named_scope :sort, lambda { |*args| { :conditions => "id IN (
                                                        SELECT item_id
                                                        FROM taggings
                                                        WHERE tag_id IN (#{args.join(',')})
                                                        GROUP BY item_id
                                                        HAVING COUNT(item_id)=#{args.size}
                                                        )"
                                                        } }