Question

首先，我已经阅读了有关此类错误类型的所有StackOverflow问题，我无法理解为什么会出现此错误。我有一个meetings表：

CREATE TABLE `meetings` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `description` text,
  `city` varchar(255) DEFAULT NULL,
  `start_time` datetime DEFAULT NULL,
  `end_time` datetime DEFAULT NULL,
  `owner` varchar(128) NOT NULL,
  `is_private` tinyint(1) DEFAULT NULL,
  `priority` int(11) DEFAULT NULL,
  `accepted_count` int(11) DEFAULT NULL,
  `creation_time` datetime DEFAULT CURRENT_TIMESTAMP,
  `main_pic` text,
  PRIMARY KEY (`id`),
  KEY `user_id_idx` (`owner`),
  KEY `city_fk_idx` (`city`),
  KEY `weight_idx` (`priority`),
  CONSTRAINT `city_fk` FOREIGN KEY (`city`) REFERENCES `cities` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `user_id` FOREIGN KEY (`owner`) REFERENCES `users` (`Id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `weight` FOREIGN KEY (`priority`) REFERENCES `priorities` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8;

我还有meeting_pictures表

CREATE TABLE `meeting_pictures` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `path` text NOT NULL,
  `meeting_id` int(11) NOT NULL,
  `user_id` varchar(128) NOT NULL,
  PRIMARY KEY (`id`,`meeting_id`),
  KEY `user_id_idx` (`user_id`),
  CONSTRAINT `user_id_fkk` FOREIGN KEY (`user_id`) REFERENCES `users` (`Id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

这就是我尝试添加新FK的方式：

ALTER TABLE `tts`.`meetings` 
ADD CONSTRAINT `meeting_pic_fk1`
  FOREIGN KEY (`id`)
  REFERENCES `tts`.`meeting_pictures` (`meeting_id`)
  ON DELETE NO ACTION
  ON UPDATE NO ACTION;

每次我都有：“ERROR 1215：无法添加外键约束”。为什么会这样？两列的类型相同。我怎样才能添加这样的FK？

由于

Answer 1

meeting_pictures上的主键由两部分组成：meeting_id和id。如果我不得不猜测，你打算让外键约束转向另一个方向：

ALTER TABLE tts.meeting_pictures 
    ADD CONSTRAINT meeting_pic_fk1
      FOREIGN KEY (meeting_id)
      REFERENCES tts.meetings (id)
      ON DELETE NO ACTION
      ON UPDATE NO ACTION;

至少，tts.meeting_picures(meeting_id)引用tts.meetings(id)对我有意义。

错误1215：无法添加外键约束。字段具有相同的类型

1 个答案: