CREATE TABLE `companies` (
	`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
	`name` varchar(255) NOT NULL,
	`blocked` tinyint(1) NOT NULL DEFAULT '0',
	PRIMARY KEY (`id`)
);

CREATE TABLE `products` (
	`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
	`company` int(11) unsigned NOT NULL,
	`name` varchar(255) COLLATE utf8_bin NOT NULL,
	`price` varchar(15) CHARACTER SET utf8 NOT NULL DEFAULT '',
	PRIMARY KEY (`id`),
	KEY `company` (`company`)
);

SELECT * FROM (
	SELECT P.name AS product_name, P.price AS product_price, C.id AS company_id, C.name AS company_name
	FROM companies C
	INNER JOIN products P ON C.id = P.company
	WHERE C.id IN (1,2,3,...)
	ORDER BY RAND()
) AS random_products
GROUP BY company_id
LIMIT 10

SELECT product_id, product_name, product_price, company_id, company_name
FROM (
   SELECT *, @num := IF(@company = company_id, @num + 1, 1) AS row_number, @company := company_id AS dummy
   FROM (
       SELECT P.id AS product_id, P.name AS product_name, P.price AS product_price, P.company AS company_id, C.name AS company_name
       FROM products P
       LEFT JOIN companies C ON C.id = P.company
       ORDER BY P.company, RAND()
   ) AS t1
) AS t2
WHERE t2.row_number <= /*N*/
ORDER BY RAND()
LIMIT /*M*/

SET @num := 0, @company := 0