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    <p>Foreign keys must point at a column of an other table (which has to be the same (ex.: INT(11) - INT(11)). When your tables are created, you can add a foreign key by using</p> <pre><code>ALTER TABLE mytable ADD FOREIGN KEY (myfkey) REFERENCES myothertable(parentkey) </code></pre> <p>Now if we apply it to your structure:</p> <pre><code>DROP TABLE items; DROP TABLE brands; DROP TABLE products; CREATE TABLE IF NOT EXISTS `brands` ( `brandId` int(11) NOT NULL AUTO_INCREMENT, `brandName` varchar(30) NOT NULL, `brandLogo` varchar(100) NOT NULL, `brandDescription` text NOT NULL, PRIMARY KEY (`brandId`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ; INSERT INTO `brands` (`brandId`, `brandName`, `brandLogo`, `brandDescription`) VALUES (1, 'Samsung', '', 'Manufacturer of ...'), (2, 'Apple', '', 'American high-tech company ...'); CREATE TABLE IF NOT EXISTS `items` ( `itemId` int(11) NOT NULL AUTO_INCREMENT, `generalProductId` int(11) NOT NULL, `itemPurchasedPrice` double NOT NULL, `itemDateAdded` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, `itemDescription` text, `itemBrand` int(11) NOT NULL, `itemBoughtFromPlace` int(11) NOT NULL, `itemBoughtFromUser` int(11) NOT NULL, `itemConditionNew` tinyint(1) NOT NULL DEFAULT '1', `itemBeingSold` tinyint(1) NOT NULL DEFAULT '1', `itemSellPrice` double DEFAULT NULL, PRIMARY KEY (`itemId`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ; CREATE TABLE IF NOT EXISTS `products` ( `productId` int(11) NOT NULL AUTO_INCREMENT, `productName` varchar(200) NOT NULL, `productTimeAdded` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, `productDescription` text, `productBrand` int(11) NOT NULL, `productFirstAddedFrom` int(11) NOT NULL, `productAvatar` varchar(100) DEFAULT NULL, PRIMARY KEY (`productId`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=5 ; INSERT INTO `products` (`productId`, `productName`, `productTimeAdded`, `productDescription`, `productBrand`, `productFirstAddedFrom`, `productAvatar`) VALUES (3, 'Samsung Galaxy SII', '2013-10-26 07:46:08', 'The Samsung Galaxy S II is a .....', 1, 1, NULL), (4, 'iPhone 5', '2013-10-26 07:46:08', 'The iPhone 5 is a ....', 1, 2, NULL); ALTER TABLE items ADD FOREIGN KEY(generalProductId) REFERENCES products(productId) ON DELETE CASCADE ON UPDATE CASCADE; ALTER TABLE products ADD FOREIGN KEY(productBrand) REFERENCES brands(brandId) ON DELETE CASCADE ON UPDATE CASCADE; ALTER TABLE items ADD FOREIGN KEY(itemBrand) REFERENCES product(productBrand) ON DELETE CASCADE ON UPDATE CASCADE; </code></pre>
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    1. POThe way foreign keys work when there are 3 tables dependent on each other
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    1. USGrigory Kornilov
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    1. COI updated my question
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    2. COUpdated the answer)
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    3. COif I try to run the first sql, it says I have a syntax error. If I try to run the second longer one, it wont allow me, because "#1217 - Cannot delete or update a parent row: a foreign key constraint fails "
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