Question

With the following tables

CREATE TABLE `Play` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) DEFAULT NULL,
  `room_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `IDX_FEBB7184A76ED395` (`user_id`),
  KEY `IDX_FEBB718454177093` (`room_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

CREATE TABLE `User` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) NOT NULL,
  `nickname` varchar(255) NOT NULL,
  `email` varchar(255) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UNIQ_2DA17977F85E0677` (`username`),
  UNIQUE KEY `UNIQ_2DA17977A188FE64` (`nickname`),
  UNIQUE KEY `UNIQ_2DA17977E7927C74` (`email`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

INSERT INTO `User` VALUES(1, 'user', 'nickname', '[e-mail]');

CREATE TABLE `Room` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

INSERT INTO `Room` VALUES(1);

ALTER TABLE `Play`
  ADD CONSTRAINT `play_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `User` (`id`),
  ADD CONSTRAINT `play_ibfk_2` FOREIGN KEY (`room_id`) REFERENCES `Room` (`id`);

And trying to run the following statement

INSERT INTO `Play` (`id` ,`user_id` ,`room_id`) VALUES (NULL ,  '1',  '1')

I get an error

#1452 - Cannot add or update a child row: a foreign key constraint fails
(`play`, CONSTRAINT `play_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `User` (`id`))

Both data sets, #1 of User and #1 of Room exist in the databse. How can this fail? I am quite familiar with SQL, but I have no idea what the error is in this case…

Answer 1

Fixed it. It was an issue that only comes up when using MySQL 5.5.9, InnoDB and Mac OS X 10.6

See: MySQL Bug #60309

I changed the .conf of MySQL to add this line:

[mysqld]
lower_case_table_names=1

And it works now. Thanks for your help anyway.