[英]Foreign key in MySql as composite primary key
我有一個名為Shop的數據庫,其中有3個表:
create table usr(
id_usr varchar(20) not null,
primary key(id_usr)
);
create table product(
id_product varchar(20) not null,
id_size varchar(20) not null,
price float(4,2) unsigned,
primary key(id_product,id_size)
);
create table cart(
myUser varchar(20),
mySize varchar(20),
product varchar(20),
qty int not null,
primary key(myUser,product,mySize),
FOREIGN KEY (myUser) REFERENCES usr (id_usr),
FOREIGN KEY (product) REFERENCES product (id_product),
FOREIGN KEY (mySize) REFERENCES product (id_size)
);
當我在sql中編譯時,它給我以下消息:
如果我嘗試刪除外鍵mySize(FOREIGN KEY(mySize)參考prodotto(id_size)),它可以工作,為什么我會收到此消息?
您正在對product
表進行FK引用,但僅定義了一部分鍵。 嘗試...
FOREIGN KEY (product, mySize) REFERENCES product (id_product, id_size),
我的猜測是您尚未創建prodotto
表。 這有效:
create table user(
id_user varchar(20) not null,
primary key(id_user)
);
create table product(
id_product varchar(20) not null,
id_size varchar(20) not null,
price float(4,2) unsigned,
primary key(id_product,id_size)
);
create table prodotto (
id_size varchar(20) primary key
);
create table cart(
myUser varchar(20),
mySize varchar(20),
product varchar(20),
qty int not null,
primary key(myUser,product,mySize),
FOREIGN KEY (myUser) REFERENCES user (id_user),
FOREIGN KEY (product) REFERENCES product (id_product),
FOREIGN KEY (mySize) REFERENCES prodotto (id_size)
);
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