数据库MySQL----多表查询

二、多表查询

1.创建student和score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)
);
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)
);
2.为student表和score表增加记录
向student表插入记录的INSERT语句如下：

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表插入记录的INSERT语句如下：

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);
3.查询student表的所有记录

select * from student;

student表的第2条到4条记录

select * from student limit 1,3;

5.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,name,department from student;

6.从student表中查询计算机系和英语系的学生的信息

select * from student where department in ('计算机系','英语系');

7.从student表中查询年龄28~32岁的学生信息

select * from student where 2013-birth between 28 and 32;

8.从student表中查询每个院系有多少人

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

9.从score表中查询每个科目的最高分

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

10.查询李四的考试科目（c_name）和考试成绩（grade）

select c_name,grade from score where stu_id=(select id from student where name='李四');

11.用连接的方式查询所有学生的信息和考试信息

select * from student,score where student.id=score.stu_id;

12.计算每个学生的总成绩

select student.id,name,sum(grade) from student,score where student.id=score.stu_id group by id;

13.计算每个考试科目的平均成绩

select student.id,name,avg(grade) from student,score where student.id=score.stu_id group by id;

14.查询计算机成绩低于95的学生信息

select * from student where id in (select stu_id from score where c_name='计算机' and grade < 95);

15.查询同时参加计算机和英语考试的学生的信息

select * from student where id = any
-> (select stu_id from score
-> where stu_id in (
-> select stu_id from
-> score where c_name='计算机')
-> and c_name='英语');