錯誤1215：使用ON刪除時無法添加外鍵約束SET NULL

Question

我試圖在MySQL中創建以下表格。第一招：

CREATE TABLE IF NOT EXISTS address(
    address_id INT NOT NULL AUTO_INCREMENT, 
    address_region VARCHAR(10) NOT NULL, 
    address_country VARCHAR(20) NOT NULL, 
    address_city VARCHAR(30) NOT NULL, 
    PRIMARY KEY(address_id))ENGINE = InnoDB; 

我創造了它成功的，但是當我嘗試創建另一個表如下

CREATE TABLE IF NOT EXISTS spot(
    spot_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, 
    spot_address INT(11) NOT NULL, 
    spot_name VARCHAR(50) NOT NULL, 
    spot_desc VARCHAR(500) DEFAULT ' ', 
    spot_speadd VARCHAR(100) NOT NULL, 
    spot_viewtime INT DEFAULT 0, 
    FOREIGN KEY(spot_address) 
    REFERENCES address(address_id) 
    ON DELETE SET NULL 
    ON UPDATE SET NULL); 

我得到一個錯誤：

ERROR 1215 (HY000): Cannot add foreign key constraint

這是爲什麼創建表陳述失敗？

Answer 1

你必須在spot表上spot_addressNOT NULL約束，然後嘗試將其設置爲NULL在父表address刪除或更新。

Answer 2

你可以試試這個：

CREATE TABLE IF NOT EXISTS address 
(
address_id INT NOT NULL AUTO_INCREMENT, 
address_region VARCHAR(10) NOT NULL, 
address_country VARCHAR(20) NOT NULL, 
address_city VARCHAR(30) NOT NULL, 
PRIMARY KEY(address_id) 
)ENGINE = INNODB; 




CREATE TABLE IF NOT EXISTS `spot` 
(
    `spot_id` INT(11) NOT NULL AUTO_INCREMENT, 
    `spot_address` INT(11) NOT NULL, 
    `spot_name` VARCHAR(50) NOT NULL, 
    `spot_desc` VARCHAR(500) DEFAULT ' ', 
    `spot_speadd` VARCHAR(100) NOT NULL, 
    `spot_viewtime` INT(11) DEFAULT '0', 
    PRIMARY KEY (`spot_id`), 
    KEY `spot_address` (`spot_address`), 
    CONSTRAINT `spot_ibfk_1` FOREIGN KEY (`spot_address`) REFERENCES `address` (`address_id`) 
) ENGINE=INNODB DEFAULT CHARSET=utf8