(SELECT * FROM `news` WHERE `categoria` LIKE '9' ORDER BY `id` DESC LIMIT 10)
union
(SELECT * FROM `news` WHERE `categoria` LIKE '10' ORDER BY `id` DESC LIMIT 10)
union
(SELECT * FROM `news` WHERE `categoria` LIKE '11' ORDER BY `id` DESC LIMIT 10)


sicuro ti serva il like anzichè l'uguale per la categoria?