possible_aggregation?

# File activerecord/lib/active_record/relation/calculations.rb, line 469
      def possible_aggregation?(column_names)
        column_names.all? do |column_name|
          if column_name.is_a?(String)
            column_name.include?("(")
          else
            Arel.arel_node?(column_name)
          end
        end
      end