How to prev() a record

[Watson]

haw to prev() a record

  function prev_record() {
    if (!$query_id) {
      $query_id = $this->query_result;
    }
    if ($query_id) {
	  return prev($this->fetch_array());
    }	
  }
---------------------------------------


$sql = "SELECT * FROM bbs LIMIT 0,5";
$db->query($sql);

$rec = $db->prev_record();
echo $rec[note]."<br>";

I can't get any result.