SELECT a.id, a.title, 
       c.name,
       i.file, i.alt

  FROM article     AS a
  JOIN category    AS c   ON a.category_id = c.id
  LEFT JOIN image  AS i   ON a.image_id    = i.id

 WHERE a.category_id = 3 
   AND a.published   = 1
 ORDER BY a.id DESC;