数据库练习题（学生课程表）

创建表

DROP TABLE IF EXISTS student;
CREATE TABLE student(
sno int auto_increment primary key,
sname varchar(8),
ssex varchar(3),
sage int ,
sclass varchar(6)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO student(sname,ssex,sage,sclass) VALUES('李勇','男',20,'y01');
INSERT INTO student(sname,ssex,sage,sclass) VALUES('刘晨','男',21,'y02');
INSERT INTO student(sname,ssex,sage,sclass) VALUES('王敏','女',19,'y02');
INSERT INTO student(sname,ssex,sage,sclass) VALUES('张力','男',25,'y05');

DROP TABLE IF EXISTS course;
CREATE TABLE course(
cno int auto_increment primary key,
cname varchar(20),
ccredit int
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO course(cname,ccredit) VALUES('C语言',5);
INSERT INTO course(cname,ccredit) VALUES('数据库',5);
INSERT INTO course(cname,ccredit) VALUES('开发模式_VB',5);

DROP TABLE IF EXISTS sc;
CREATE TABLE sc(
sno int references student(sno) on delete cascade,
cno int references course(cno) on delete cascade,
grade int
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO sc VALUES(1,1,90);
INSERT INTO sc VALUES(1,2,95);
INSERT INTO sc VALUES(2,1,55);
INSERT INTO sc VALUES(4,3,null);

练习加总结：

			
1、查出全体同学的学号、姓名
select sno,sname from student;
2、查询全体同学的姓名学号班级（按顺序输出）
select sname,sno,sclass from student;
3、查询全体同学的记录（显示所有行）
select * from student;
4、查询全体同学的姓名及出生年份
select sname,(2010-sage) as '出生年份' from student ;
5、查询全体同学姓名出生年份班级（班级要用小写字母lower函数）
select sname,2010-sage as '出生年份',lower(sclass) from student;
6、查询全体同学的姓名/出生年份/所在班级列为YearOfBirth
select sname,2010-sage YearOfBirth,sclass from student;
7、查询选中学员的所在班级并且去掉重复行用distinct
select distinct sclass from student;
8、查询Y02班全体同学名单
select * from student where sclass='y02';
9、查询所有年龄在20岁一下的同学姓名及年龄
select sname,sage from student where sage<20;
10、查询考试不及格的同学的姓名及成绩
select s.sname,sc.grade from student s,sc where s.sno = sc.sno and sc.grade <60;
11、查询年龄在19－20岁（包括19、20）之间的同学姓名、班级、年龄
select sname,sclass,sage from student where sage in (19,20);（19、20 比较特殊选项少可以使用 in）
select sname,sclass,sage from student where sage between 19 and 20;
select sname,sclass,sage from student where sage>=19 and sage<=20;
12、查询年龄不在19－20岁之间的同学姓名、班级、年龄
select sname,sclass,sage from student where sage not in (19,20);
select sname,sclass,sage from student where sage not between 19 and 20;
select sname,sclass,sage from student where sage<19 or sage>20;
13、查询y02班级和y05班的同学的姓名、性别
select sname,sclass from student where sclass in ('y02','y05');
select sname,sclass from student where sclass='y02' or sclass='y05';
14、查询不是y02或者y05班的同学的姓名、性别
select sname,sage from student where sclass not in('y02','y05');
select sname,sage from student where sclass!='y02' and sclass!='y05';
select sname,sage from student where not sclass='y02' and not sclass='y05';
15、查所有姓刘的同学的姓名、学号、性别( " % "表示一个或者多个，" _ "表示只占一个字符)
select sname,sno,ssex from student where sname like'刘%';
16、查所有姓张且全名只有2个汉子的同学的所有信息
select * from student where sname like'张_';
17、某些学生未考试查缺成绩的同学的学号和课程号
select sno,cno,grade from sc where grade is null;
18、查询所有成绩的同学的学号、课程号和成绩
select sno,cno,grade from sc where grade is not null;
19、查y02班年龄在20岁一下的姓名和年龄
select sname,sage from student where sclass='y02' and sage<20;
20、查选修1号课程的同学的学号和成绩，按成绩降序排序
select sno,grade from sc where cno=1 order by grade desc;
21、查全体同学信息查询结果按所在班级的班级名称按降序排列，同班同学按年龄升序排列
select * from student order by sclass desc,sage asc; 
22、查询学员的总人数
select count(sno) from student; 
23、查选修课程学院人数
select count(*) from sc;
24、统计1号课的学院平均成绩
select avg(grade) 平均成绩 from sc where cno=1;
25、查选修1号课和同学最高成绩
select max(grade) from sc where cno=1;
26、求各个课程号及相应选课人数
select cno,count(*) 选课人数 from sc group by cno;
27、查选取1门以上课程的同学学号和课程个数
select sno,count(cno) from sc group by sno having count(cno)>1;
28、查每个学员及其选修课程情况
select sno,cno from sc;
29、查每个学员及其选修课程情况对没有选课的也要输出其姓名、学号、性别、班级(注意：是作外连接student是主表)
select st.sname,st.sno,st.ssex,st.sclass,sc.cno,sc.grade 
from student st left join sc on
st.sno = sc.sno order by st.sname;
30、查选取2号课程且成绩在90分以上的同学
select * from sc where cno=2 and grade>90;
31、查询每个同学学号姓名，选课程名称及其成绩
select stu.sno,stu.sname,c.cname,sc.grade
from student stu join sc on stu.sno = sc.sno
join course c on c.cno = sc.cno;
或者
select stu.sno,stu.sname,c.cname,sc.grade
from student stu,course c,sc
where stu.sno=sc.sno and c.cno= sc.cno
order by sc.cno  desc;
32、查与刘晨在一个班的同学
select * from student where sclass=(select sclass from student where sname='刘晨');
33、选取C语言的同学学号和姓名
select s.sno,s.sname 
from student s join sc on s.sno=sc.sno
join course c on sc.cno=c.cno
where c.cname='C语言';
或者
select sno,sname from student where sno in 
(select sno from sc where cno in
(select cno from course where cname='C语言'));
34、查其他班级中比y02班某一同学大的同学姓名和年龄
select sname,sage from student
where sclass<>'y02' and
sage > (select min(sage) from student where sclass='y02');
或者（加入 any 关键字）
select sname,sage from student
where sclass<>'y02' and
sage >any (select sage from student where sclass='y02');
35、查其他班中比y02班同学全部都大的同学姓名和年龄
select sname,sage from student
where sclass!='y02' and
sage > (select max(sage) from student where sclass='y02');
或者（加入 all 关键字）
select sname,sage from student
where sclass!='y02' and
sage >all (select sage from student where sclass='y02');
36、查选取1号课程的学员的姓名
（在与查询的集合的包含关系时，最好使用 in 、any、all）
select s.sname from student s,sc
where s.sno = sc.sno and sc.cno=1;
或者（子查询）
select sname from student where sno in
(select sno from sc where cno=1);
37、查没有选取1号课程的学员的姓名(注意：要过滤已经选取过1号的同学，因为可能某同学多选修课程)
说明：如果是过滤集合，就只能用 in/all/any
select sname from student where sno not in
(select sno from sc where cno=1);
38、查y02班同学及年龄不大于19岁的学员（union）
select * from student where sclass='y02' union
select * from student where sage<=19;
解析：y02班级的同学与全年纪年龄不大于19岁的学生，而（sage<=19 and sclass='y02'）表示为
y02班级同学“且”年龄不大于19岁的同学，与题意不符。所以下面的语句是错误的，因为范围没有确定好
select * from student where sclass='y02' and sage<=19;
说明：union 用来两个集合求并集（合并两个集合，并且除去重复的记录）
39、查询选取1号课程或者2号课程的同学学号
select distinct sno from sc where  cno=1 or cno=2;
或者
select distinct sno from sc where cno in (1,2);
40、将4号学员的年龄改为23岁
update student set sage=23 where sno=4;
41、将所有同学的年龄增加1岁
update student set sage=sage+1;
42、y02班的同学的成绩改为100
update sc set grade=100 where sno in (select sno from student where sclass='y02');
43、删除学号为1的同学记录
delete from student where sno=1;