public function select_many_expr()
        {
            $columns = func_get_args();

            if (!empty($columns)) {
                $columns = $this->_nOnealiseSelectManyColumns($columns);

                foreach ($columns as $alias => $column) {
                    if (is_numeric($alias)) {
                        $alias = null;
                    }

                    $this->select_expr($column, $alias);
                }
            }

            return $this;
        }