當我嘗試向表中添加THIRD外鍵時出現無法添加外鍵約束錯誤

Question

我一直試圖將屬性O_BagelID添加到我的Order表中，但是，每當嘗試將其添加時，都會出現錯誤“無法添加外鍵約束”。

如您所見，我已經確保Order中的外鍵和Bagel中的引用都屬於同一類型。 當我刪除O_BagelID和所有相關字段時，我不再遇到該錯誤。

CREATE TABLE `Order`(
    OrderID INTEGER NOT NULL, 
    O_CustomerID INTEGER NOT NULL,  
    O_BagelCardID VARCHAR(16),
    O_BagelID INTEGER,  
    Order_date DATE NOT NULL, 
    Order_Cost DECIMAL(4,2) NOT NULL,
    Discount_applied BOOLEAN NOT NULL, 
    PRIMARY KEY(OrderID,O_CustomerID,O_BagelCardID,O_BagelID),

    FOREIGN KEY (O_CustomerID) 
    REFERENCES Customer(CustomerID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE,

    FOREIGN KEY (O_BagelCardID) 
    REFERENCES BagelCard(BagelCardID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE,

    FOREIGN KEY (O_BagelID) 
    REFERENCES Bagel(BagelID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE  
);

CREATE TABLE Bagel(
    BagelID INTEGER NOT NULL,
    Contains_Nuts BOOLEAN NOT NULL,
    Price DECIMAL(4,2) NOT NULL, 
    Description VARCHAR(255),
    PRIMARY KEY(BagelID)
);

Answer 1

您應該首先創建表Bagel ，然后創建表Order 。 當您創建對另一個表的引用時，它應該已經存在：

CREATE TABLE Bagel(
    BagelID INTEGER NOT NULL,
    Contains_Nuts BOOLEAN NOT NULL,
    Price DECIMAL(4,2) NOT NULL, 
    Description VARCHAR(255),
    PRIMARY KEY(BagelID)
);

CREATE TABLE `Order`(
    OrderID INTEGER NOT NULL, 
    O_CustomerID INTEGER NOT NULL,  
    O_BagelCardID VARCHAR(16),
    O_BagelID INTEGER,  
    Order_date DATE NOT NULL, 
    Order_Cost DECIMAL(4,2) NOT NULL,
    Discount_applied BOOLEAN NOT NULL, 
    PRIMARY KEY(OrderID,O_CustomerID,O_BagelCardID,O_BagelID),

    FOREIGN KEY (O_CustomerID) 
    REFERENCES Customer(CustomerID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE,

    FOREIGN KEY (O_BagelCardID) 
    REFERENCES BagelCard(BagelCardID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE,

    FOREIGN KEY (O_BagelID) 
    REFERENCES Bagel(BagelID)
    ON DELETE RESTRICT
    ON UPDATE CASCADE  
);