PHP利用递归函数实现无限级分类的方法

CREATE TABLE IF NOT EXISTS `category` (
 `id` int(5) NOT NULL AUTO_INCREMENT COMMENT '唯一自增id',
 `pid` int(5) NOT NULL DEFAULT '0' COMMENT '父id',
 `sort` int(2) NOT NULL DEFAULT '0' COMMENT '排序数字',
 `name` varchar(30) DEFAULT NULL COMMENT '名称',
 PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='无限极分类表' AUTO_INCREMENT=1 ;

INSERT INTO `category` (`id`, `pid`, `sort`, `name`) VALUES
(1, 0, 1, 'php'),
(2, 0, 2, '数据库'),
(3, 0, 3, 'javascript'),
(4, 1, 1, '框架模板'),
(5, 1, 2, '函数总结'),
(6, 2, 1, 'mysql'),
(7, 4, 1, '框架'),
(8, 4, 2, '模板'),
(9, 8, 1, 'smarty'),
(10, 7, 2, 'thinkphp'),
(11, 10, 1, 'thinkphp技巧'),
(12, 10, 2, 'thinkphp模板'),
(13, 12, 3, '模板知识总结'),
(14, 12, 2, '模板视频教程'),
(15, 11, 1, 'model技巧');

function tree(&$list,$pid=0,$level=0,$html='--'){
  static $tree=array();
  foreach($list as $v){
    if($v['pid']==$pid){
      $v['level']=$level;
      $v['html']=str_repeat($html,$level);
      $tree[]=$v;
      tree($list,$v['id'],$level+1,$html);
    } 
  }
  return $tree;
}