1-3 /ajax.php

<?php
include "../../mainfile.php";

$county=$_POST['county'];

$sql = "select city from `" . $xoopsDB->prefix("phone_book") . "` where county='{$county}' group by city order by zip";
$result = $xoopsDB->query($sql) or redirect_header($_SERVER['PHP_SELF'], 3, mysql_error());
while (list($city) = $xoopsDB->fetchRow($result)) {
    echo "<option vlaue='{$city}'>{$city}</option>";
}