Drop the backticks around integers. See the fiddle.
CREATE TABLE IF NOT EXISTS `PREFIX_quote` (
`id_quote` int(10) NOT NULL AUTO_INCREMENT,
`reference` varchar(9) DEFAULT NULL,
`id_shop_group` int(11) NOT NULL DEFAULT 1,
`id_shop` int(11) NOT NULL DEFAULT 1,
`id_lang` int(10) NOT NULL DEFAULT 1,
`id_customer` int(10) NOT NULL,
`total_discounts` decimal(17,2) NOT NULL DEFAULT 0.00,
`total_products` decimal(17,2) NOT NULL DEFAULT 0.00,
`total_product_wt` decimal(17,2) NOT NULL DEFAULT 0.00,
`total_shipping` decimal(17,2) NOT NULL DEFAULT 0.00,
`quote_number` int(10) NOT NULL DEFAULT 0,
`quote_date` datetime NOT NULL,
`valid` int(1) NOT NULL DEFAULT 1,
`id_employee` int(11) NOT NULL,
`date_add` datetime NOT NULL,
`date_upd` datetime NOT NULL,
PRIMARY KEY (`id_quote`),
KEY `id_customer` (`id_customer`),
KEY `id_employee` (`id_employee`));