    # File lib/active_record/calculations.rb, line 134
          def calculate(operation, column_name, options = {})
            validate_calculation_options(operation, options)
            column_name     = options[:select] if options[:select]
            column_name     = '*' if column_name == :all
            column          = column_for column_name
            aggregate       = select_aggregate(operation, column_name, options)
            aggregate_alias = column_alias_for(operation, column_name)
            if options[:group]
              execute_grouped_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
            else
              execute_simple_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
            end
          end