final protected function order_by($column, $order = 'ASC'){
        $order = 'DESC' === strtoupper($order) ? 'DESC' : 'ASC';
        $this->_order_by[] = sprintf('%s %s', $this->escape_column_name($column), $order);
        return $this;
    }
final protected function order_by($column, $order = 'ASC'){
        $order = 'DESC' === strtoupper($order) ? 'DESC' : 'ASC';
        $this->_order_by[] = sprintf('%s %s', $this->escape_column_name($column), $order);
        return $this;
    }
final protected function order_by ( $ column , $ order = 'ASC' ) { $ order = 'DESC' === strtoupper ( $ order ) ? 'DESC' : 'ASC' ; $ this -> _order_by [ ] = sprintf ( '%s %s' , $ this -> escape_column_name ( $ column ) , $ order ) ; return $ this ; }
Add order by

@param string $column
@param string $order
@return $this
Add order by