Ajax dropdown php table sorting

I have a page which has a dropdown box. On selection a value is sent to a php script (Ajax), based on the value a html table is created and sent back to the responseText. The table is output to the HTML page. I want the table to have sortable columns, so I have used jQuery datatables for this, but it is not working.

I have cut and pasted the exact table into the html and ran the page, and then sorting works.

Please can anyone help / advise to fix this?

Note the table output from the php is outputted inbetween:

<a div id="txtHint"> <table id="example"> <div>

Here is the rest of the code on the HTML page:

<script type="text/javascript" src="/js/jquery-1.5.1.js"></script>
<script type="text/javascript" src="/js/jquery.dataTables.js"></script>
<script type="text/javascript" charset="utf-8"> 
$(document).ready(function() {
    $('table#example').dataTable( {
        "sPaginationType": "full_numbers"
    } );
} );
</script> 

<script type="text/javascript">
function selMetal(str,str2){
    if (str==""){
    document.getElementById("txtHint").innerHTML="";
        return;
    } 
    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.statu开发者_如何学编程s==200){
            document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
        }
    }
    xmlhttp.open("GET","sql.php?m="+str+"&s="+str2,true);
    xmlhttp.send();
}
</script>

Where is #example defined? Are you recreating the html for the entire table in ajax?

If so, you are probably overwriting the #example dom element that jquery dataTable already manipulated. Try re-instantiating the data table after you set the table html, such as:

xmlhttp.onreadystatechange=function(){ 
       if (xmlhttp.readyState==4 && xmlhttp.status==200){
            document.getElementById("txtHint").innerHTML=xmlhttp.responseText; 
           $('table#example').dataTable().fnDestroy(); // might need to destroy the old one first - not sure
           $('table#example').dataTable( { "sPaginationType": "full_numbers" } );
       } 
  }