# 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