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在執行我的doDelete.php，出現此錯誤消息：錯誤消息：不能刪除或更新父行，外鍵約束失敗
「無法刪除或更新父行，外鍵約束失敗（ 。fypbook，約束book_user_key外鍵（id）參考文獻user（id）ON DELETE NO ACTION ON UPDATE NO ACTION）「
刪除查詢：
$queryDelete = "DELETE FROM user WHERE id = $theUserID";
從3個表檢索信息查詢：
$query2 = "SELECT * FROM user,country,book where book.id=user.id AND user.country_id=country.country_id ORDER BY `user`.`id` ASC";
我的「書」和「用戶」表之間的關係是用戶能夠添加一本書。因此，用戶ID被放置在書本表中以識別哪個用戶添加了書。但是，當我想從我的PHP中刪除一個用戶，上面的錯誤信息出現。這是檢索用戶ID以刪除用戶的一個片段。我該如何解決？
<td><form method="post" action="doDelete.php"><input type="hidden" name="theUserID" value="<?php echo $rows['id']; ?>" /><input type="submit" value="Delete" /</form></td>
下面是相關表格
CREATE SCHEMA IF NOT EXISTS `fyp` ;
USE `fyp` ;
-- -----------------------------------------------------
-- Table `fyp`.`country`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `fyp`.`country` ;
CREATE TABLE IF NOT EXISTS `fyp`.`country` (
`country_id` INT NOT NULL AUTO_INCREMENT,
`country` VARCHAR(45) NOT NULL,
PRIMARY KEY (`country_id`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `fyp`.`user`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `fyp`.`user` ;
CREATE TABLE IF NOT EXISTS `fyp`.`user` (
`id` INT NOT NULL AUTO_INCREMENT,
`user_name` VARCHAR(45) NOT NULL,
`password` VARCHAR(45) NOT NULL,
`email_address` VARCHAR(45) NOT NULL,
`date_of_birth` DATE NOT NULL,
`country_id` INT NOT NULL,
`gender_id` INT NOT NULL,
`role_id` INT NOT NULL,
`last_login` TIMESTAMP NULL,
PRIMARY KEY (`id`),
INDEX `fk_user_country1_idx` (`country_id` ASC),
INDEX `fk_user_gender1_idx` (`gender_id` ASC),
INDEX `fk_user_role1_idx` (`role_id` ASC),
CONSTRAINT `user_country_key`
FOREIGN KEY (`country_id`)
REFERENCES `fyp`.`country` (`country_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `user_gender_key`
FOREIGN KEY (`gender_id`)
REFERENCES `fyp`.`gender` (`gender_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `user_role_key`
FOREIGN KEY (`role_id`)
REFERENCES `fyp`.`role` (`role_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `fyp`.`book`
-- -----------------------------------------------------
DROP TABLE IF EXISTS `fyp`.`book` ;
CREATE TABLE IF NOT EXISTS `fyp`.`book` (
`book_id` INT NOT NULL AUTO_INCREMENT,
`title` VARCHAR(45) NOT NULL,
`ISBN` VARCHAR(45) NOT NULL,
`book_desc` VARCHAR(100) NOT NULL,
`year_published` VARCHAR(45) NOT NULL,
`year_of_birth` YEAR NOT NULL,
`image` VARCHAR(45) NULL,
`genre_id` INT NOT NULL,
`publisher_id` INT NOT NULL,
`user_id` INT NOT NULL,
PRIMARY KEY (`book_id`),
INDEX `fk_book_publishers1_idx` (`publisher_id` ASC),
INDEX `fk_book_user1_idx` (`user_id` ASC),
INDEX `fk_book_genre1_idx` (`genre_id` ASC),
CONSTRAINT `book_publishers_key`
FOREIGN KEY (`publisher_id`)
REFERENCES `fyp`.`publishers` (`publisher_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `book_user_key`
FOREIGN KEY (`user_id`)
REFERENCES `fyp`.`user` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `book_genre_key`
FOREIGN KEY (`genre_id`)
REFERENCES `fyp`.`genre` (`genre_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;