ('体育',1),
    ('物理',2),
    ('化学',3),
    ('美术',4),
    ('音乐',2),
    ('语文',3),
    ('数学',4),
    ('地理',2),
    ('研究',1);
    
    # 18 个学生
    insert into student(sname,gender,class_id) values  # 12个学生
    ('孙尚香','',1),
    ('貂蝉','',1),
    ('刘备','',2),
    ('孙二娘','',2),
    ('张飞','',3),
    ('关羽','',4),
    ('林黛玉','',5),
    ('薛宝钗','',6),
    ('宋江','',6),
    ('白骨精','',7),
    ('猪八戒','',8),
    ('王熙凤','',1),
    ('李师师','',2),
    ('金翠莲','',9),
    ('如花','',1),
    ('沙僧','',2),
    ('李美丽','',3),
    ('金角大王','',4);
    
    
    insert into score(student_id,course_id,score) values
    (1,1,60),
    (1,2,59),
    (1,3,58),
    (1,4,22),
    (1,5,59),
    (1,6,60),
    (1,7,99),
    (1,8,100),
    (1,9,88),
    (2,1,99),
    (2,2,99),
    (2,3,89),
    (2,4,60),
    (2,5,59),
    (2,6,33),
    (2,7,56),
    (2,8,59),
    (2,9,60),
    (3,1,59),
    (3,3,30),
    (3,5,28),
    (3,7,70),
    (3,9,60),
    (4,2,59),
    (4,4,100),
    (4,6,90),
    (4,8,80),
    (4,10,88),
    (5,1,59),
    (5,2,33),
    (5,3,12),
    (5,4,88),
    (6,1,60),
    (6,3,99),
    (6,5,100),
    (6,6,60),
    (6,7,59),
    (6,8,100),
    (6,9,88),
    (7,9,20),
    (7,1,36),
    (7,3,57),
    (7,5,60),
    (7,8,60),
    (7,10,60),
    (8,2,61),
    (8,4,59),
    (8,6,62),
    (9,8,59),
    (9,1,60),
    (9,2,61),
    (9,3,21),
    (10,1,70),
    (10,3,88),
    (10,5,68),
    (10,9,99),
    (11,1,89),
    (11,7,99),
    (12,3,100),
    (12,8,60);
    
    
    insert into teach2cls(tid,cid) values
    (1,1),
    (1,2),
    (1,3),
    (1,5),
    (2,4),
    (2,6),
    (2,8),
    (2,9),
    (2,1),
    (2,5),
    (3,7),
    (3,1),
    (3,3),
    (3,5),
    (3,9),
    (4,7),
    (4,2),
    (4,4),
    (4,6),
    (4,8),
    (4,1),
    (1,12),
    (2,12);
    添加测试数据

    参考SQL

    1、自行创建测试数据;
    详见"db5_结构+数据.sql"
    2、查询学生总人数;
    select count(sid) from student ;
    3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名;
    select
      sid,
      sname
    from
      student
    where
      sid in(
        select
          score.student_id
        from
          score
        inner join course on score.course_id=course.cid
        where
          course.cname in(
            '生物',
            '物理'
            )
            and score.score >= 60
            group by
                score.student_id
            having
                count(course_id)=2
          );
    
    
    4、查询每个年级的班级数,取出班级数最多的前三个年级;
    
    select
        gname
    from
        class_grade
    where
        gid in (
            select
                grade_id
            from
                class
            group by
                grade_id
            having
                count(cid) in (
                    select
                        t1.count_cid
                    from
                        (
                            select distinct
                                count(cid) as count_cid
                            from
                                class
                            group by
                                grade_id
                            order by
                                count_cid desc
                            limit 3
                        ) as t1
                    )
                );
    
    
    5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩;
    
    select
        student.sid,
        student.sname,
        t1.avg_score
    from
        student
    inner join (
        select
            student_id,
            avg(score) as avg_score
        from
            score
        group by
            student_id
        having
            avg(score) in (
                (
                    select
                        avg(score) as max_avg_score
                    from
                        score
                    group by
                        student_id
                    order by
                        avg(score) desc
                    limit 1
                ),
                (
                    select
                        avg(score) as min_avg_score
                    from
                        score
                    group by
                        student_id
                    order by
                        avg(score) asc
                    limit 1
                )
            )
    ) as t1 on student.sid = t1.student_id;
    
    6、查询每个年级的学生人数;
    select
        t1.grade_id,
        count(t1.sid) as count_student
    from
        (
            select
                student.sid,
                class.grade_id
            from
                student
            inner join class on student.class_id=class.cid
        ) as t1
    group by
        t1.grade_id;
    
    7、查询每位学生的学号,姓名,选课数,平均成绩;
    select
        student.sid,
        student.sname,
        t1.count_course,
        t1.avg_score
    from
        student
    left join (
        select
            student_id,
            count(course_id) as count_course,
            avg(score) as avg_score
        from
            score
        group by
            student_id
    ) as t1 on student.sid = t1.student_id;
    
    
    8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数;
    
    select
        student.sname,
        course.cname,
        t1.score
    from(
    
            select
                student_id,
                course_id,
                score
            from
                score
            where
                student_id=2
                and score in(
                    (
    
                        select
                            min(score)
                        from
                            score
                        where
                            student_id=2
                    ),
                    (
                        select
                            max(score)
                        from
                            score
                        where
                            student_id=2
                    )
                )
        ) as t1
        inner join student on t1.student_id=student.sid
        inner join course on t1.course_id=course.cid;
    
    9、查询姓“李”的老师的个数和所带班级数;
    
    select
        teacher.tid,
        teacher.tname,
        t1.count_cid
    from
        teacher
    left join (
        select
            tid,
            count(cid) as count_cid
        from
            teach2cls
        where
            tid in (
                select
                    tid
                from
                    teacher
                where
                    tname like '李%'
            )
        group by
            tid
    ) as t1 on teacher.tid = t1.tid
    where
        teacher.tname like '李%';
    
    
    10、查询班级数小于5的年级id和年级名;
    select
        gid,
        gname
    from
        class_grade
    where
        gid in (
            select
                grade_id
            from
                class
            group by
                grade_id
            having
                count(caption)<5
        );
    
    
    11、查询班级信息,包括班级id、班级名称、年级、年级级别(12为低年级,34为中年级,56为高年级),示例结果如下;
        班级id   班级名称   年级 年级级别
        1  一年一班   一年级    低
    # case when ... then
    
    select
        class.cid 班级id,
        class.caption 班级名称,
        class_grade.gname 年级,
        case when class_grade.gid between 1 and 2  then ''
        when class_grade.gid between 3 and 4  then ''
        when class_grade.gid between 5 and 6  then '' else 0 end as '年级级别'
    from
        class,
        class_grade
    where
        class.grade_id = class_grade.gid;
    
    
    12、查询学过“张三”老师2门课以上的同学的学号、姓名;
    
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                student_id
            from
                score
            where
                course_id in (
                    select
                        course.cid
                    from
                        teacher,
                        course
                    where
                        teacher.tid = course.teacher_id
                        and teacher.tname = '张三'
                )
            group by
                student_id
            having
                count(course_id) > 2
        );
    
    13、查询教授课程超过2门的老师的id和姓名;
    
    select
        tid,
        tname
    from
        teacher
    where
        tid in (
            select
                teacher_id
            from
                course
            group by
                teacher_id
            having
                count(cid) > 2
        );
    
    14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名;
    
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select distinct
                student_id
            from
                score
            where
                course_id in (
                    1,
                    2
                )
        );
    
    15、查询没有带过高年级的老师id和姓名;
    
    select
        tid,
        tname
    from
        teacher
    where
        tid not in (
            select
                tid
            from
                teach2cls
            where
                cid in (
                    select
                        cid
                    from
                        class
                    where
                        grade_id in (
                            5,
                            6
                        )
                )
        );
    
    16、查询学过“张三”老师所教的所有课的同学的学号、姓名;
    
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                student_id
            from
                score
            inner join course on score.course_id=course.cid
            where teacher_id in(
                select
                    sid
                from
                    teacher
                where
                    sname='张三'
    
            )
    
    
        )
    
    17、查询带过超过2个班级的老师的id和姓名;
    
    select
        tid,
        tname
    from
        teacher
    where
        tid in (
            select
                teacher_id
            from
                course
            group by
                teacher_id
            having
                count(cid) > 2
        );
    
    18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名;
    
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                t1.student_id
            from
                (
                    select
                        student_id,
                        score
                    from
                        score
                    where
                        course_id = 2
                    group by
                        student_id
                ) as t1,
                (
                    select
                        student_id,
                        score
                    from
                        score
                    where
                        course_id = 1
                    group by
                        student_id
                ) as t2
            where
                t1.student_id = t2.student_id
                and t1.score < t2.score
        );
    
    19、查询所带班级数最多的老师id和姓名;
    
    # 考虑班级数并列最多的情况
    
    select
        tid,
        tname
    from
        teacher
    where
        tid in (
            select
                tid
            from
                teach2cls
            group by
                tid
            having
                count(cid) = (
                    select
                        count(cid)
                    from
                        teach2cls
                    group by
                        tid
                    order by
                        count(cid) desc
                    limit 1
                )
        );
    
    20、查询有课程成绩小于60分的同学的学号、姓名;
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select distinct
                student_id
            from
                score
            where
                score < 60
        );
    
    21、查询没有学全所有课的同学的学号、姓名;
    select
        sid,
        sname
    from
        student
    where
        sid not in (
            select
                student_id
            from
                score
            group by
                student_id
            having
                count(course_id) = (
                    select
                        count(cid)
                    from
                        course
                )
        );
    22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名;
    
    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
                )
            group by
                student_id
        );
    
    23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名;
    
    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
                )
            group by
                student_id
        )
        and sid != 1;
    
    24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名;
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                score.student_id
            from
                score,
                (
                    select
                        course_id
                    from
                        score
                    where
                        student_id = 2
                ) as t1
            where
                score.course_id = t1.course_id
                and score.student_id != 2
            group by
                score.student_id
            having
                count(score.course_id) = (
                    select
                        count(course_id)
                    from
                        score
                    where
                        student_id = 2
                )
        );
    
    
    25、删除学习“张三”老师课的score表记录;
    delete from
        score
    where
        course_id in (
            select
                course.cid
            from
                course,
                teacher
            where
                course.teacher_id = teacher.tid
                and teacher.tname = '张三'
        );
    
    26、向score表中插入一些记录,这些记录要求符合以下条件:①没有上过编号“2”课程的同学学号;②插入“2”号课程的平均成绩;
    
    # 实际结果会和上面一题有冲突,张三老师所教的2号课程
    
    insert into score(student_id,course_id,score)
    select
        t1.sid,
        2,
        t2.avg_score
    from
        (
            select
                sid
            from
                student
            where
                sid not in (
                    select
                        student_id
                    from
                        score
                    where
                        course_id = 2
                )
        ) as t1,
        (
            select
                avg(score) as avg_score
            from
                score
            where
                course_id = 2
        ) as t2;
    
    27、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分;
    
    # 有效成绩含所有课程,包括语数英
    
    select
        t1.student_id as 学生ID,
        (select score.score from score left join course on score.course_id = course.cid where course.cname = '语文' and score.student_id = t1.student_id) as 语文,
        (select score.score from score left join course on score.course_id = course.cid where course.cname = '数学' and score.student_id = t1.student_id) as 数学,
        (select score.score from score left join course on score.course_id = course.cid where course.cname = '音乐' and score.student_id = t1.student_id) as 英语,
        count(t1.course_id) as 有效课程数,
        avg(t1.score) as 有效平均分
    from
        score as t1
    group by
        t1.student_id
    order by
        avg(t1.score) asc;
    
    28、查询各科成绩最高和最低的分:以如下形式显示:课程ID,最高分,最低分;
    
    select
        course.cid as 课程ID,
        max(score.score) as 最高分,
        min(score.score) as 最低分
    from
        course
    left join score on course.cid = score.course_id
    group by
        score.course_id;
    
    29、按各科平均成绩从低到高和及格率的百分数从高到低顺序;
    
    select
        course_id,
        avg(score) as avg_score,
        sum(case when score.score > 60 then 1 else 0 end) / count(1) * 100 as 及格率
    from
        score
    group by
        course_id
    order by
        avg(score) desc,
        及格率 asc;
    
    30、课程平均分从高到低显示(显示任课老师);
    select
        course.cname,
        t1.avg_score,
        teacher.tname
    from
        course,
        teacher,
        (
            select
                course_id,
                avg(score) as avg_score
            from
                score
            group by
                course_id
            order by
                avg_score desc
        ) as t1
    where
        course.cid = t1.course_id
        and course.teacher_id = teacher.tid
    order by
        t1.avg_score desc;
    
    31、查询各科成绩前三名的记录(不考虑成绩并列情况)
    select
        score.sid,
        score.student_id,
        score.course_id,
        score.sid,
        t1.first_score,
        t1.second_score,
        t1.third_score
    from
        score
    inner join (
        select
            s1.sid,
            (select score from score as s2 where s1.course_id = s2.course_id order by score desc limit 0,1) as first_score,
            (select score from score as s3 where s1.course_id = s3.course_id order by score desc limit 1,1) as second_score,
            (select score from score as s4 where s1.course_id = s4.course_id order by score desc limit 2,1) as third_score
        from
            score as s1
    ) as t1 on score.sid = t1.sid
    where
        score.score in (
            t1.first_score,
            t1.second_score,
            t1.third_score
        );
    
    32、查询每门课程被选修的学生数;
    
    # 包含了没有被选修的课程显示0
    select
        course.cid,
        ifnull(t1.count_students,0) as count_student
    from
        course
    left join (
        select
            course_id,
            count(student_id) as count_students
        from
            score
        group by
            course_id
    ) as t1 on course.cid = t1.course_id;
    
    33、查询选修了2门以上课程的全部学生的学号和姓名;
    
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                student_id
            from
                score
            group by
                student_id
            having
                count(course_id) > 2
        );
    
    34、查询男生、女生的人数,按倒序排列;
    
    select
        gender,
        count(sid) as count_student
    from
        student
    group by
        gender
    order by
        count_student desc;
    
    35、查询姓“张”的学生名单;
    
    select
        student.sid,
        student.sname,
        student.gender,
        class.caption
    from
        student
    inner join class on student.class_id = class.cid
    where
        student.sname like '张%';
    
    36、查询同名同姓学生名单,并统计同名人数;
    select
        sname,
        count(sname) as count_sname
    from
        student
    group by
        sname
    having
        count(sname) > 1;
    
    37、查询每门课程的平均成绩,结果按平均成绩升序排列,平均成绩相同时,按课程号降序排列;
    
    select
        course_id,
        avg(score) as avg_score
    from
        score
    group by
        course_id
    order by
        avg_score,
        course_id desc;
    
    38、查询课程名称为“数学”,且分数低于60的学生姓名和分数;
    select
        student.sname,
        t1.score
    from
        student
    inner join (
        select
            score.student_id,
            score.score
        from
            score
        inner join course on score.course_id = course.cid
        where
            course.cname = '数学'
            and score.score < 60
    ) as t1 on student.sid = t1.student_id;
    39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名;
    select
        sid,
        sname
    from
        student
    where sid in (
        select
            student_id
        from
            score
        where
            course_id = 3
            and score > 80
    );
    40、求选修了课程的学生人数
    select
        course_id,
        count(student_id) as count_student
    from
        score
    group by
        course_id;
    
    41、查询选修“王五”老师所授课程的学生中,成绩最高和最低的学生姓名及其成绩;
    # 教的课可能包含多门,按课程id来分的!包含了最高,最低成绩相等的情况
    
    select
        student.sname,
        t2.course_id,
        t2.score,
        t2.max_score,
        t2.min_score
    from
        student
    inner join (
        select
            score.student_id,
            score.course_id,
            score.score,
            t1.max_score,
            t1.min_score
        from
            score,
            (
                select
                    course_id,
                    max(score) as max_score ,
                    min(score) as min_score
                from
                    score
                where
                    course_id in (
                        select
                            cid
                        from
                            course
                        inner join teacher on course.teacher_id = teacher.tid
                        where
                            teacher.tname = '王五'
                    )
                group by
                    course_id
            ) as t1
        where
            score.course_id = t1.course_id
            and score.score in (
                max_score,
                min_score
            )
    ) as t2 on student.sid = t2.student_id;
    
    42、查询各个课程及相应的选修人数;
    # 包含了没有被选修的课程显示0
    
    select
        course.cname,
        ifnull(t1.count_student,0) as count_student
    from
        course
    left join (
        select
            course_id,
            count(student_id) as count_student
        from
            score
        group by
            course_id
    ) as t1 on course.cid = t1.course_id;
    43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩;
    # 不同的学生之间,成绩相同 这里有问题!!
    select distinct
        s1.student_id,
        s2.student_id,
        s1.course_id as s1_course_id,
        s2.course_id as s2_course_id,
        s1.score,
        s2.score
    from
        score as s1,
        score as s2
    where
        s1.course_id != s2.course_id
        and s1.score = s2.score;
    
    select distinct             # 同一个学生,成绩相同
        s1.student_id,
        s2.student_id,
        s1.course_id as s1_course_id,
        s2.course_id as s2_course_id,
        s1.score,
        s2.score
    from
        score as s1,
        score as s2
    where
        s1.student_id = s2.student_id
        and s1.course_id != s2.course_id
        and s1.score = s2.score;
    44、查询每门课程成绩最好的前两名学生id和姓名;
    
    # 这个有排名 包括了成绩相同的!
    select
        c.sname,
        d.cname,
        a.score
    from
        score a
    inner join (
        select course_id, score, rank
            from (
                 select a.course_id, a.score, count(*) as rank
                    from (select course_id, score
                           from score
                            group by course_id, score
                            order by course_id, score desc) a
                    inner join (select course_id, score
                                from score
                                group by course_id, score
                                order by course_id, score desc) b
                    on a.course_id = b.course_id
                        and a.score <= b.score
                 group by course_id, score
            ) t1
            where rank in (1, 2)
            order by course_id, rank
       ) b
    on a.course_id = b.course_id
        and a.score = b.score
    inner join student c
        on a.student_id = c.sid
    inner join course d
        on a.course_id = d.cid;
    
    45、检索至少选修两门课程的学生学号;
    select
        student_id
    from
        score
    group by
        student_id
    having
        count(course_id) >= 2;
    46、查询没有学生选修的课程的课程号和课程名;
    
    select
        cid,
        cname
    from
        course
    where
        cid not in (
            select
                course_id
            from
                score
            group by
                course_id
        );
    
    47、查询没带过任何班级的老师id和姓名;
    select
        tid,
        tname
    from
        teacher
    where
        tid not in (
            select
                tid
            from
                teach2cls
            group by
                tid
        );
    
    48、查询有两门以上课程超过80分的学生id及其平均成绩;
    select
        student_id,
        avg(score) as avg_score
    from
        score
    where
        student_id in (
            select
                student_id
            from
                score
            where
                score > 80
            group by
                student_id
            having
                count(course_id) > 2
        )
    group by
        student_id;
    
    49、检索“3”课程分数小于60,按分数降序排列的同学学号;
    select
        student_id,
        score
    from
        score
    where
        course_id = 3
        and score < 60
    order by
        score desc;
    
    50、删除编号为“2”的同学的“1”课程的成绩;
    delete from
        score
    where
        sid = (
            select
                t1.sid
            from
                (
                    select
                        sid
                    from
                        score
                    where
                        student_id = 2
                        and course_id = 1
                ) as t1
        );
    
    51、查询同时选修了物理课和生物课的学生id和姓名;
    select
        sid,
        sname
    from
        student
    where
        sid in (
            select
                student_id
            from
                score
            where
                course_id in (
                    select
                        cid
                    from
                        course
                    where
                        course.cname in (
                            '物理',
                            '生物'
                        )
                )
            group by
                student_id
            having
                count(course_id) = 2
        );
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  • 原文地址:https://www.cnblogs.com/runnermark/p/9258140.html
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