php无限极分类

<?php$dsn = "mysql:host=127.0.0.1;port=3306;dbname=light-tips;charset=UTF8;";$username = 'root';$password = 'admin';$pdo = new PDO($dsn, $username, $password);$sql = 'SELECT * FROM `categories` ORDER BY `parentCategory`, `sortInd`';$result = $pdo->query($sql, PDO::FETCH_OBJ);$categories = [];foreach ($result as $category) {    $categories[$category->parentCategory][] = $category;}function showCategoryTree($categories, $n){    if (isset($categories[$n])) {        foreach ($categories[$n] as $category) {            echo str_repeat('-', $n) . $category->categoryName . PHP_EOL;            showCategoryTree($categories, $category->id);        }    }    return;}showCategoryTree($categories, 0);