php无限归类

php无限分类
db设计：

CREATE TABLE IF NOT EXISTS `test` (
    `id` INT(1) NOT NULL AUTO_INCREMENT,
    `path` VARCHAR(255) NOT NULL,
    `name` VARCHAR(255) NOT NULL,
    PRIMARY KEY (`id`))ENGINE = MYISAM DEFAULT CHAR SET ='utf8';

INSERT INTO `test` VALUES
    ('', '0', '公司'),
    ('', '0-1', '部门一'),
    ('', '0-2', '部门二'),
    ('', '0-3', '部门三'),
    ('', '0-1-1', '小组一'),
    ('', '0-1-2', '小组二'),
    ('', '0-2-1', '小组三'),
    ('', '0-2-2', '小组四');

php代码实现：

<?php
$db = mysql_connect('localhost', 'root', 'zhw') or die('could not conenct to db');
mysql_query("SET charset 'utf8'");
mysql_select_db('test', $db);
$query = mysql_query("SELECT `id`, concat(`path`, '-', id) AS pwd, `name` FROM `test` ORDER BY `pwd`");
while ($row = mysql_fetch_array($query))
{
    $indent = str_repeat('    ', count(explode('-', $row['pwd'])) - 2);
    $option .= "<option value='{$row['id']}'>{$indent}{$row['name']}</option>";
}
echo "<select>{$option}</select>";