PHP/MySQL OnClick Update MySQL

需要在用户点击横幅广告时更新MySQL表中的hitcount字段。有随机广告显示脚本工作，但不能弄清楚如何更新表时，他们点击..假设将不得不传递ID到Ajax，但不知道如何接近它?代码如下:

include 'connection.php';
$query = "select * from ads where adtype = 'small' and status = 'yes' ORDER BY RAND() LIMIT 3";
$result = mysql_query($query) or die(mysql_error());
$num_results = mysql_num_rows($result);
if ($num_results !="0")
{
for($i=0;$i<$num_results;$i++)
{
    $row = mysql_fetch_array($result);
    $client = htmlspecialchars(stripslashes($row['client']));
    $link = htmlspecialchars(stripslashes($row['link']));
    $filename = htmlspecialchars(stripslashes($row['filename']));
    $id = $row['id'];
    echo "<tr>";
    echo "<td>";
    echo '<a href="';
    echo $link;
    echo '"><img src="thimg/';
    echo $filename;
    echo '" alt="';
    echo $client;
    echo '"></a>';
    echo "</td>";
    echo "</tr>";
}
}