MySQL如何创建多对多和一对一关系

这篇文章主要介绍"MySQL如何创建多对多和一对一关系"，在日常操作中，相信很多人在MySQL如何创建多对多和一对一关系问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"MySQL如何创建多对多和一对一关系"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

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.idINNER 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.idINNER 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 onusers_info.user_id =users.id;

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