RAND and GROUP BY

this mysql command work fine, but RAND not working. Showing me only one last product every refresh page.

Sorry for my English.

$offers = mysql_query("SELECT * FROM firmy INNER JOIN offers ON firmy.id=offers.id_comp " . $WHERE_OFFERS . " GROUP BY firmy.id, offers.id_comp ORDER BY RAND () LIMIT 0,3") or die(mysql_error());