无法添加外键约束

Question

I have created a database "webportal". and this is my "user" table script

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `firstName` varchar(255) DEFAULT NULL,
  `lastName` varchar(255) DEFAULT NULL,
  `dateRegistered` DATE DEFAULT NULL,
  `skypeID` int(11)  DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

and this one is "catalog" table script.

DROP TABLE IF EXISTS `catalog`;
create table catalog(
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `link`  VARCHAR(100) NOT NULL,
  `comment`  VARCHAR(100) NOT NULL,
  `inserDate` DATE DEFAULT NULL,
  `content` longblob NOT NULL,
  PRIMARY KEY (`id`),
  CONSTRAINT `fk_catalog` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

and when I try to execute the second script in the command line, I get this error...

ERROR 1215 (HY000): Cannot add foreign key constraint. What is wrong with this code?

Answer 1

It seems you are using a old version of MySQL, you can add a INDEX clause to foreign key field to fix the problem:

DROP TABLE IF EXISTS `catalog`;
create table `catalog`(
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `link`  VARCHAR(100) NOT NULL,
  `comment`  VARCHAR(100) NOT NULL,
  `inserDate` DATE DEFAULT NULL,
  `content` longblob NOT NULL,
  PRIMARY KEY (`id`),
  INDEX (`user_id`),
  CONSTRAINT `fk_catalog` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;