Retrieving multiple data via ajax

[springb5]

Hey. Anybody with Ajax & PHP knowledge that can help me?

I have a booking form which I would like to check with the database before we submit.

When the customer clicks on a product & selects a date, I want to know if it's available or not.

Here's what I have so far... I've never used ajax before, so there's no wonder it doesn't work.

Product fields ID's are: product, product2, product3. Date field ID is startdate.

AJAX:

<script language = "javascript" type = "text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){
var ajaxRequest; // The variable that makes Ajax possible!

try {
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
}catch (e) {
// Internet Explorer Browsers
try {
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
}catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
}catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}

// Create a function that will receive data
// sent from the server and will update
// div section in the same page.
ajaxRequest.onreadystatechange = function(){
if(ajaxRequest.readyState == 4){
var ajaxDisplay = document.getElementById('ajaxDiv');
ajaxDisplay.innerHTML = ajaxRequest.responseText;
}
}

// Now get the value from user and pass it to
// server script.
var p1 = document.getElementById('product').value;
var p2 = document.getElementById('product2').value;
var p3 = document.getElementById('product3').value;
var sd = document.getElementById('startdate').value;
var queryString = "?sd=" + sd ;

queryString += "&p1=" + p1 + "&p2=" + p2 + "&p3=" + p3;
ajaxRequest.open("GET", "getuser.php" + queryString, true);
ajaxRequest.send(null);
}
//-->
</script>


PHP: (getuser.php)
<?php
include 'connect.php';
$q = intval($_GET['sd']);
$p1 = intval($_GET['p1']);
$p2 = intval($_GET['p2']);
$p3 = intval($_GET['p3']);
$sqlavailable="SELECT * FROM bookings WHERE startdate = '".$q."'";
$result = mysqli_query($link,$sqlavailable);
while($row = mysqli_fetch_array($result)) {
IF (($row[product] == $p1) OR ($row[product2] == $p1) OR ($row[product3] == $p1)) {
echo '".$p1." unavailable';
} else {
echo '".$p1." available';
}
IF (($row[product] == $p2) OR ($row[product2] == $p2) OR ($row[product3] == $p2)) {
echo '".$p2." unavailable';

} else {
echo '".$p2." available';
}​

IF (($row[product] == $p3) OR ($row[product2] == $p3) OR ($row[product3] == $p3)) {
echo '".$p3." unavailable';

} else {
echo '".$p3." available';
}​

}
mysqli_close($link);
?>

Would really appreciate any input. Thanks in advance.