Making a Like/Dislike AJAX script - Not working
<div id="voting">
<form>
  <input name="vote" type='button' onclick="getVote(<?php echo $image['filename'];?>)" value='Like' />
    </form>
</div>

<script type="text/javascript">
function getVote(filename)
{
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("voting").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","voting.php"+filename,true);
xmlhttp.send();
}
</script>

<?php
//Database Information
$dbhost = "";
$dbname = "";
$dbuser = "";
$dbpass = "";

//Connect to database
mysql_connect ( $dbhost, $dbuser, $dbpass)or die("Could not connect: ".mysql_error());
mysql_select_db($dbname) or die(mysql_error());

$filename = $_GET['filename'];

$query = "UPDATE images SET rating = rating+1 WHERE filename = '$filename'";

mysql_query($query) or die(mysql_error());
mysql_close();

?>

xmlhttp.open("GET","voting.php?filename="+filename,true);

$filename = isset($_GET['filename']) ? mysql_real_escape_string($_GET['filename']) : null ;

if (is_null($filename)) {
    exit;
}