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MySQL 創(chuàng)建多對(duì)多和一對(duì)一關(guān)系方法

 更新時(shí)間：2022年03月24日 16:38:27   作者：江下下啊  
這篇文章主要介紹了MySQL 創(chuàng)建多對(duì)多和一對(duì)一關(guān)系方法，文章舉例詳細(xì)說明具有一定的參考價(jià)值，需要的小伙伴可以參考一下

一、創(chuàng)建多對(duì)多

1.學(xué)生表

create table students (
??
id int not null primary key auto_increment,
??
name varchar(45) not null
??
)engine=innodb default charset=utf8;

2.課程表

create table courses (
??
id int not null primary key auto_increment,
??
name varchar(45) not null?
??
)engine=innodb default charset=utf8;

3.中間表

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.插入數(shù)據(jù)

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,"語文");
insert into courses values (0,"數(shù)學(xué)");
insert into courses values (0,"英語");


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.查詢學(xué)生1選了哪些科目

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.查詢id=2數(shù)學(xué)被誰選了

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 創(chuàng)建一對(duì)一關(guān)系

1.一對(duì)一

創(chuàng)建用戶表：

CREATE TABLE users (

id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,

name VARCHAR(50) NOT NULL

)ENGINE=InnoDB DEFAULT CHARSET=utf8;

用戶信息表：

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.插入數(shù)據(jù)

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);

查詢?nèi)说娜啃畔ⅲ?/strong>

select * from users inner join users_info on
users_info.user_id =users.id;

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