CODEWITHSUNDEEP
mysqlforeign-keysalter-table
Jerec TheSith
Jerec TheSith

Reputation: 1942

Foreign keys with mySQL

I have a table that references a reservation and a product, but I can't add any foreign key.

Here is the table :

CREATE TABLE IF NOT EXISTS `resa_product` (
  `id_reservation` int(10) NOT NULL,
  `id_business` int(10) NOT NULL,
  `id_category` int(10) NOT NULL,
  `id_product` int(10) NOT NULL,
  `quantity` int(11) NOT NULL,
  PRIMARY KEY (`id_reservation`,`id_business`,`id_category`,`id_product`),
  KEY `resa_prod_index` (`id_business`,`id_category`,`id_product`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

The product table :

CREATE TABLE IF NOT EXISTS `product` (
  `id_business` int(10) NOT NULL,
  `id_product` int(10) NOT NULL AUTO_INCREMENT,
  `id_category` int(10) NOT NULL,
  `nom` varchar(32) COLLATE utf8_unicode_ci NOT NULL,
 ...
  PRIMARY KEY (`id_product`,`id_category`,`id_business`),
  KEY `id_category` (`id_category`),
  KEY `id_business` (`id_business`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=5 ;

but when I try this, I get the errno 150 from mySQL :

ALTER TABLE `resa_product`
ADD FOREIGN KEY (`id_business`, `id_category`, `id_product`)
REFERENCES `product`(`id_business, `id_category`, `id_product`)
ON UPDATE CASCADE
ON DELETE RESTRICT;

I don't understand why I can't insert this composed key, although I added an index. Do someone has an idea ?

thanks for your help

Upvotes: 0

Views: 155

Answers (2)

gbn
gbn

Reputation: 432742

In the product table

  • data type and collation of the 3 columns must match
  • there must be a unique constraint or index on the 3 columns in the same order as the FK

Edit: after question update.

Change the foreign key to this to align column order to the PK of product

ALTER TABLE `resa_product`
ADD FOREIGN KEY (`id_product`, `id_category`, `id_business`)
REFERENCES `product`(`id_product, `id_category`, `id_business`)
ON UPDATE CASCADE
ON DELETE RESTRICT;

However, the 3 columns appear in different orders all over the show. I'd fix this to be consistent personally...

Upvotes: 1

GolezTrol
GolezTrol

Reputation: 116200

Most common reason for this problem is a slight difference between the columns in products and resa_product. The field types need to be exactly the same, so the size/precision and the sign (unsigned or not) all need to match.

Upvotes: 1

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