MySql:学生表、教师表、课程表、分数表 练习_教师学生课程三个表的设计

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前言

面试经常被问，记录练习方便查看，原文不是mysql，有些许差别，已经逐条验证改为mysql,标题带！的有问题，之后会再修改的
转载自：参考文章

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一、创建表并初始化数据

进入mysql环境：

//进入mysql环境
mysql -u root -p
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创建自己的数据库wjj：

create database wjj;
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进入自己的数据库wjj：

use wjj;
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创建表：

表说明： student(学生表)、teacher(教师表)、course(课程表)、sc(分数表)

//学生表
create table student(  
   sno varchar(10) primary key,  
   sname varchar(20),  
   sage int(2),  
   ssex varchar(5)  
); 
 //教师表
create table teacher(  
   tno varchar(10) primary key,  
   tname varchar(20)  
); 
 //课程表
create table course(  
   cno varchar(10),  
   cname varchar(20),  
   tno varchar(20),  
   constraint pk_course primary key (cno,tno)  
); 
 //分数表
create table sc(  
   sno varchar(10),  
   cno varchar(10),  
   score int(11),  
   constraint pk_sc primary key (sno,cno)  
);
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插入初始化数据:

/*******初始化学生表的数据******/  
insert into student values ('s001','张三',23,'男');  
insert into student values ('s002','李四',23,'男');  
insert into student values ('s003','吴鹏',25,'男');  
insert into student values ('s004','琴沁',20,'女');  
insert into student values ('s005','王丽',20,'女');  
insert into student values ('s006','李波',21,'男');  
insert into student values ('s007','刘玉',21,'男');  
insert into student values ('s008','萧蓉',21,'女');  
insert into student values ('s009','陈萧晓',23,'女');  
insert into student values ('s010','陈美',22,'女'); 
/******************初始化教师表***********************/  
insert into teacher values ('t001', '刘阳');  
insert into teacher values ('t002', '谌燕');  
insert into teacher values ('t003', '胡明星');  
/***************初始化课程表****************************/  
insert into course values ('c001','J2SE','t002');  
insert into course values ('c002','Java Web','t002');  
insert into course values ('c003','SSH','t001');  
insert into course values ('c004','Oracle','t001');  
insert into course values ('c005','SQL SERVER 2005','t003');  
insert into course values ('c006','C#','t003');  
insert into course values ('c007','JavaScript','t002');  
insert into course values ('c008','DIV+CSS','t001');  
insert into course values ('c009','PHP','t003');  
insert into course values ('c010','EJB3.0','t002');  
/***************初始化成绩表***********************/  
insert into sc values ('s001','c001',78.9);  
insert into sc values ('s002','c001',80.9);  
insert into sc values ('s003','c001',81.9);  
insert into sc values ('s004','c001',60.9);  
insert into sc values ('s001','c002',82.9);  
insert into sc values ('s002','c002',72.9);  
insert into sc values ('s003','c002',81.9);  
insert into sc values ('s001','c003','59');  
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表结构展示:

• 学生表
  

• 教师表
  

• 课程表
  

• 成绩表
  

二、MySql语句

查询“c001”课程比“c002”课程成绩高的所有学生的学号；

select a.* from
 (select * from sc a where a.cno='c001') a,
 (select * from sc b where b.cno='c002') b
 where a.sno=b.sno and a.score > b.score;
 或
select * from sc a
 where a.cno='c001' 
 and  exists(select * from sc b where b.cno='c002' and a.score>b.score and a.sno = b.sno)

如果exists里面返回的结果行数大于1，则返回true，则外面的查询数据可以返回。
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查询平均成绩大于60 分的同学的学号和平均成绩；

select sno,avg(score) from sc  group by sno having avg(score)>60;
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查询所有同学的学号、姓名、选课数、总成绩；

select a.*,s.sname from
 (select sno,sum(score),count(cno) from sc group by sno) a ,student s where a.sno=s.sno;
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查询姓“刘”的老师的个数；

select count(*) from teacher where tname like '刘%';
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查询没学过“谌燕”老师课的同学的学号、姓名；

select a.sno,a.sname from student a where a.sno not in
(
 select distinct s.sno from sc s,
      (
       select c.* from course c ,
           (select tno from teacher t where tname='谌燕') t
       where c.tno=t.tno
      ) b
  where s.cno = b.cno 
);
或
select st.sno,st.sname from student st where st.sno not in
(
 select distinct sno from sc s 
 join course c on s.cno=c.cno
 join teacher t on c.tno=t.tno where tname='谌燕'
)
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查询学过“c001”并且也学过编号“c002”课程的同学的学号、姓名；

select st.sno,st.sname from student st
 join sc a on st.sno=a.sno
 join sc b on st.sno=b.sno
 where a.cno='c002' and b.cno='c001' and a.score < b.score;

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查询所有课程成绩小于60 分的同学的信息及分数；

select st.*,s.score from student st
 join sc s on st.sno=s.sno
 join course c on s.cno=c.cno
 where s.score <60;
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查询没有学全所有课的同学的学号、姓名；

select stu.sno,stu.sname,count(sc.cno) from student stu
 left join sc on stu.sno=sc.sno
 group by stu.sno,stu.sname
 having count(sc.cno)<(select count(distinct cno)from course);
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查询至少有一门课与学号为“s001”的同学所学相同的同学的学号和姓名；

select st.* from student st,
 (select distinct a.sno from
  (select * from sc) a,
  (select * from sc where sc.sno='s001') b
  where a.cno=b.cno
 ) h
 where st.sno=h.sno and st.sno<>'s001'
 //<>表示!=
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! 把“SC”表中“谌燕”老师教的课的成绩都更改为此课程的平均成绩；

“谌燕”老师教的课的平均成绩：

  select avg(sc.score)  from course a,teacher b ,sc
  where a.tno=b.tno and b.tname='谌燕' and a.cno=sc.cno 
  group by sc.cno
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有问题：把“SC”表中“谌燕”老师教的课的成绩都更改为此课程的平均成绩；

update sc c set score=
 (
  select avg(c.score)  from course a,teacher b 
  where a.tno=b.tno and b.tname='谌燕' and a.cno=c.cno 
  group by c.cno
 )
where cno in( select cno from course a,teacher b where a.tno=b.tno and b.tname='谌燕')
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!查询和“s001”号的同学学习的课程完全相同的其他同学学号和姓名；

删除学习“谌燕”老师课的SC 表记录:

delete from sc where sc.cno in
(
 select cno from course c
 left join teacher t on  c.tno=t.tno
 where t.tname='谌燕'
)
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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 cno ,max(score),min(score) from sc group by cno;
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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 cno,avg(score),sum(case when score>=60 then 1 else 0 end)/count(*) as 及格率
from sc group by cno
order by avg(score) , 及格率 desc
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查询不同老师所教不同课程平均分从高到低显示

再加点数据

select t.tno,t.tname,c.cno,c.cname,c.cno,avg(score) from sc , course c,teacher t
where sc.cno=c.cno and c.tno=t.tno
group by c.cno
order by avg(score) desc;
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统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]

select sc.cno,c.cname,
sum(case  when score between 85 and 100 then 1 else 0 end) AS "[100-85]",
sum(case  when score between 70 and 85 then 1 else 0 end) AS "[85-70]",
sum(case  when score between 60 and 70 then 1 else 0 end) AS "[70-60]",
sum(case  when score <60 then 1 else 0 end) AS "[<60]"
from sc, course c
where  sc.cno=c.cno
group by sc.cno;
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! 查询各科成绩前三名的记录:(不考虑成绩并列情况)

select * from
(select sno,cno,score,row_number()over(partition by cno order by score desc) rn from sc) h
where rn<4
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查询每门课程被选修的学生数

select cno,count(sno)from sc group by cno;
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查询出只选修了一门课程的全部学生的学号和姓名

select sc.sno,st.sname,count(cno) from student st
left join sc
on sc.sno=st.sno
group by st.sname,sc.sno having count(cno)=1;
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查询男生、女生人数

select ssex,count(*)from student group by ssex;
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查询姓“张”的学生名单

select * from student where sname like '张%';
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查询同名同性学生名单，并统计同名人数

select sname,count(*)from student group by sname having count(*)>1;
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1981 年出生的学生名单

select sno,sname,sage,ssex from student t where sage =1981;
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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 cno,avg(score) from sc group by cno order by avg(score)asc,cno desc;
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查询平均成绩大于85 的所有学生的学号、姓名和平均成绩

select st.sno,st.sname,avg(score) from student st
left join sc on sc.sno=st.sno
group by st.sno,st.sname having avg(score)>85;
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查询课程名称为“数据库”，且分数低于60 的学生姓名和分数

select sname,score from student st,sc,course c
where st.sno=sc.sno and sc.cno=c.cno and c.cname='Oracle' and sc.score<60;
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查询所有学生的选课情况；

select st.sno,st.sname,c.cname from student st,sc,course c
where sc.sno=st.sno and sc.cno=c.cno;
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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；

select st.sname,c.cname,sc.score from student st,sc,course c
where sc.sno=st.sno and sc.cno=c.cno and sc.score>70;
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查询不及格的课程，并按课程号从大到小排列

select sc.sno,c.cname,sc.score from sc,course c
where sc.cno=c.cno and sc.score<60 order by sc.cno desc;
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查询课程编号为c001 且课程成绩在80 分以上的学生的学号和姓名；

select st.sno,st.sname,sc.score from sc,student st
where sc.sno=st.sno and cno='c001' and score>80;
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求选了课程的学生人数

select count(distinct sno) from sc;
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查询选修“谌燕”老师所授课程的学生中，成绩最高的学生姓名及其成绩

select st.sname,score from student st,sc ,course c,teacher t
where
st.sno=sc.sno and sc.cno=c.cno and c.tno=t.tno and t.tname='谌燕' and sc.score=
(select max(score)from sc where sc.cno=c.cno)
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查询各个课程及相应的选修人数

select cno,count(sno) from sc group by cno;
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查询不同课程成绩相同的学生的学号、课程号、学生成绩

select a.* from sc a ,sc b where a.score=b.score and a.cno != b.cno;
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查询每门功课成绩最好的前两名

select * from
(select sno,cno,score from sc group by cno order by score desc) my_rn 
limit 0,2;
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统计每门课程的学生选修人数（超过10 人的课程才统计）。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

select cno,count(sno) from sc 
group by cno having count(sno)>10
order by count(sno) desc,cno asc;
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检索至少选修两门课程的学生学号

select sno from sc group by sno having count(cno)>1;
或
select sno from sc group by sno having count(sno)>1;
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!查询全部学生都选修的课程的课程号和课程名

select distinct(c.cno),c.cname from course c ,sc where sc.cno=c.cno;
或
select cno,cname from course c where c.cno in (select cno from sc group by cno);
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查询没学过“谌燕”老师讲授的任一门课程的学生姓名

select st.sname from student st
where st.sno not in
(select distinct sc.sno from sc,course c,teacher t where sc.cno=c.cno and c.tno=t.tno and t.tname='谌燕');
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查询两门以上不及格课程的同学的学号及其平均成绩

select sno,avg(score)from sc
where sno in
(
 select sno from sc where sc.score<60
 group by sno having count(sno)>1
) group by sno;
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检索“c004”课程分数小于60，按分数降序排列的同学学号

select sno from sc where cno='c004' and score<90 order by score desc;
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删除“s002”同学的“c001”课程的成绩

delete from sc where sno='s002' and cno='c001';
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