php 读取三级分类

<?php
// 连接数据库
$host = 'localhost';
$dbname = 'your_database';
$user = 'your_username';
$pass = 'your_password';

try {
    $pdo = new PDO("mysql:host=$host;dbname=$dbname;charset=utf8", $user, $pass);
} catch (PDOException $e) {
    die("数据库连接失败: " . $e->getMessage());
}

// 查询三级分类
$query = "
SELECT c1.name AS level1, c2.name AS level2, c3.name AS level3
FROM categories c1
LEFT JOIN categories c2 ON c2.parent_id = c1.id
LEFT JOIN categories c3 ON c3.parent_id = c2.id
WHERE c1.parent_id IS NULL
";

try {
    $stmt = $pdo->query($query);
    $categories = $stmt->fetchAll(PDO::FETCH_ASSOC);
} catch (PDOException $e) {
    die("查询失败: " . $e->getMessage());
}

// 显示分类
echo "<ul>";
foreach ($categories as $category) {
    echo "<li>{$category['level1']} > {$category['level2']} > {$category['level3']}</li>";
}
echo "</ul>";
?>