class表结构：

CREATE TABLE IF NOT EXISTS `class` ( 
  `id` mediumint(6) NOT NULL AUTO_INCREMENT, 
  `title` varchar(30) NOT NULL, 
  `pid` mediumint(6) NOT NULL DEFAULT '0', 
  PRIMARY KEY (`id`) 
) ENGINE=MyISAM  DEFAULT CHARSET=utf8; 


<?php
$host="localhost:3306"; //数据库服务器名称 
$user="111"; //用户名 
$pwd="111"; //密码 
$conn=mysql_connect($host,$user,$pwd); 

mysql_query("set names 'utf8'",$conn); 

if ($conn==FALSE) 
{ 
	echo "<center>服务器连接失败！<br>请刷新后重试。</center>"; 
	return true; 
} 
	
$databasename="aaa";//数据库名称 

do 
{ 
	$con=mysql_select_db($databasename,$conn); 
}
while(!$conn); 

if ($conn==FALSE)
{ 
	echo "<center>打开数据库失败！<br>请刷新后重试。</center>"; 
	return true; 
} 

//连接数据库
?>


<?
function get_str($id = 0) { 
    global $str; 
    $sql = "select id,title from class where pid= $id";  
    $result = mysql_query($sql);//查询pid的子类的分类 
    if($result && mysql_affected_rows()){//如果有子类 
        $str .= '<ul>'; 
        while ($row = mysql_fetch_array($result)) { //循环记录集 
            $str .= "<li>" . $row['id'] . "--" . $row['title'] . "</li>"; //构建字符串 
            get_str($row['id']); //调用get_str()，将记录集中的id参数传入函数中，继续查询下级 
        } 
        $str .= '</ul>'; 
    } 
    return $str; 
} 
//函数
?>


<?
echo get_str(0);
//调用
?>



-- phpMyAdmin SQL Dump
-- version 4.4.11
-- http://www.phpmyadmin.net
--
-- Host: localhost:3306
-- Generation Time: 2017-09-11 11:18:03
-- 服务器版本： 5.5.40
-- PHP Version: 5.3.29

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;

--
-- Database: `bixing`
--

-- --------------------------------------------------------

--
-- 表的结构 `class`
--

CREATE TABLE IF NOT EXISTS `class` (
  `id` mediumint(6) NOT NULL,
  `title` varchar(30) NOT NULL,
  `pid` mediumint(6) NOT NULL DEFAULT '0'
) ENGINE=MyISAM AUTO_INCREMENT=12 DEFAULT CHARSET=utf8;

--
-- 转存表中的数据 `class`
--

INSERT INTO `class` (`id`, `title`, `pid`) VALUES
(1, '品牌女装', 0),
(2, '精品男装', 0),
(3, '精致内衣', 0),
(4, '服饰配件', 0),
(5, '连衣裙', 1),
(6, '半身裙', 1),
(7, '旗袍', 1),
(8, '针织衫', 1),
(9, '皮衣', 2),
(10, '夹克', 2),
(11, 'aa', 10);

--
-- Indexes for dumped tables
--

--
-- Indexes for table `class`
--
ALTER TABLE `class`
  ADD PRIMARY KEY (`id`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `class`
--
ALTER TABLE `class`
  MODIFY `id` mediumint(6) NOT NULL AUTO_INCREMENT,AUTO_INCREMENT=12;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;