MySQL 创建多对多和一对一关系方法
作者：江下下啊
这篇文章主要介绍了MySQL 创建多对多和一对一关系方法，文章举例详细说明具有一定的参考价值，需要的小伙伴可以参考一下
一、创建多对多
1.学生表
create table students ( id int not null primary key auto_increment, name varchar(45) not null )engine=innodb default charset=utf8;
2.课程表
create table courses ( id int not null primary key auto_increment, name varchar(45) not null )engine=innodb default charset=utf8;
3.中间表
create table stu_cour ( id int not null primary key auto_increment course_id int not null, stu_id int not null, constraint cour foreign key(course_id) references courses(id), constraint stu foreign key(stu_id) references students(id) )engine=innodb default charset=utf8;
4.插入数据
insert into students values (0,"小王"); insert into students values (0,"小宋"); insert into students values (0,"小李"); insert into courses values (0,"语文"); insert into courses values (0,"数学"); insert into courses values (0,"英语"); insert into stu_cour values (0,1,1); insert into stu_cour values (0,1,2); insert into stu_cour values (0,1,3); insert into stu_cour values (0,2,1); insert into stu_cour values (0,2,3); insert into stu_cour values (0,3,2); insert into stu_cour values (0,3,3);
5.查询学生1选了哪些科目
SELECT courses.id,courses.name FROM courses INNER JOIN stu_cour ON stu_cour.course_id=courses.id INNER JOIN students ON students.id= 1 and students.id = stu_cour.stu_id;
6.查询id=2数学被谁选了
SELECT students.name FROM students INNER JOIN stu_cour ON stu_cour.stu_id =students.id INNER JOIN courses ON courses.id= 2 and stu_cour.course_id = courses.id;
二、MySQL 创建一对一关系
1.一对一
创建用户表：
CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, name VARCHAR(50) NOT NULL )ENGINE=InnoDB DEFAULT CHARSET=utf8;
用户信息表：
CREATE TABLE users_info ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, age int NOT NULL, phone varchar(11) NOT NULL, user_id int not null, constraint user_info foreign key(user_id) references users(id) )ENGINE=InnoDB DEFAULT CHARSET=utf8;
2.插入数据
insert into users values (0,"小王"); insert into users values (0,"小宋"); insert into users_info values (0,12,'13812345678',1); insert into users_info values (0,14,'13812345679',2);
查询人的全部信息：
select * from users inner join users_info on users_info.user_id =users.id;
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