Foreign key constraint is incorrectly formed (MySQL) [closed]

Question

Closed. This question is off-topic. It is not currently accepting answers.

---

Want to improve this question? Update the question so it's on-topic for Database Administrators Stack Exchange.

Closed 5 months ago.

Improve this question

So, I have these two tables

CREATE TABLE IF NOT EXISTS `inart_ps_categories` (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `inart_ps_category_id` int(11) UNSIGNED NOT NULL,
  `parent_id` int(11) UNSIGNED DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `path` varchar(255) DEFAULT NULL,
  `num_children` int(11) DEFAULT '0',
  `flag` tinyint(1) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE utf8_general_ci;

CREATE TABLE IF NOT EXISTS `inart_ps_category_associations` (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `inart_ps_category_id` int(11) UNSIGNED NOT NULL,
  `categoryid` int(11) NOT NULL,
  PRIMARY KEY (`id`),
    FOREIGN KEY (categoryid) REFERENCES `categories` (categoryid) ON DELETE CASCADE,
    FOREIGN KEY (inart_ps_category_id) REFERENCES `inart_ps_categories` (inart_ps_category_id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE utf8_general_ci;

It outputs "Foreign key constraint is incorrectly formed" for no reason. The first Foreign key is correct and if I erase the second one, the query is executed. Can you see something wrong here?

Answer 1

Without seeing your categories table, your only problem is that the referenced columns like inart_ps_category_id need an index, which you can achieve by using KEY(inart_ps_category_id):

CREATE TABLE IF NOT EXISTS `inart_ps_categories` (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `inart_ps_category_id` int(11) UNSIGNED NOT NULL,
  `parent_id` int(11) UNSIGNED DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `path` varchar(255) DEFAULT NULL,
  `num_children` int(11) DEFAULT '0',
  `flag` tinyint(1) NOT NULL,
  PRIMARY KEY (`id`),
  KEY(`inart_ps_category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE utf8_general_ci;

CREATE TABLE IF NOT EXISTS `inart_ps_category_associations` (
  `id` int(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `inart_ps_category_id` int(11) UNSIGNED NOT NULL,
  `categoryid` int(11) NOT NULL,
  PRIMARY KEY (`id`),
    FOREIGN KEY (categoryid) REFERENCES `categories` (categoryid) ON DELETE CASCADE,
    FOREIGN KEY (inart_ps_category_id) REFERENCES `inart_ps_categories` (inart_ps_category_id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE utf8_general_ci;

Answer 2

A Foreign Key should only reference the Primary Key of another table.

The one causing you difficulties does not.

CREATE TABLE inart_ps_categories 
( id int(11) UNSIGNED NOT NULL AUTO_INCREMENT
, inart_ps_category_id int(11) UNSIGNED NOT NULL
. . . 
, PRIMARY KEY ( id )                                           <-- Primary Key 
)

CREATE TABLE inart_ps_category_associations 
( id int(11) UNSIGNED NOT NULL AUTO_INCREMENT
, inart_ps_category_id int(11) UNSIGNED NOT NULL
. . . 
, PRIMARY KEY ( id )
. . . 
  FOREIGN KEY ( inart_ps_category_id ) 
    REFERENCES inart_ps_categories ( inart_ps_category_id )    <-- NOT Primary Key 
)