module ActiveRecord::Calculations

def perform_calculation(operation, column_name)
  operation = operation.to_s.downcase
  # If #count is used with #distinct (i.e. `relation.distinct.count`) it is
  # considered distinct.
  distinct = distinct_value
  if operation == "count"
    column_name ||= select_for_count
    if column_name == :all
      if !distinct
        distinct = distinct_select?(select_for_count) if group_values.empty?
      elsif group_values.any? || select_values.empty? && order_values.empty?
        column_name = primary_key
      end
    elsif distinct_select?(column_name)
      distinct = nil
    end
  end
  if group_values.any?
    execute_grouped_calculation(operation, column_name, distinct)
  else
    execute_simple_calculation(operation, column_name, distinct)
  end
end