(SELECT post_id FROM posts_articles
              WHERE MATCH(title) AGAINST('Knee+ Cartilage+ Repairing+ Market' IN BOOLEAN MODE)
              ORDER BY title ASC LIMIT 0, 5)
              UNION
              (SELECT post_id FROM posts_articles
              WHERE MATCH(tags) AGAINST('Knee+ Cartilage+ Repairing+ Market' IN BOOLEAN MODE)
              ORDER BY title ASC LIMIT 0, 5)