=====================多對一=====================
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,
foreign key(press_id) references press(id)
on delete cascade
on update cascade
);


insert into press(name) values
(
 
'北京工業地雷出版社'),
('人民音樂不好聽出版社'),
('智慧財產權沒有用出版社')
;

insert into book(name,press_id) values
('九陽神功',1),
('九陰真經',2),
('九陰白骨爪',2),
('獨孤九劍',3),
('降龍十巴掌',2),
('葵花寶典',3)
;

sql示例

create table author(
id int primary key auto_increment,
name varchar(20)
);


#這張表就存放作者表與書表的關係，即查詢二者的關係查這表就可以了
 

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)
);


 
#插入四個作者，id依次排開
insert into author(name) values('egon'),('alex'),('yuanhao'),('wpq');

#每個作者與自己的代表作如下
egon: 
九陽神功
九陰真經
九陰白骨爪
獨孤九劍
降龍十巴掌
葵花寶典
alex: 
九陽神功
葵花寶典
yuanhao:
獨孤九劍
降龍十巴掌
葵花寶典
wpq:
九陽神功


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)
;

sql示例

create table customer(
    -> id int primary key auto_increment,
    -> name varchar(20) not null,
    -> qq varchar(10) not null,
    -> phone char(16) not null
    -> );

create table student(
    -> id int primary key auto_increment,
    -> class_name varchar(20) not null,
    -> customer_id int unique, #該欄位一定要是唯一的
    -> foreign key(customer_id) references customer(id) #外來鍵的欄位一定要保證unique
    -> on delete cascade
    -> on update cascade
    -> );

#增加客戶
mysql> insert into customer(name,qq,phone) values
    -> ('韓蕾','31811231',13811341220),
    -> ('楊瀾','123123123',15213146809),
    -> ('翁惠天','283818181',1867141331),
    -> ('楊宗河','283818181',1851143312),
    -> ('袁承明','888818181',1861243314),
    -> ('袁清','112312312',18811431230)

mysql> #增加學生
mysql> insert into student(class_name,customer_id) values
    -> ('脫產1班',3),
    -> ('週末1期',4),
    -> ('週末1期',5)
    -> ;

sql示例