php mysql树状分类

CREATE TABLE categories (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    parent_id INT DEFAULT NULL,
    FOREIGN KEY (parent_id) REFERENCES categories(id)
);

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 插入示例数据
$sql = "INSERT INTO categories (name, parent_id) VALUES
('电子产品', NULL),
('手机', 1),
('苹果手机', 2),
('安卓手机', 2),
('食品', NULL),
('水果', 5),
('苹果', 6);";

if ($conn->query($sql) === TRUE) {
    echo "数据插入成功";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

// 查询树状分类
function getTree($conn, $parentId = NULL) {
    $sql = "SELECT * FROM categories WHERE parent_id = ?";
    $stmt = $conn->prepare($sql);
    $stmt->bind_param("i", $parentId);
    $stmt->execute();
    $result = $stmt->get_result();

    $tree = [];
    while ($row = $result->fetch_assoc()) {
        $children = getTree($conn, $row['id']);
        if ($children) {
            $row['children'] = $children;
        }
        $tree[] = $row;
    }

    return $tree;
}

$tree = getTree($conn);
print_r($tree);

$conn->close();
?>