mysql基础学习

二、操作表

1、自行创建测试数据；

-- 创建数据库
create database practice charset utf8;
-- 1、自行创建测试数据；
--
-- 创建班级表:class
create table class(
cid int primary key auto_increment,
caption char(10),
grade_id int not null
);
-- 插入数据到班级表：
insert into class(caption,grade_id) values ('一年一班',1),('二年一班',2),('三年二班',3);
-- 创建学生表：student
create table student(
sid int primary key auto_increment,
sname char(10) not null,
gender enum("男","女") default "男",
class_id int not null,
foreign key(class_id) references class(cid)
on delete cascade
on update cascade);
--插入数据到student表
insert into student(sname,gender,class_id) values ('乔丹','女',1),('艾弗森','女',1),('科比','男',2);
--创建老师表：teacher
create table teacher(
tid int primary key auto_increment,
tname char(10) not null
);
-- 插入数据到teacher表
insert into teacher(tname) values ('张三'),('李四'),('王五');

-- 创建课程表：course
create table course(
cid int primary key auto_increment,
cname char(10) not null,
teacher_id int,
foreign key(teacher_id) references teacher(tid)
on delete cascade on update cascade
);
-- 插入数据到课程表：
insert into course(cname,teacher_id) values ('生物',1),('体育',1),('物理',2);
--
-- 创建成绩表：score
create table score(
sid int primary key auto_increment,
student_id int not null,
course_id int not null,
score int default 0,
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
);
--插入数据到score
insert into score(student_id,course_id,score) values (1,1,60),(1,2,59),(2,2,99);
--
-- 创建年级表：class_grade
create table class_grade(
gid int primary key auto_increment,
gname char(10) not null
);
-- 插入数据到class_grade
insert into class_grade(gname) values ('一年级'),('二年级'),('三年级');
--
-- 创建班级任职表
create table teach2cls(
tcid int primary key auto_increment,
tid int not null,
cid int not null,
foreign key(tid) references teacher(tid) on delete cascade on update cascade,
foreign key(cid) references course(cid) on delete cascade on update cascade
);
-- 插入数据到teach2cls
insert into teach2cls(tid,cid) values (1,1),(1,2),(2,1),(3,2);

--更多测试数据
insert class_grade(gname) values ('四年级'),('五年级');
insert class(caption,grade_id) values ('四年一班',4),('四年二班',4),('五年一班',5),('五年二班',5);
insert teacher (tname) values ('甜甜'),('小花'),('阿狗'),("阿猫");
insert course(cname,teacher_id) values('语文',4),('数学',5),('英语',6),('化学',3),('美术',4);
insert teach2cls (tid,cid) values(4,6),(5,5),(6,4),(6,2);

insert student(sname,gender,class_id) values
('alsa','女',4),('lily','女',5),('jack','男',6),('alsa','女',7),
('lucy','女',1),('bob','男',3),('乔丹','女',4),('nico','女',5),
('alex','男',3),('张良','男',4),('lily','女',2),('jack','男',7),
('kitty','女',5),('诸葛','男',5),('妲己','女',4),('甄姬','女',6);

insert score (student_id, course_id,score) values
(4,1,58),(5,2,88),(6,3,73),(16,4,75),(16,5,92),
(7,4,65),(8,5,98),(9,6,72),(16,6,88),(17,7,63),(18,7,77),(19,7,90),
(11,3,81),(10,5,85),(12,1,63),(12,2,87),
(13,6,55),(14,3,55),(15,5,41),(6,1,80);

-- 2、查询学生总人数；
select count(sid) from student;
-- +------------+
-- | count(sid) |
-- +------------+
-- |         19 |
-- +------------+
--
-- 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 student_id from
  score  inner join course  on score.course_id = course.cid
  where cname='生物' or cname='物理' and score>=60
  group by student_id
);
-- +-----+--------+
-- | sid | sname  |
-- +-----+--------+
-- |   1 | 乔丹   |
-- |   4 | alsa   |
-- |  12 | alex   |
-- |   6 | jack   |
-- |  11 | nico   |
-- +-----+--------+
--
-- 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
  t1.gname,t2.class_count
from
  class_grade t1
inner join
  (select
    grade_id,count(cid) as class_count
  from
    class
  group by
    grade_id) as t2
on
  t1.gid=t2.grade_id
order by
  t2.class_count desc
limit 3;
-- +-----------+-------------+
-- | gname     | class_count |
-- +-----------+-------------+
-- | 四年级    |           2 |
-- | 五年级    |           2 |
-- | 一年级    |           1 |
-- +-----------+-------------+
--
-- 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
  t1.sid,
  t1.sname,
  t2.avg_score
from
  student as t1
inner join(
  select
    student_id,avg(score) as avg_score
  from
    score
  group by
    student_id
  having
    avg(score) in(
      (select avg(score) as lowest_score from score group by student_id order by avg(score) asc limit 1),
      (select avg(score) as highest_score from score group by student_id order by avg(score) desc limit 1)
    )
) as t2
on t1.sid=t2.student_id;
-- +-----+-----------+-----------+
-- | sid | sname     | avg_score |
-- +-----+-----------+-----------+
-- |   2 | 艾弗森    |   99.0000 |
-- |  15 | jack      |   41.0000 |
-- +-----+-----------+-----------+
--
-- 6、查询每个年级的学生人数；
select
  gname,
  student_count
from
  class_grade as t1
inner join
  (select
    grade_id,count(sid) as student_count
  from
    student
  inner join
    class
  on student.class_id = class.cid
  group by
    grade_id) as t2
on t1.gid=t2.grade_id;
-- +-----------+---------------+
-- | gname     | student_count |
-- +-----------+---------------+
-- | 一年级    |             3 |
-- | 二年级    |             2 |
-- | 三年级    |             2 |
-- | 四年级    |             8 |
-- | 五年级    |             4 |
-- +-----------+---------------+
--
-- 7、查询每位学生的学号，姓名，选课数，平均成绩；
select
  t1.sid,t1.sname,count_course,avg_score
from
  student as t1
inner join
  (select
    student_id,count(course_id) as count_course,avg(score) as avg_score
  from score
  group by
    student_id) as t2
on t1.sid=t2.student_id;
-- +-----+-----------+--------------+-----------+
-- | sid | sname     | count_course | avg_score |
-- +-----+-----------+--------------+-----------+
-- |   1 | 乔丹      |            2 |   59.5000 |
-- |   2 | 艾弗森    |            1 |   99.0000 |
-- |   5 | lily      |            1 |   88.0000 |
-- |   6 | jack      |            2 |   76.5000 |
-- |   8 | lucy      |            1 |   98.0000 |
-- |   9 | bob       |            1 |   72.0000 |
-- |  12 | alex      |            2 |   75.0000 |
-- |  13 | 张良      |            1 |   55.0000 |
-- |  18 | 妲己      |            1 |   77.0000 |
-- +-----+-----------+--------------+-----------+

-- 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
 t3.sid,
 t3.sname,
 t4.cname,
 t3.score
from
 course as t4
inner join
 (select
  sid,
  sname,
  course_id,
  score
 from
  student as t1
 inner join
  (select
   student_id,
   course_id,
   score
  from
   score
  where
   student_id=2 and
   score in(
    (select score from score where student_id=2 order by score limit 1),
    (select score from score where student_id=2 order by score desc limit 1)
    )
   )as t2
 on t1.sid=t2.student_id) as t3
on t4.cid=t3.course_id;
-- +-----+-----------+--------+-------+
-- | sid | sname     | cname  | score |
-- +-----+-----------+--------+-------+
-- |   2 | 艾弗森    | 体育   |    99 |
-- |   2 | 艾弗森    | 数学   |    68 |
-- +-----+-----------+--------+-------+
--
-- 9、查询姓“李”的老师的个数和所带班级数；

select
    count_li,
    count(teach2cls.cid)as count_class
from
    teach2cls
inner join(
    select
        tid,
        count(tid)as count_li
    from
        teacher
    where
        tname like "李%"
    )as teach
on
    teach2cls.tid=teach.tid
group by
    teach2cls.tid;
-- +--------------------+-----------------+
-- | 姓李老师个数       | 所带班级数      |
-- +--------------------+-----------------+
-- |                  1 |               1 |
-- +--------------------+-----------------+
--
-- 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(cid)<5);
-- +-----+-----------+
-- | gid | gname     |
-- +-----+-----------+
-- |   1 | 一年级    |
-- |   2 | 二年级    |
-- |   3 | 三年级    |
-- |   4 | 四年级    |
-- |   5 | 五年级    |
-- +-----+-----------+
--
-- 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
select
 class.cid as "班级id",
 class.caption as "班级名称",
 class_grade.gname as "年级",
 case
  when class_grade.gid between 1 and 2 
   then "低"
  when class_grade.gid between 3 and 4 
   then "中"
  when class_grade.gid between 5 and 6 
   then "高"
  else 
   0
 end as "年级级别"
from
 class
inner join
 class_grade
on class.grade_id=class_grade.gid
-- +----------+--------------+-----------+--------------+
-- | 班级id   | 班级名称     | 年级      | 年级级别     |
-- +----------+--------------+-----------+--------------+
-- |        1 | 一年一班     | 一年级    | 低           |
-- |        2 | 二年一班     | 二年级    | 低           |
-- |        3 | 三年二班     | 三年级    | 中           |
-- |        4 | 四年一班     | 四年级    | 中           |
-- |        5 | 四年二班     | 四年级    | 中           |
-- |        6 | 五年一班     | 五年级    | 高           |
-- |        7 | 五年二班     | 五年级    | 高           |
-- +----------+--------------+-----------+--------------+
--
-- 12、查询学过“张三”老师2门课以上的同学的学号、姓名；
select
 t1.sid,
 t1.sname
from
 student as t1
inner join
 (select
  student_id
 from
  score
 inner join
  course
 on score.course_id=course.cid
 where
  course.teacher_id=
  (select
   tid
  from
   teacher
  where
   tname="张三")
 group by
  student_id
 having
  count(course_id)>=2) as t2
on t1.sid=t2.student_id;
-- +-----+--------+
-- | sid | sname  |
-- +-----+--------+
-- |   1 | 乔丹   |
-- |  12 | alex   |
-- +-----+--------+
--
-- 13、查询教授课程超过2门的老师的id和姓名；
select
 teacher.tid,
 teacher.tname
from
 teacher
inner join(
 select
  teacher_id
 from
  course
 group by
  teacher_id
 having
  count(cid)>=2) as t1
on teacher.tid=t1.teacher_id;
-- +-----+--------+
-- | tid | tname  |
-- +-----+--------+
-- |   1 | 张三   |
-- |   4 | 甜甜   |
-- +-----+--------+
--
-- 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
  student_id
 from
  score
 where
  course_id=1 or course_id=2
 group by
  student_id
 having
  count(course_id)=2);
-- +-----+--------+
-- | sid | sname  |
-- +-----+--------+
-- |   1 | 乔丹   |
-- |  12 | alex   |
-- +-----+--------+
--
-- 15、查询没有带过高年级的老师id和姓名；
select
    tid,
    tname
from
    teacher
where
    tid in(
    select
        tid
    from
        teach2cls
    inner join
        class
    on teach2cls.cid=class.cid
    where
        grade_id<5
    group by
         tid);
-- +-----+--------+
-- | tid | tname  |
-- +-----+--------+
-- |   1 | 张三   |
-- |   2 | 李四   |
-- |   3 | 王五   |
-- |   5 | 小花   |
-- |   6 | 阿狗   |
-- +-----+--------+
--
-- 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 distinct 
        student_id
    from
        score
    where
        course_id in (
        select
            cid
        from
            course
        where
            teacher_id in(
            select
                tid
            from
                teacher
            where
                tname='张三'
            )
        )
    );
-- +-----+-----------+
-- | sid | sname     |
-- +-----+-----------+
-- |   1 | 乔丹      |
-- |   2 | 艾弗森    |
-- |   5 | lily      |
-- |   6 | jack      |
-- |  12 | alex      |
-- +-----+-----------+
--
-- 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
        tid
    from
        teach2cls
    group by
        tid
    having
        count(cid)>=2
);
-- +-----+--------+
-- | tid | tname  |
-- +-----+--------+
-- |   1 | 张三   |
-- |   6 | 阿狗   |
-- +-----+--------+
--
-- 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 s1.student_id
  from score as s1 inner join score as s2 on s1.student_id = s2.student_id and s1.course_id = 1 and s2.course_id = 2
  where s1.score < s2.score);
-- +-----+-------+
-- | sid | sname |
-- +-----+-------+
-- |  12 | alex  |
-- +-----+-------+
--
-- 19、查询所带班级数最多的老师id和姓名；
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
            )
    );
-- +-----+--------+
-- | tid | tname  |
-- +-----+--------+
-- |   1 | 张三   |
-- |   6 | 阿狗   |
-- +-----+--------+
--
-- 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
            student_id
        from
            score
        where
            score<60
    );
-- +-----+--------+
-- | sid | sname  |
-- +-----+--------+
-- |   1 | 乔丹   |
-- |  13 | 张良   |
-- +-----+--------+
--
-- 21、查询没有学全所有课的同学的学号、姓名；
select
    sid,
    sname
from
    student
left join (
    select
        student_id
    from
        score
    group by
        student_id
    having
        count(course_id)<(
            select count(cid) from course)
    )as t1
on
    student.sid=t1.student_id
-- +-----+-----------+
-- | sid | sname     |
-- +-----+-----------+
-- |   1 | 乔丹      |
-- |   2 | 艾弗森    |
-- |   5 | lily      |
-- |   6 | jack      |
-- |   8 | lucy      |
-- |   9 | bob       |
-- |  12 | alex      |
-- |  13 | 张良      |
-- |  18 | 妲己      |
-- +-----+-----------+
--
-- 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
            distinct student_id
        from
            score
        where
            course_id in(
                select
                    course_id
                from
                    score
                where
                    student_id =1
            )
    )
    and sid !=1;
-- +-----+-----------+
-- | sid | sname     |
-- +-----+-----------+
-- |  12 | alex      |
-- |   6 | jack      |
-- |   2 | 艾弗森    |
-- |   5 | lily      |
-- +-----+-----------+
--
-- 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
            distinct student_id
        from
            score
        where
            course_id in(
                select
                    course_id
                from
                    score
                where
                    student_id =1
            )
    )
    and sid !=1;
-- +-----+-----------+
-- | sid | sname     |
-- +-----+-----------+
-- |  12 | alex      |
-- |   6 | jack      |
-- |   2 | 艾弗森    |
-- |   5 | lily      |
-- +-----+-----------+
--
-- 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 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 cid from course where teacher_id =(
        select tid from teacher where 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；
insert 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,课程数和平均分；
select
    student_id,
    (select score from score where course_id =(select cid from course where cname='语文') and score.student_id =s1.student_id ) as '语文',
    (select score from score where course_id =(select cid from course where cname='数学') and score.student_id =s1.student_id ) as '数学',
    (select score from score where course_id =(select cid from course where cname='英语') and score.student_id =s1.student_id ) as '英语',
    count(course_id) as '有效课程数',
    avg(score) as '有效平均分'
from
    score as s1
group by
    student_id
order by
    avg(score);
-- +------------+--------+--------+--------+-----------------+-----------------+
-- | student_id | 语文   | 数学   | 英语   | 有效课程数      | 有效平均分      |
-- +------------+--------+--------+--------+-----------------+-----------------+
-- |          1 |   NULL |   NULL |   NULL |               3 |         62.3333 |
-- |         13 |   NULL |   NULL |     55 |               2 |         69.0000 |
-- |         12 |   NULL |   NULL |   NULL |               2 |         75.0000 |
-- |          9 |   NULL |   NULL |     72 |               2 |         77.5000 |
-- |          6 |   NULL |   NULL |   NULL |               3 |         78.6667 |
-- |         18 |   NULL |   NULL |   NULL |               2 |         80.0000 |
-- |          2 |     88 |     68 |   NULL |               3 |         85.0000 |
-- |          5 |   NULL |   NULL |   NULL |               1 |         88.0000 |
-- |          8 |   NULL |     98 |   NULL |               2 |         90.5000 |
-- +------------+--------+--------+--------+-----------------+-----------------+
--
-- 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_id as '课程id',
    max(score.score) as '最高分',
    min(score.score) as '最低分'
from
    course
left join score
on score.course_id=course.cid 
group by course_id;
-- +----------+-----------+-----------+
-- | 课程id   | 最高分    | 最低分    |
-- +----------+-----------+-----------+
-- |     NULL |      NULL |      NULL |
-- |        1 |        80 |        60 |
-- |        2 |        99 |        59 |
-- |        3 |        73 |        68 |
-- |        4 |        88 |        88 |
-- |        5 |        98 |        68 |
-- |        6 |        72 |        55 |
-- |        7 |        77 |        77 |
-- +----------+-----------+-----------+
--
-- 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(sid) * 100 as percent
from
    score
group by
    course_id
order by
    avg(score) asc,percent desc;
-- +-----------+-----------+----------+
-- | course_id | avg_score | percent  |
-- +-----------+-----------+----------+
-- |         6 |   63.5000 |  50.0000 |
-- |         1 |   67.6667 | 100.0000 |
-- |         3 |   70.5000 | 100.0000 |
-- |         7 |   77.0000 | 100.0000 |
-- |         5 |   83.0000 | 100.0000 |
-- |         2 |   83.1111 |  88.8889 |
-- |         4 |   88.0000 | 100.0000 |
-- +-----------+-----------+----------+
--
-- 30、课程平均分从高到低显示（现实任课老师）；
select
    t1.cid,
    t1.tname,
    t2.avg_score
from(
    select
        teacher.tid as tid,
        teacher.tname as tname,
        course.cid as cid
    from
        teacher
    inner join
        course
    on teacher.tid = teacher_id
    )as t1
inner join
    (select course_id,avg(score)as avg_score from score group by course_id )as t2
on
    t1.cid=t2.course_id
order by
    avg_score desc;
-- +-----+--------+-----------+
-- | cid | tname  | avg_score |
-- +-----+--------+-----------+
-- |   4 | 甜甜   |   88.0000 |
-- |   2 | 张三   |   83.1111 |
-- |   5 | 小花   |   83.0000 |
-- |   7 | 王五   |   77.0000 |
-- |   3 | 李四   |   70.5000 |
-- |   1 | 张三   |   67.6667 |
-- |   6 | 阿狗   |   63.5000 |
-- +-----+--------+-----------+
--
-- 31、查询各科成绩前三名的记录(不考虑成绩并列情况) ；
select
  student_id,
  score,
  course_id
from score r1
where (SELECT count(1)
       from (select distinct
               score,
               course_id
             from score) r2
       where r2.course_id = r1.course_id AND r2.score > r1.score) <= 2
order by course_id, score DESC;
-- +------------+-------+-----------+
-- | student_id | score | course_id |
-- +------------+-------+-----------+
-- |          6 |    80 |         1 |
-- |         12 |    63 |         1 |
-- |          1 |    60 |         1 |
-- |          2 |    99 |         2 |
-- |          5 |    88 |         2 |
-- |         12 |    87 |         2 |
-- |          6 |    73 |         3 |
-- |          1 |    68 |         3 |
-- |          2 |    88 |         4 |
-- |          8 |    98 |         5 |
-- |          2 |    68 |         5 |
-- |          9 |    72 |         6 |
-- |         13 |    55 |         6 |
-- |         18 |    77 |         7 |
-- +------------+-------+-----------+
--
-- 32、查询每门课程被选修的学生数；
select
    course_id,
    count(student_id)
from
    score
group by
    course_id;
-- +-----------+-------------------+
-- | course_id | count(student_id) |
-- +-----------+-------------------+
-- |         1 |                 3 |
-- |         2 |                 9 |
-- |         3 |                 2 |
-- |         4 |                 1 |
-- |         5 |                 2 |
-- |         6 |                 2 |
-- |         7 |                 1 |
-- +-----------+-------------------+
--
-- 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);
-- +-----+-----------+
-- | sid | sname     |
-- +-----+-----------+
-- |   1 | 乔丹      |
-- |   2 | 艾弗森    |
-- |   6 | jack      |
-- +-----+-----------+
--
-- 34、查询男生、女生的人数，按倒序排列；
select
    gender,
    count(sid)
from
    student
group by
    gender
order by   
    count(sid) desc;
-- +--------+------------+
-- | gender | count(sid) |
-- +--------+------------+
-- | 女     |          5 |
-- | 男     |          4 |
-- +--------+------------+
--
-- 35、查询姓“张”的学生名单；
select
    *
from
    student
where
    sname like "张%";
-- +-----+--------+--------+----------+
-- | sid | sname  | gender | class_id |
-- +-----+--------+--------+----------+
-- |  13 | 张良   | 男     |        4 |
-- +-----+--------+--------+----------+
--
-- 36、查询同名同姓学生名单，并统计同名人数；
select
    sname,
    count(sid)
from
    student
group by
    sname
having
    count(sid)>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)
from
    score
group by
    course_id
order by
    avg(score),
    course_id desc;
-- +-----------+------------+
-- | course_id | avg(score) |
-- +-----------+------------+
-- |         6 |    63.5000 |
-- |         1 |    67.6667 |
-- |         3 |    70.5000 |
-- |         7 |    77.0000 |
-- |         5 |    83.0000 |
-- |         2 |    83.1111 |
-- |         4 |    88.0000 |
-- +-----------+------------+
--
-- 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
        student_id,
        score
    from
        score
    where score.score<60 and course_id in (
        select
            cid
        from
            course
        where cname='数学'
    )
)as t1
on 
    t1.student_id=student.sid;
--
-- 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
    coalesce(student_id,"总人数")as '课程id',
    count(course_id) as '人数'
from
    score
group by
    student_id
with rollup;
-- +-----------+--------+
-- | 课程id    | 人数   |
-- +-----------+--------+
-- | 1         |      3 |
-- | 2         |      3 |
-- | 5         |      1 |
-- | 6         |      3 |
-- | 8         |      2 |
-- | 9         |      2 |
-- | 12        |      2 |
-- | 13        |      2 |
-- | 18        |      2 |
-- | 总人数    |     20 |
-- +-----------+--------+
--  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；
select
    s1.student_id,
    low_score,
    s2.student_id,
    high_score
from(
    select
        tid,
        student_id,
        score as low_score
    from
        (select student_id,cid,cname,score,tid
        from score
        inner join
            (select tid,tname,cid,cname from teacher inner join course on teacher.tid=course.teacher_id where tname='王五')as t1
        on score.course_id=t1.cid)as t2 order by score limit 1) as s1
    inner join (
        select tid,student_id,score as high_score from
            (select student_id,cid,cname,score,tid
            from score
            inner join
                (select tid,tname,cid,cname from teacher
                inner join
                    course
                on teacher.tid=course.teacher_id where tname='王五')as t1
            on score.course_id=t1.cid)as t2 order by score desc limit 1) as s2
    on s1.tid=s2.tid;
-- +------------+-----------+------------+------------+
-- | student_id | low_score | student_id | high_score |
-- +------------+-----------+------------+------------+
-- |         18 |        77 |         18 |         77 |
-- +------------+-----------+------------+------------+
--
-- 42、查询各个课程及相应的选修人数；
select
    course_id ,
    count(student_id)
from
    score
group by
    course_id;
-- +-----------+-------------------+
-- | course_id | count(student_id) |
-- +-----------+-------------------+
-- |         1 |                 3 |
-- |         2 |                 9 |
-- |         3 |                 2 |
-- |         4 |                 1 |
-- |         5 |                 2 |
-- |         6 |                 2 |
-- |         7 |                 1 |
-- +-----------+-------------------+
--
-- 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；
select distinct
    s1.course_id,
    s1.student_id,
    s1.score,
    s2.course_id,
    s2.student_id,
    s2.score
from
    score as s1,
    score as s2
where
    s1.score = s2.score and s1.course_id != s2.course_id;
-- +-----------+------------+-------+-----------+------------+-------+
-- | course_id | student_id | score | course_id | student_id | score |
-- +-----------+------------+-------+-----------+------------+-------+
-- |         4 |          2 |    88 |         2 |          5 |    88 |
-- |         5 |          2 |    68 |         3 |          1 |    68 |
-- |         2 |          5 |    88 |         4 |          2 |    88 |
-- |         3 |          1 |    68 |         5 |          2 |    68 |
-- +-----------+------------+-------+-----------+------------+-------+
--
-- 44、查询每门课程成绩最好的前两名学生id和姓名；
select student.sid,student.sname,course.cname, score.score
    from score
inner join (
    select course_id, score, ranking
        from (
             select a.course_id, a.score, count(1) as ranking
                from
                    (select course_id, score from score group by course_id, score order by course_id, score desc)as a
                inner join
                    (select course_id, score from score group by course_id, score order by course_id, score desc)as b
                on a.course_id = b.course_id and a.score <= b.score group by course_id, score
        ) as t1
        where ranking in (1, 2) order by course_id, ranking)as s1
on score.course_id = s1.course_id and score.score = s1.score
inner join student
    on score.student_id = student.sid
inner join course
    on score.course_id = course.cid;
-- +-----+-----------+--------+-------+
-- | sid | sname     | cname  | score |
-- +-----+-----------+--------+-------+
-- |  12 | alex      | 生物   |    63 |
-- |   6 | jack      | 生物   |    80 |
-- |   2 | 艾弗森    | 体育   |    99 |
-- |   5 | lily      | 体育   |    88 |
-- |   6 | jack      | 物理   |    73 |
-- |   1 | 乔丹      | 物理   |    68 |
-- |   2 | 艾弗森    | 语文   |    88 |
-- |   8 | lucy      | 数学   |    98 |
-- |   2 | 艾弗森    | 数学   |    68 |
-- |   9 | bob       | 英语   |    72 |
-- |  13 | 张良      | 英语   |    55 |
-- |  18 | 妲己      | 化学   |    77 |
-- +-----+-----------+--------+-------+
--
-- 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;
-- +------------+
-- | student_id |
-- +------------+
-- |          1 |
-- |          2 |
-- |          6 |
-- |          8 |
-- |          9 |
-- |         12 |
-- |         13 |
-- |         18 |
-- +------------+
--
-- 46、查询没有学生选修的课程的课程号和课程名；
select
    course.cid,
    course.cname
from
    course
left join
    score
on
    course.cid=score.course_id
where
    score.student_id is null;
-- +-----+--------+
-- | cid | cname  |
-- +-----+--------+
-- |   8 | 美术   |
-- +-----+--------+
--
-- 47、查询没带过任何班级的老师id和姓名；
select
    teacher.tid,
    tname
from
    teacher
left join
    teach2cls
on
    teacher.tid=teach2cls.tid
where
    teach2cls.tcid is null;
-- +-----+--------+
-- | tid | tname  |
-- +-----+--------+
-- |   7 | 阿猫   |
-- +-----+--------+
--
-- 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)
from
    score
where
    score>80
group by
    student_id
having
    count(course_id)>2;
--
-- 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
    score<60 and course_id=3
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 student_id='2' and course_id='1';
--
-- 51、查询同时选修了物理课和生物课的学生id和姓名；
select
    student.sid,
    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 = '生物'
            )
        group by
            student_id
        having
            count(course_id) = 2
    );
-- +-----+--------+
-- | sid | sname  |
-- +-----+--------+
-- |   1 | 乔丹   |
-- |   6 | jack   |
-- +-----+--------+