(SELECT post_id FROM posts_articles
              WHERE MATCH(title) AGAINST('+ISO +9001 +Implementation +in +Portugal' IN BOOLEAN MODE)
              ORDER BY title ASC LIMIT 0, 5)
              UNION
              (SELECT post_id FROM posts_articles
              WHERE MATCH(tags) AGAINST('+ISO +9001 +Implementation +in +Portugal' IN BOOLEAN MODE)
              ORDER BY title ASC LIMIT 0, 5)