mysql - 无法添加外键约束错误:

Question

我不明白为什么 mysql 工作台会显示
无法添加外键约束错误:该错误显示在 Sales_Order 和 Purchase_Order 表中。我无法弄清楚可能是什么问题。我已经创建了 Er 图，但无法在 sql 工作台中运行。

/* 删除现有表*/

DROP TABLE IF EXISTS Sales_Order; 
DROP TABLE IF EXISTS Purchase_Order; 
DROP TABLE IF EXISTS Supplier;
DROP TABLE IF EXISTS Book; 
DROP TABLE IF EXISTS Customer; 

/* Creating the full sets of Table */

/*Customer Table*/
CREATE TABLE Customer(
Customer_ID INTEGER NOT NULL, 
Customer_Name VARCHAR(255) NOT NULL, 
Customer_Address VARCHAR(255) NOT NULL, 
Customer_Purchase VARCHAR(50) NOT NULL,
Customer_Phone VARCHAR(100) NOT NULL,
CONSTRAINT PKCustomer_ID PRIMARY KEY (Customer_ID)
);

/*Book Table*/
CREATE TABLE Book(
Book_ID  INTEGER NOT NULL,
Book_Name VARCHAR(255) NOT NULL, 
Book_Qty INTEGER NOT NULL, 
Book_Price DECIMAL NOT NULL, 
Book_Author VARCHAR(255) NOT NULL, 
Book_Publisher VARCHAR(255) NOT NULL,
CONSTRAINT PKBook_ID PRIMARY KEY(Book_ID)
);





/*Supplier Table*/
CREATE TABLE Supplier(
Supplier_ID INTEGER NOT NULL,
Supplier_Name VARCHAR(255) NOT NULL, 
Supplier_Address VARCHAR(255) NOT NULL,
CONSTRAINT PKSupplier_ID PRIMARY KEY (Supplier_ID)
); 



/*Sales_Order Table*/
CREATE TABLE Sales_Order(
Sales_ID INTEGER NOT NULL,
Sales_Date INTEGER(20) NOT NULL, 
Sale_Qty INTEGER NOT NULL, 
Discount INTEGER NOT NULL,
CONSTRAINT PKSales_ID PRIMARY KEY (Sales_ID),
CONSTRAINT FKSales_ID FOREIGN KEY (Sales_ID) REFERENCES Customer(Customer_ID),
CONSTRAINT FKSales_ID FOREIGN KEY (Sales_ID) REFERENCES Book(Book_ID)
);

/*Purchase_Table Table*/
CREATE TABLE Purchase_Order(
Purchase_Order_ID INTEGER NOT NULL,
Purchase_Date INTEGER NOT NULL,
Purchase_Description VARCHAR(255) NOT NULL,
Purchase_Qty INTEGER NOT NULL, 
CONSTRAINT PKPurchase_Order_ID PRIMARY KEY (Purchase_Order_ID),
CONSTRAINT FKPurchase_Order_ID FOREIGN KEY(Purchase_Order_ID) REFERENCES Book(Book_ID),
CONSTRAINT FKPurchase_Order_ID FOREIGN KEY(Purchase_Order_ID) REFERENCES Supplier(Book_ID)
);

Answer 1

同一个表中的两个外键不能具有相同的名称。

Example- FKSales_ID

因此，更改外键约束之一的名称。