SQL外鍵

Question

我在讀一本關於電子商務的書。在這本書中，我發現瞭如下因素的SQL代碼：

CREATE TABLE `orders` (
    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT, 
    `users_id` INT UNSIGNED NOT NULL, 
    `transaction_id` VARCHAR(45) NOT NULL, 
    `payment_status` VARCHAR(45) NOT NULL, 
    `payment_amount` INT UNSIGNED NOT NULL, 
    `date_created` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP, 
    PRIMARY KEY (`id`), 
    INDEX `date_created` (`date_created` ASC), 
    INDEX `transaction_id` (`transaction_id` ASC), 
    CONSTRAINT `fk_orders_users1` 
     FOREIGN KEY (`id`) 
     REFERENCES `users` (`id`) 
     ON DELETE NO ACTION 
     ON UPDATE NO ACTION 
) ENGINE = InnoDB DEFAULT CHARSET=utf8; 

書上說，該約束將防止出現「users_id」不匹配表中的「用戶」一個「身份證」的插入。通過閱讀代碼，我相信這本書是錯誤的，因爲我相信這段代碼會阻止插入一個「id」（在表中的「orders」），它與字段「id」不匹配）。我是對的？

對不起，英語不好。我不是美國人，並盡我所能...

Answer 1

更正代碼：

CREATE TABLE `orders` (
    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT, 
    `users_id` INT UNSIGNED NOT NULL, 
    `transaction_id` VARCHAR(45) NOT NULL, 
    `payment_status` VARCHAR(45) NOT NULL, 
    `payment_amount` INT UNSIGNED NOT NULL, 
    `date_created` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP, 
    PRIMARY KEY (`id`), 
    INDEX `date_created` (`date_created` ASC), 
    INDEX `transaction_id` (`transaction_id` ASC), 
    CONSTRAINT `fk_orders_users1` 
     FOREIGN KEY (`users_id`) 
     REFERENCES `users` (`id`) 
     ON DELETE NO ACTION 
     ON UPDATE NO ACTION 
) ENGINE = InnoDB DEFAULT CHARSET=utf8;