無法添加外鍵約束MySQL Workbench

Question

嘗試創建「訂單」表時，出現「錯誤代碼：1215.無法添加外鍵約束」。

credit_cards表：

CREATE TABLE credit_cards (
    customer VARCHAR(30), 
    card_no CHAR(16), 
    PRIMARY KEY (customer, card_no), 
    FOREIGN KEY (customer) REFERENCES customers(username)); 

訂單表：

CREATE TABLE orders (
    order_no INT AUTO_INCREMENT, 
    customer VARCHAR(30) NOT NULL, 
    date_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP, 
    credit_card CHAR(16) NOT NULL, 
    PRIMARY KEY (order_no), 
    FOREIGN KEY (customer) 
     REFERENCES customers (username), 
    FOREIGN KEY (credit_card) 
     REFERENCES credit_cards (card_no)); 

從SHOW ENGINE INNODB STATUS報告說，這個問題是FOREIGN KEY (credit_card) REFERENCES credit_cards(card_no))

我讀了一堆的解決問題，仍然可以不知道。我正在使用MySQL Workbench。謝謝。

Answer 1

您需要引用全部主鍵（或唯一鍵）關係中的鍵。我建議：

CREATE TABLE credit_cards (
    credit_card_id int auto_increment primary key, 
    customer VARCHAR(30), 
    card_no CHAR(16), 
    UNIQUE KEY (customer, card_no), 
    FOREIGN KEY (customer) REFERENCES customers(username)); 
orders table: 

CREATE TABLE orders (
    order_no INT AUTO_INCREMENT, 
    customer VARCHAR(30) NOT NULL, 
    date_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP, 
    credit_card_id int NOT NULL, 
    PRIMARY KEY (order_no), 
    FOREIGN KEY (customer) 
     REFERENCES customers (username), 
    FOREIGN KEY (credit_card_id) 
     REFERENCES credit_cards (credit_card_id));