Question

I got three tables, a parent one (called profiles) and two tables one can consider a child (values and url). This is just a test to play around so don’t mind missing SQL injection security.

CREATE TABLE `profiles` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
 `profile` int(10) unsigned NOT NULL,
 `url_hash` varchar(32) NOT NULL,
 PRIMARY KEY (`id`,`profile`,`url_hash`),
 UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=latin1


CREATE TABLE `urls` (
 `id` int(10) unsigned NOT NULL,
 `url` text NOT NULL,
 `title` text,
 PRIMARY KEY (`id`),
 CONSTRAINT `urls_ibfk_1` FOREIGN KEY (`id`) REFERENCES `profiles` (`id`) 
ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1


CREATE TABLE `values` (
 `id` int(10) unsigned NOT NULL,
 `seller` text NOT NULL,
 `seller_language` text,
 `quality` tinyint(3) unsigned NOT NULL,
 `note` text,
 `price` int(10) unsigned NOT NULL,
 `count` tinyint(3) unsigned NOT NULL,
 PRIMARY KEY (`id`),
 CONSTRAINT `values_mtg_ibfk_1` FOREIGN KEY (`id`) REFERENCES `profiles` (`id`) 
ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1

I’m executing the following three queries as transaction (surrounding autocommit(false), commit() & rollback() omitted):

$db->query('INSERT INTO profiles(id, profile, url_hash) 
VALUES (null, ' . $profile . ', "' . md5($url) . '")')
or throwException(...);

$db->query('INSERT INTO urls(id, url, title) 
VALUES (' . mysqli_insert_id($db) . ', "' . $url . '", "' . $c->data('title') . '")')
 or throwException(...);

$db->query('INSERT INTO values(id, seller, seller_language, quality, 
note, price, count) 
VALUES (' . mysqli_insert_id($db) . ', "'. $seller .'", "'. $seller_lang .'", 
'. $qual .', "'. $notice .'", '. $price .', '. $ount .')') 
or throwException(..);

Resulting in

exception 'Exception' with message 'Query failed (table: values): 
(1452) Cannot add or update a child row: a foreign key constraint fails
(`crawler`.`values`, CONSTRAINT `values_ibfk_1` FOREIGN KEY (`id`) REFERENCES
`profiles` (`id`) ON DELETE CASCADE ON UPDATE CASCADE)'

and I just don’t get why. It is stating the corresponding id in the parent table is missing. If that’s the case why does the second query work since its table urls got the very same foreign key relationship to table profiles like table values?

Edit: there is a huge flaw in my database design, regarding the FK in values which can’t be unique. Gonna think about it tomorrow. 🙂

Answer 1

The error resulted from my flawed database design (what I never thought of).
In values id was unique while my script tried to INSERT multiple values with the same id.