instance method build_count_subquery

# File activerecord/lib/active_record/relation/calculations.rb, line 675
      def build_count_subquery(relation, column_name, distinct)
        if column_name == :all
          column_alias = Arel.star
          relation.select_values = [ Arel.sql(FinderMethods::ONE_AS_ONE) ] unless distinct
          relation.unscope!(:order)
        else
          column_alias = Arel.sql("count_column")
          relation.select_values = [ relation.aggregate_column(column_name).as(column_alias) ]
        end

        subquery_alias = Arel.sql("subquery_for_count", retryable: true)
        select_value = operation_over_aggregate_column(column_alias, "count", false)

        relation.build_subquery(subquery_alias, select_value)
      end