public function rewind()
    {
        if ($this->_index == 0) {
            return;
        }

        if (!$this->_useBuffering) {
            $msg = 'You cannot rewind an un-buffered ResultSet. Use Query::bufferResults() to get a buffered ResultSet.';
            throw new Exception($msg);
        }

        $this->_index = 0;
    }