准备工作

创建student表

CREATE  TABLE student (
id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY ,
name  VARCHAR(20)  NOT NULL ,
sex  VARCHAR(4) ,
birth  YEAR,
department  VARCHAR(20) ,
address  VARCHAR(50)
);

创建score表

CREATE  TABLE score (
id  INT(10)  NOT NULL  UNIQUE  PRIMARY KEY  AUTO_INCREMENT ,
stu_id  INT(10)  NOT NULL ,
c_name  VARCHAR(20) ,
grade  INT(10)
);

向student表插入数据

INSERT INTO student VALUES(901,'张老大','男',1985,'计算机系','北京市海淀区');
INSERT INTO student VALUES(902,'张老二','男',1986,'中文系','北京市昌平区');
INSERT INTO student VALUES(903,'张三','女',1990,'中文系','湖南省永州市');
INSERT INTO student VALUES(904,'李四','男',1990,'英语系','辽宁省阜新市');
INSERT INTO student VALUES(905,'王五','女',1991,'英语系','福建省厦门市');
INSERT INTO student VALUES(906,'王六','男',1988,'计算机系','湖南省衡阳市');

向score表插入数据

INSERT INTO score VALUES(NULL,901, '计算机',98);
INSERT INTO score VALUES(NULL,901, '英语', 80);
INSERT INTO score VALUES(NULL,902, '计算机',65);
INSERT INTO score VALUES(NULL,902, '中文',88);
INSERT INTO score VALUES(NULL,903, '中文',95);
INSERT INTO score VALUES(NULL,904, '计算机',70);
INSERT INTO score VALUES(NULL,904, '英语',92);
INSERT INTO score VALUES(NULL,905, '英语',94);
INSERT INTO score VALUES(NULL,906, '计算机',90);
INSERT INTO score VALUES(NULL,906, '英语',85);

练习开始

1.查询student表的所有记录

select  * from student; 

2.查询student表的第2条到4条记录

select * from student limit 1,3;

3.从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息

select id 学号, name 姓名, department 院系 from student;

4.从student表中查询计算机系和英语系的学生的信息

select id 学号, name 姓名, sex 性别, birth 出生日期, department 院系, address 地址 from student 
where department = '计算机系' or department = '英语系';

5.从student表中查询年龄18~22岁的学生信息

select stu1.id 学号,stu1.name 姓名,stu1.sex 性别,stu1.birth,stu2.age 年龄
from student stu1 
right join(select id ,2010-`birth` age from student) as stu2 
on stu1.id = stu2.id
where stu2.age between 18 and 22;

6.从student表中查询每个院系有多少人

select department 院系,count(id) 人数 from student group by department;

7.从score表中查询每个科目的最高分

select c_name 科目, max(grade) 最高分 from score group by c_name;

8.查询李四的考试科目（c_name）和考试成绩（grade）

select sc.c_name 考试科目, sc.grade 考试成绩 from score sc
right join student stu
on sc.stu_id = stu.id
where stu.name = '李四';

9.用连接的方式查询所有学生的信息和考试信息

select stu.id 学号,stu.name 姓名,stu.sex 性别, stu.birth 出生日期,stu.address 地址,sc.c_name 科目,sc.grade 分数 from student stu 
inner join score sc 
on stu.id = sc.stu_id ;

10.计算每个学生的总成绩

select stu.name 姓名, sum(sc.grade) 总分 from student stu 
inner join score sc 
on stu.id = sc.stu_id
group by sc.stu_id;

11.计算每个考试科目的半均成绩

select c_name 科目, avg(grade) from score group by c_name;

12.查询计算机成绩低于95的学生信息

select stu.id 学号,stu.name 姓名, stu.sex 性别, stu.department 院系,sc.c_name 科目,sc.grade from student stu
left join score sc
on stu.id = sc.stu_id
where sc.c_name = '计算机' having grade < 95;

13.查询同时参加计算机和英语考试的学生的信息

select stu.id, stu.name, stu.department from student stu
left join  (select * from score where c_name in ('计算机','英语')) as stu1
on stu.id = stu1.stu_id
group  by  id having count(name) = 2;

14.将计算机考试成绩按从高到低进行排序

select  grade from score where c_name = '计算机' order by grade desc;

15.从student表和score表中查询出学生的学号，然后合并查询结果

select * from (
select id from student
union
select stu_id from score
) id_tb;

16.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩

select stu.name 姓名,stu.department 院系, sc.c_name 考试科目,sc.grade 成绩 from student stu
inner join score sc
on stu.id = sc.stu_id
where stu.name like '张%' or stu.name like '王%';

17.查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩

select stu.name 姓名, stu2.age 年龄 ,stu.department 院系, stu2.c_name 考试科目, stu2.grade 成绩 from student stu
inner join (select stu1.id,stu1.age , sc.c_name , sc.grade  from score sc 
left join (select id,2010-`birth` as age from student) as stu1 
on sc.stu_id = stu1.id ) as stu2
on  stu.id = stu2.id
where stu.address like '湖南%';