named_scope :random, lambda { |*args| { :joins => "JOIN (SELECT id
                                                              FROM #{table_name}
                                                              ORDER BY RAND()
                                                              LIMIT #{(limit = args.first.to_i) > 0 ? limit : 1}
                                                             ) AS random_ids
                                                        ON #{table_name}.id = random_ids.id"}}