execute_simple_calculation

# File activerecord/lib/active_record/relation/calculations.rb, line 483
      def execute_simple_calculation(operation, column_name, distinct) # :nodoc:
        if build_count_subquery?(operation, column_name, distinct)
          # Shortcut when limit is zero.
          return 0 if limit_value == 0

          relation = self
          query_builder = build_count_subquery(spawn, column_name, distinct)
        else
          # PostgreSQL doesn't like ORDER BY when there are no GROUP BY
          relation = unscope(:order).distinct!(false)

          column = relation.aggregate_column(column_name)
          select_value = operation_over_aggregate_column(column, operation, distinct)
          select_value.distinct = true if operation == "sum" && distinct

          relation.select_values = [select_value]

          query_builder = relation.arel
        end

        query_result = if relation.where_clause.contradiction?
          if @async
            FutureResult.wrap(ActiveRecord::Result.empty)
          else
            ActiveRecord::Result.empty
          end
        else
          skip_query_cache_if_necessary do
            model.with_connection do |c|
              c.select_all(query_builder, "#{model.name} #{operation.capitalize}", async: @async)
            end
          end
        end

        query_result.then do |result|
          if operation != "count"
            type = column.try(:type_caster) ||
              lookup_cast_type_from_join_dependencies(column_name.to_s) || Type.default_value
            type = type.subtype if Enum::EnumType === type
          end

          type_cast_calculated_value(result.cast_values.first, operation, type)
        end
      end