php递归实现无限分类

<?php
/**
 * php递归实现的无限分类
 *
 *
 */
header("Content-type: text/html; charset=utf-8");
error_reporting(E_ALL);

//mysql_connect ...

$link = mysql_connect('localhost','root','');

mysql_select_db('test');
mysql_query('set names utf8');

global $i,$parentid;

function tree($parentid) {

 $i = 0;
 $result = mysql_query('Select * FROM `test_fenlei` Where `parent_id` = '.$parentid) OR die("Invalid query: " . mysql_error());
 
 while($res = mysql_fetch_array($result))
 {
  echo $i++;
  echo str_repeat('　',$res['level']).$res['name'].'<br />';
  tree($res['id']);

 }
 
}

if(($parentid + 0) < 1){

 $parentid = 0;

}

tree(0);

得到结果