mysql-50题

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数据表介绍

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--1.学生表
Student(SId,Sname,Sage,Ssex)
--SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
--2.课程表
Course(CId,Cname,TId)
--CId 课程编号,Cname 课程名称,TId 教师编号
--3.教师表
Teacher(TId,Tname)
--TId 教师编号,Tname 教师姓名
--4.成绩表
SC(SId,CId,score)
--SId 学生编号,CId 课程编号,score 分数

练习题目

1.查询” 01 “课程比” 02 “课程成绩高的学生的信息及课程分数

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-- 此处可以先考虑分别查询 01和02课程的学员id和分数
select SId,score from SC where CId = '01';
select SId,score from SC where CId = '02';
-- 对比结果可以清楚的知道,两个表中有些SId不对应,不对应就没有可比性
-- 因此可以对两个结果做join,条件就是SId要相等,
-- 并且01的成绩要比02大
select s1.SId,s1.score
from 
(select SId,score from SC where CId = '01') s1
join
(select SId,score from SC where CId = '02') s2
on s1.SId = s2.SId
where s1.score > s2.score

-- 通过以上的sql得到了符合条件的学员id和分数,再到学员表中获取学员信息
select stu.SId,stu.Sname,s.score 
from student as stu 
right join (
        select s1.SId,s1.score
        from 
        (select SId,score from SC where CId = '01') s1
        join
        (select SId,score from SC where CId = '02') s2
        on s1.SId = s2.SId
        where s1.score > s2.score
    ) as s
on stu.SId = s.SId;
  1. 查询同时存在” 01 “课程和” 02 “课程的情况
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-- 本题和上一题内容相似,我们只需要把01和02的学员的SID作为连接条件就可以
select s1.*
from 
(select SId,score from SC where CId = '01') s1
join
(select SId,score from SC where CId = '02') s2
on s1.SId = s2.SId
  1. 查询存在” 01 “课程但可能不存在” 02 “课程的情况(不存在时显示为 null )
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select s1.SId,s2.score
from 
(select SId,score from SC where CId = '01') s1
left join
(select SId,score from SC where CId = '02') s2
on s1.SId = s2.SId
  1. 查询不存在” 01 “课程但存在” 02 “课程的情况
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select * from SC 
where SId not in(select SId from SC where CId = '01')
and CId = '02'

5.查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

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-- 此题主要考核 分组后的条件过滤
select SC.SId,Sname,round(avg(score),2) as avg_score
from SC,Student
where SC.SId = Student.SId
group by SC.SId,Sname having avg_score >= 60;

6.查询在 SC 表存在成绩的学生信息

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-- 此题主要考核 数据去重 distinct 
select distinct stu.* from Student stu join SC on SC.SId = stu.SId;

7.查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

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select stu.SId,stu.Sname,count(SC.CId) as total ,sum(SC.score) as sum_score
from Student as stu left join SC on stu.SId = SC.SId
group by stu.SId,stu.Sname;

8.查询「李」姓老师的数量

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select count(*) from teacher where Tname like '李%';

9.查询学过「张三」老师授课的同学的信息

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select stu.*
from Student as stu 
join SC on stu.SId = SC.SId
join course as C on SC.CId = C.CId
join Teacher as T on C.TId = T.TId
where T.Tname = '张三';

10.查询没有学全所有课程的同学的信息

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-- 排除法,找到所有学过全部课程的学生,
select * from Student where SId not in(
    select SId from SC group by SId having count(CId) = (select count(*) from course)
)

11.查询至少有一门课与学号为” 01 “的同学所学相同的同学的信息

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select distinct stu.* 
from student as stu 
left join sc on sc.SId = stu.SId 
where sc.CId in (select CId from sc where SId = '01');

12.查询和” 01 “号的同学学习的课程 完全相同的其他同学的信息

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-- 注意要对比的是课程ID号,在对比课程数
select s2.SId
from SC as s1 join SC as s2
on s1.CId = s2.CId and s1.SId = '01' and s2.SId != '01'  
group by s2.SId 
having count(s1.SId) = (select count(*) from SC where SId = '01');

select stu.* 
from student as stu 
left join sc on sc.SId = stu.SId 
join ( select CId from sc where SId = '01') as t on t.CId = sc.CId 
group by stu.SId having count(sc.SId) = 5;

13.查询没学过”张三”老师讲授的任一门课程的学生姓名

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select SId,Sname from Student where SId not in 
(select SId from SC
    where CId = (
        select Course.Cid from Course 
        join Teacher on Teacher.TId = Course.TId 
        where Teacher.Tname = '张三'
        ))

14.查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

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select SC.SId,Student.Sname,round(avg(SC.score),2) as avg_sc 
from SC join Student on Student.SId = SC.SId
where SC.score < 60 group by SC.SId,Student.Sname 
having count(SC.CId) >=2;

15.检索” 01 “课程分数小于 60，按分数降序排列的学生信息

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select SC.SId,Student.Sname,SC.score
from SC join Student  on SC.SId = Student.SId 
where SC.CId = '01' and SC.score < 60 
order by SC.score desc;

16.按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

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select SC.*,s2.avg_sc from SC 
join  (select SId, avg(score) as avg_sc from SC group by SId) as s2
on SC.SId = s2.SId
order by avg_sc desc, SC.SId;


--最佳解决方案 王宇鹏
select a.sname,b.score 语文,c.score 数学,d.score 英语,avg(e.score) 
from student a 
left join sc b on a.sid=b.sid and b.cid='01' 
left join sc c on a.sid=c.sid and c.cid='02' 
left join sc d on a.sid=d.sid and d.cid='03' 
left join sc e on a.sid=e.sid 
group by a.sname,语文,数学,英语
order by avg(e.score) desc;

17.查询各科成绩最高分、最低分和平均分：
以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率 及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

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select SC.CId,C.Cname,
max(SC.score) as '最高分',
min(SC.score) as '最低分',
avg(SC.score) as '平均分',
count(SC.CId) as '选修人数',
SUM(CASE WHEN SC.score >= 60 THEN 1 ELSE 0 END) / count(SC.CId) as '及格率',
SUM(CASE WHEN SC.score >= 70 and SC.score < 80 THEN 1 ELSE 0 END) / count(SC.CId) as '中等率',
SUM(CASE WHEN SC.score >= 80 and SC.score < 90 THEN 1 ELSE 0 END) / count(SC.CId) as '优良率',
SUM(CASE WHEN SC.score >= 90 THEN 1 ELSE 0 END) / count(SC.CId) as '优秀率'
from SC,Course as C
where SC.CId = C.CId
group by SC.CId,C.Cname
order by '选修人数' desc,SC.CId;

18.按各科平均成绩进行排序，并显示排名， Score 重复时保留名次空缺

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select s2.CId,s2.avg_sc,count(distinct s1.avg_sc) as Rank
from
(select  avg(score) as avg_sc from SC group by CId) as s1
join 
(select CId,avg(score) as avg_sc from SC group by CId) as s2
on s1.avg_sc >= s2.avg_sc
group by s2.CId order by Rank;

-- 解析过程
select s1.*,s2.*
from
(select  CId,avg(score) as avg_sc from SC group by CId) as s1
join 
(select CId,avg(score) as avg_sc from SC group by CId) as s2
on s1.avg_sc >= s2.avg_sc
group by s2.CId order by Rank;
-- 在这种情况下 去统计s1.平均分 还是去统计s2.平均分 的次数,数据中都有重复
-- 如果能把s1中的出现重复的平均分数去重,再去按照s1.平均分去统计次数就正常
    +------+----------+------+----------+
    | CId  | avg_sc   | CId  | avg_sc   |
    +------+----------+------+----------+
    | 01   | 64.50000 | 01   | 64.50000 |
    | 02   | 79.33333 | 01   | 64.50000 |
    | 03   | 70.00000 | 01   | 64.50000 |
    | 04   | 79.30000 | 01   | 64.50000 |
  --| 5    | 70.00000 | 01   | 64.50000 |
    | 02   | 79.33333 | 02   | 79.33333 |
    | 02   | 79.33333 | 03   | 70.00000 |
    | 03   | 70.00000 | 03   | 70.00000 |
    | 04   | 79.30000 | 03   | 70.00000 |
  --| 5    | 70.00000 | 03   | 70.00000 |
    | 02   | 79.33333 | 04   | 79.30000 |
    | 04   | 79.30000 | 04   | 79.30000 |
    | 02   | 79.33333 | 5    | 70.00000 |
    | 03   | 70.00000 | 5    | 70.00000 |
    | 04   | 79.30000 | 5    | 70.00000 |
  --| 5    | 70.00000 | 5    | 70.00000 |
    +------+----------+------+----------+

19.按各科平均成绩进行排序，并显示排名， Score 重复时不保留名次空缺

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select b.CId,b.avg_sc,@i := @i+1 as Rank 
from (select @i := 0) a,
(select CId,round(avg(Score),2) as avg_sc from SC group by CId order by avg_sc desc) b;

20.查询学生的总成绩，并进行排名，总分重复时保留名次空缺

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select s2.SId,s2.avg_sc,count(distinct s1.avg_sc) as Rank
from
(select  sum(score) as avg_sc from SC group by SId) as s1
join 
(select SId,sum(score) as avg_sc from SC group by SId) as s2
on s1.avg_sc >= s2.avg_sc
group by s2.SId order by Rank;

21.查询学生的总成绩，并进行排名，总分重复时不保留名次空缺

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select b.SId,b.avg_sc,@i := @i+1 as Rank 
from (select @i := 0) a,
(select SId,sum(Score) as avg_sc from SC group by sId order by avg_sc desc) b;

22.统计各科成绩各分数段人数：课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0]及所占百分比

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select Course.CId,Course.Cname,
sum(CASE WHEN SC.score >= 85 and SC.score <= 100 THEN 1 ELSE 0 END) '[100-85]',
concat(round(sum(CASE WHEN SC.score >= 85 and SC.score <= 100 THEN 1 ELSE 0 END)/count(SC.SId),2)*100,'%') as '百分比',
sum(CASE WHEN SC.score >= 70 and SC.score < 85 THEN 1 ELSE 0 END) '[85-70]',
concat(round(sum(CASE WHEN SC.score >= 70 and SC.score < 85 THEN 1 ELSE 0 END)/count(SC.SId),2)*100,'%') as '百分比',
sum(CASE WHEN SC.score >= 60 and SC.score < 70 THEN 1 ELSE 0 END) '[70-60]',
concat(round(sum(CASE WHEN SC.score >= 60 and SC.score < 70 THEN 1 ELSE 0 END)/count(SC.SId),2)*100,'%') as '百分比',
sum(CASE WHEN SC.score >= 0 and SC.score < 60 THEN 1 ELSE 0 END) '[60-0]',
concat(round(sum(CASE WHEN SC.score >= 0 and SC.score < 60 THEN 1 ELSE 0 END)/count(SC.SId),2)*100,'%') as '百分比'
from SC,Course
where SC.CId = Course.CId
group by Course.CId,Course.Cname;

23.查询各科成绩前三名的记录

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(select CId,score from SC where CId = '01' order by score desc limit 3) 
union all
(select CId,score from SC where CId = '02' order by score desc limit 3) 
union all
(select CId,score from SC where CId = '03' order by score desc limit 3)

24.查询每门课程被选修的学生数

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select CId,count(SId) from SC group by CId;

25.查询出只选修两门课程的学生学号和姓名

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select SC.SId,Student.Sname
from SC join Student on SC.SId = Student.SId
group by SC.SId,Student.Sname having count(SC.CId) = 2;

26.查询男生、女生人数

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select Ssex,count(*) from Student group by Ssex;

27.查询名字中含有「风」字的学生信息

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select * from Student where Sname like '%风%';

28.查询同名同性学生名单，并统计同名人数

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select s1.Sname,count(s1.Sname)
from Student s1 join Student s2 
on s1.Sname = s2.Sname and s1.Ssex = s2.Ssex and s1.SId != s2.SId
group by s1.Sname;

29.查询 1990 年出生的学生名单

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select * from Student where year(Sage) = 1990;

30.查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

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select CId,avg(score) as avg_sc 
from SC group by CId order by avg_sc desc,CId;

31.查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩

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select SC.SId,Stu.Sname,round(avg(SC.score),2) as avg_sc 
from SC join Student as Stu on SC.SId = Stu.SId
group by SC.SId,Stu.Sname having avg_sc >= 85;

32.查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

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select C.Cname,Stu.Sname,SC.score
from Course as C join SC  on C.CId = SC.CId 
join Student as Stu on SC.SId = Stu.SId
where C.Cname = '数学' and SC.score < 60;

33.查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）

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select Student.Sname,Course.Cname,SC.score
from Student left join SC on Student.SId = SC.SId
left join Course on SC.CId = Course.CId
order by Student.Sname;

-- 张波
select a.SId,a.sname,b.score 语文,c.score 数学,d.score 英语 
from student a 
left join sc b on a.sid=b.sid and b.cid='01' 
left join sc c on a.sid=c.sid and c.cid='02' 
left join sc d on a.sid=d.sid and d.cid='03' 
group by a.SId,a.sname,语文,数学,英语
order by a.Sid;

34.查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数

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select Student.Sname,Course.Cname,SC.score
from Student,Course,SC 
where Student.SId = SC.SId and SC.CId = Course.CId
and SC.score > 70;

35.查询不及格的课程

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select Student.Sname,Course.Cname,SC.score
from Student,Course,SC 
where Student.SId = SC.SId and SC.CId = Course.CId
and SC.score < 60;

36.查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名

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select SC.SId,Student.Sname
from SC join Student on SC.SId = Student.SId
where SC.Score > 80 and SC.CId = '01';

37.求每门课程的学生人数

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select CId,count(SId) from SC group by CId;

38.成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

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select Student.SId,Student.Sname,SC.score
from Student join SC on Student.SId = SC.SId
join Course on SC.CId = Course.CId
join Teacher on Teacher.TId = Course.TId
where Teacher.Tname = '张三';
order by SC.score desc limit 1;

39.成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

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-- 查询张三老师授课的学生中最高分数,查询所有等于最高分的

-- -- 先查询最高分数
-- select max(SC.score) 
-- from SC join Course on SC.CId = Course.CId
-- join Teacher on Teacher.TId = Course.TId
-- where Teacher.Tname = '张三'

-- 追加 分数条件
select Student.SId,Student.Sname,SC.score
from Student join SC on Student.SId = SC.SId
join Course on SC.CId = Course.CId
join Teacher on Teacher.TId = Course.TId
where Teacher.Tname = '张三' 
and SC.score = (select max(SC.score) 
from SC join Course on SC.CId = Course.CId
join Teacher on Teacher.TId = Course.TId
where Teacher.Tname = '张三');

-- 王宇鹏
select a.sname,b.score 
from student a join sc b on a.sid=b.sid 
and b.cid in (select cid from course where tid in (select tid from teacher where tname='张三')) 
join (select cid,max(score) m from sc group by cid) c on b.cid=c.cid and b.score=c.m;


-- 张波
select stu.*,
max(SC.score) as 成绩
from Student as stu 
join SC on stu.SId = SC.SId
join course as C on SC.CId = C.CId
join Teacher as T on C.TId = T.TId
where T.Tname = '张三';

40.查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

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select  s1.CId,s1.SId,s1.Score
from SC s1 join SC s2
on s1.CId != s2.CId and s1.score = s2.score and s1.SId = s2.SId
order by s1.Score;

select distinct s1.SId,s1.CId,s1.Score
from SC s1 join SC s2 
on s1.CId != s2.CId and s1.score = s2.score
group by  s1.SId,s1.CId,s1.Score

SELECT DISTINCT s1.sid,s1.cid,s1.score 
FROM sc s1,sc s2 WHERE s1.cid != s2.cid AND s1.score = s2.score

41.查询每门课程成绩最好的前两名

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(select CId,score from SC where CId = '01' order by score desc limit 2) 
union all
(select CId,score from SC where CId = '02' order by score desc limit 2) 
union all
(select CId,score from SC where CId = '03' order by score desc limit 2)

42.统计每门课程的学生选修人数（超过 5 人的课程才统计）。

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select CId,count(SId) from SC group by CId having count(SId) > 5;

43.检索至少选修两门课程的学生学号

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select SId,count(CId) as num from SC group by SId having num >=2;

44.查询选修了全部课程的学生信息

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select SId from SC group by SId 
having count(CId) = (select count(*) from Course);

45.查询各学生的年龄，只按年份来算

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select Stu.SId,Stu.Sname,(year(now()) - year(Stu.Sage)) as '年龄' 
from Student as stu;

46.按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

TIMESTAMPDIFF() 从日期时间表达式中减去间隔
https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html

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select student.SId,student.Sname,
TIMESTAMPDIFF(YEAR,student.Sage,CURDATE()) from student

47.查询本周过生日的学生

返回日期从范围内的数字日历星期1到53

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select *from student 
where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(CURDATE());

48.查询下周过生日的学生

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select *
from student 
where WEEKOFYEAR(student.Sage)=WEEKOFYEAR(CURDATE())+1;

49.查询本月过生日的学生

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select *
from student 
where MONTH(student.Sage)=MONTH(CURDATE());

50.查询下月过生日的学生

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select *
from student 
where MONTH(student.Sage)=MONTH(CURDATE())+1;

数据Data

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--学生表 Student
create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-12-20' , '男');
insert into Student values('04' , '李云' , '1990-12-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-01-01' , '女');
insert into Student values('07' , '郑竹' , '1989-01-01' , '女');
insert into Student values('09' , '张三' , '2017-12-20' , '女');
insert into Student values('10' , '李四' , '2017-12-25' , '女');
insert into Student values('11' , '李四' , '2012-06-06' , '女');
insert into Student values('12' , '赵六' , '2013-06-13' , '女');
insert into Student values('13' , '孙七' , '2014-06-01' , '女');

-- 科目表 Course
create table Course(CId varchar(10),Cname nvarchar(10),TId varchar(10));
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

-- 教师表 Teacher
create table Teacher(TId varchar(10),Tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

-- 成绩表 SC
create table SC(SId varchar(10),CId varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);