定義主鍵約束
prinmary key :不允許爲空,不允許重複
刪除主鍵:alter table table_name drop primary key;
定義主鍵自動增長
auto_increment
定義唯一約束
unique
定義非空約束
not null
定義外鍵約束
constraint ordersid_FK foreign key(ordersid) references orders(id)
主外鍵舉例:
create table husband
(
id int primary key,
name varchar(20),
);
create table wife
(
id int primary key,
name varchar(20),
husband_id int,
constraint husband_id_FK foreign key(husband_id) references husband(id)
);
一對多的關聯關係
多對多的關聯
一對一的關聯