<form name="form1">
<select name="users" onchange="showUser(this.value)">
<option value="">Selecteer</option>
<option value="100">Peter</option>
<option value="101">Klaas</option>
<option value="102">Jan</option>
<option value="103">Piet</option>
</select>
</form>
function showUser(str)
{
if (str=="")
{
document.getElementById("input1").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("input1").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","get_users.php?q="+str,true);
xmlhttp.send();
}
<<get_users.php>>
<?php
include("Includes/functions.php");
include("Includes/connection.php");
$q=$_GET["q"];
$query= mysql_query("
SELECT
*
FROM
test_tabel
WHERE
id = '".$q."'"
,$connection);
$row = mysql_fetch_assoc($query);
echo $row['achternaam'];
mysql_close($connection);
?>