Question

我无法添加外键约束。我正在运行的sql是 -

 ALTER TABLE image_shout ADD CONSTRAINT `fk_image` FOREIGN KEY (image_id) 
REFERENCES images(image_id);

排序规则和数据类型（int（10））在两个表中相同。

mysql说 -

Error Code: 1215. Cannot add foreign key constraint

图像表结构 -

CREATE TABLE `images` (
  `image_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `image_name` varchar(100) CHARACTER SET latin1 NOT NULL,
  `created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `caption` varchar(450) CHARACTER SET latin1 DEFAULT NULL,
  `image_visibility` int(10) unsigned NOT NULL,
  `album_id` int(10) unsigned NOT NULL,
  `album_view` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  `album_thumb_view` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  PRIMARY KEY (`image_id`),
  KEY `Index_2` (`album_id`),
  CONSTRAINT `FK_images_1` FOREIGN KEY (`album_id`) REFERENCES `photo_album` (`Album_ID`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4314 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

image_shout表 -

CREATE TABLE `image_shout` (
  `auto_id` int(11) NOT NULL AUTO_INCREMENT,
  `shout_id` int(11) DEFAULT NULL,
  `image_id` int(10) DEFAULT NULL,
  PRIMARY KEY (`auto_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1132 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

更新 -

将image_id列更改为无符号后的新错误是 -

 Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails
 (`void`.`#sql-36b_7285`, CONSTRAINT `fk_image` FOREIGN KEY (`image_id`) 
  REFERENCES `images` (`image_id`) ON DELETE SET NULL ON UPDATE CASCADE)

此致

Answer 1

问题如下。根据文档，必须索引外键。此外，外键应该引用另一个表的KEY。不只是一个专栏。如果您不想更改表格结构，请尝试使用auto_id作为约束。

Please see MySQL Documentation for the list of requirements of a Foreign Key constraint.

CREATE TABLE `image_shout` (
  `auto_id` int(11) NOT NULL AUTO_INCREMENT,
  `shout_id` int(11) DEFAULT NULL,
  `image_id` int(10) DEFAULT NULL,
  PRIMARY KEY (`auto_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1132 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

Answer 2

是因为表格图片中的image_id被定义为unsigned

`image_id` int(10) unsigned NOT NULL AUTO_INCREMENT,

并且在image_shout中

`image_id` int(10) DEFAULT NULL,

将两列更改为相同的数据类型，它应该可以正常工作。

mysql无法添加外键，原因不明

2 个答案: