public function get_sql_sort() {
        $columns = $this->get_sort_columns();
        if (count($columns) == 1 && isset($columns['timemodified']) && $columns['timemodified'] == SORT_DESC) {
            // Add the 'id' column when we are using the default sorting.
            $columns['id'] = SORT_DESC;
            return self::construct_order_by($columns);
        }
        return parent::get_sql_sort();
    }