_order_columns

# File activerecord/lib/active_record/relation/finder_methods.rb, line 634
      def _order_columns
        oc = []

        oc << implicit_order_column if implicit_order_column
        oc << query_constraints_list if query_constraints_list

        if primary_key && query_constraints_list.nil?
          oc << primary_key
        end

        oc.flatten.uniq.compact
      end