ajax get method - php

Question

UPDATE... this is the code I've implemented from the tutorial, within chrome dev tools in network i can see in header the variable is being sent and in preview i can see the drop down menu however it is not inserted into the loaded webpage
<script type="text/javascript">
$(document).ready(function() {
$('#selectEvidence').change(function(){
alert($(this).val());
});
});
function evidencesearch(str)
{
if (str=="")
{
document.getElementById("case").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.status==200)
{
document.getElementById("case").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","searchfunction.php?variable="+str,true);
xmlhttp.send();
}
</script>
<?php
$variable = $_GET['variable']; //used for second drop down menu
//echo "test test test $variable";
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = '';
$db = 'fid';
$conn = mysql_connect($dbhost,$dbuser,$dbpass);
if (!$conn)
die('Could not connect: ' . mysql_error());
mysql_select_db($db);
echo '<label class="input" for="case" type="input">Specify: </label><select id="case" name="case"><option=value"null"></option>'; //Insert to loaded page
$resource = mysql_query("SELECT $variable FROM `evidence`");
if($resource && mysql_num_rows($resource)) {
while ($row = mysql_fetch_assoc($resource)){
echo '<option value="'.$row[$variable].'">'.$row[$variable].'</option></select>';//Insert to loaded page
}
}
mysql_close($conn)
?>

Answer 1

I think your problem sticks within POST/GET functions; try to call them synchronously and paste please the w3schools tutorial's link you mentioned. Maybe I can help you then by writing more detailed answer.
Cheers.