PHP学习：PHP+mysql实现从数据库获取下拉树功能示例

<?php
include "config.php";
include "MySQL.php";
$db = new Mysql('test'); //几个简单的类,不用列出来大家也看得懂.就是实例化一个数据库连接而已.
function RootMenu ($PID,$n){
global $arr,$db;
$sql = "select * from menu where `PID` =$PID";
$result = $db->query($sql);
while ($i=$db->fetch_array($result)){
  $i["TITLE"] =str_repeat('--',$n).$i["TITLE"];
  $arr[] =$i;
  RootMenu($i["ID"],($n+4));
}
return $arr;
}
$arr = RootMenu(0,0);
?>
<select id="">
<option value="0" selected="selected">请选择部门</option>
<?php
for ($i=0;$i<count($arr);$i++) {
?>
<option value="<?php echo $arr[$i]["ID"] ?>"><?php echo $arr[$i]["TITLE"] ?></option>
<?php }?>
</select>