一对多
create table press( id int primary key auto_increment, name varchar(20));create table book( id int primary key auto_increment, name varchar(20), press_id int not null, constraint fk_book_press foreign key(press_id) references press(id) on delete cascade on update cascade);# 先往被关联表中插入记录insert into press(name) values('北京工业地雷出版社'),('人民音乐不好听出版社'),('知识产权没有用出版社');# 再往关联表中插入记录insert into book(name,press_id) values('九阳神功',1),('九阴真经',2),('九阴白骨爪',2),('独孤九剑',3),('降龙十巴掌',2),('葵花宝典',3);查询结果：mysql> select * from book;+----+-----------------+----------+| id | name | press_id |+----+-----------------+----------+| 1 | 九阳神功 | 1 || 2 | 九阴真经 | 2 || 3 | 九阴白骨爪 | 2 || 4 | 独孤九剑 | 3 || 5 | 降龙十巴掌 | 2 || 6 | 葵花宝典 | 3 |+----+-----------------+----------+rows in set (0.00 sec)mysql> select * from press;+----+--------------------------------+| id | name |+----+--------------------------------+| 1 | 北京工业地雷出版社 || 2 | 人民音乐不好听出版社 || 3 | 知识产权没有用出版社 |+----+--------------------------------+rows in set (0.00 sec)
多对多
# 创建被关联表author表，之前的book表在多对一的关系已创建create table author( id int primary key auto_increment, name varchar(20));#这张表就存放了author表和book表的关系，即查询二者的关系查这表就可以了create table author2book( id int not null unique auto_increment, author_id int not null, book_id int not null, constraint fk_author foreign key(author_id) references author(id) on delete cascade on update cascade, constraint fk_book foreign key(book_id) references book(id) on delete cascade on update cascade, primary key(author_id,book_id));#插入四个作者，id依次排开insert into author(name) values('qwe'),('asd'),('zxc'),('wer');# 每个作者的代表作qwe: 九阳神功、九阴真经、九阴白骨爪、独孤九剑、降龙十巴掌、葵花宝典asd: 九阳神功、葵花宝典zxc:独孤九剑、降龙十巴掌、葵花宝典wer:九阳神功# 在author2book表中插入相应的数据insert into author2book(author_id,book_id) values(1,1),(1,2),(1,3),(1,4),(1,5),(1,6),(2,1),(2,6),(3,4),(3,5),(3,6),(4,1);# 现在就可以查author2book对应的作者和书的关系了mysql> select * from author2book;+----+-----------+---------+| id | author_id | book_id |+----+-----------+---------+| 1 | 1 | 1 || 2 | 1 | 2 || 3 | 1 | 3 || 4 | 1 | 4 || 5 | 1 | 5 || 6 | 1 | 6 || 7 | 2 | 1 || 8 | 2 | 6 || 9 | 3 | 4 || 10 | 3 | 5 || 11 | 3 | 6 || 12 | 4 | 1 |+----+-----------+---------+rows in set (0.00 sec)
一对一
#例如： 一个用户只能注册一个博客#两张表： 用户表 （user）和 博客表(blog)# 创建用户表create table user( id int primary key auto_increment, name varchar(20));# 创建博客表create table blog( id int primary key auto_increment, url varchar(100), user_id int unique, constraint fk_user foreign key(user_id) references user(id) on delete cascade on update cascade);#插入用户表中的记录insert into user(name) values('qwe'),('asd'),('zxc'),('ert');# 插入博客表的记录insert into blog(url,user_id) values('http://www.cnblog/qwe',1),('http://www.cnblog/asd',2),('http://www.cnblog/zxc',3),('http://www.cnblog/ert',4);# 查询wusir的博客地址select url from blog where user_id=2;