依赖下拉列表自动选择值和加载数据

Question

您好我有2个下拉列表（客户端和产品）和1个内容数据。产品下拉列表取决于客户下拉列表中的选择（我已经这样做了）。问题是我想根据产品下拉列表中的选择自动加载内容数据。

这是我的代码：

float dataRX= (float)TrafficStats.GetUidRxBytes(Android.OS.Process.MyUid())/(float)(1024*1024);
float dataTX= (float)TrafficStats.GetUidTxBytes(Android.OS.Process.MyUid())/(float)(1024*1024);

filter_client.php：

<script>
    function filterClient(str) {
            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("ProductOpt").innerHTML = xmlhttp.responseText;
                }
            }
            xmlhttp.open("GET","filter_client.php?f=client&q="+str,true);
            xmlhttp.send();
        }
    function filterProduct(str) {
            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("content").innerHTML = xmlhttp.responseText;
                }
            }
            xmlhttp.open("GET","filter_product.php?f=product&k="+str,true);
            xmlhttp.send();
        }
</script>
<table border='0' style='float: right'>
    <tr>
        <td>
            <form>
                <select name='ClientFilter' onchange="filterClient(this.value);">
                    <option value='0' style="text-align: center">--Filter by Client--</option>
                    <?php
                    $clientDL = mysql_query("SELECT * FROM `Client`");
                    while($client=mysql_fetch_array($clientDL))
                        echo  "<option value='".$client['ClientID']."'>".$client['ClientName']."</option>";
                    ?>
                </select>
            </form>
        </td>
        <td>
            <form>
                <select name='ProductFilter' id="ProductOpt" onchange="filterProduct(this.value);">
                    <option value='' style="text-align: center">--Filter by Product--</option>
                </select>
            </form>
        </td>

    </tr>
</table>

<div id="content"></div>

filter_product.php：

<?php
if (file_exists("../../../../wp-load.php")) {
    require_once("../../../../wp-load.php");
}
$k = $_GET['k'];
global $dbhandle;//Database connection
if($q!=0) {
    if (isset($_GET['f']) && $_GET['f'] == 'client') {
        $productDL = mysql_query("SELECT * FROM `Product` where ProductID = " . $k);
        while ($product = mysql_fetch_array($productDL))
            echo "<option value='" . $product['ProductID'] . "'>" . $product['ProductName'] . "</option>";
    }
}
?>