php中mysql递归函数返回值

<?php
// 连接数据库
$conn = new mysqli("localhost", "username", "password", "database");

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

// 递归函数查询层级数据
function getHierarchy($id, $conn) {
    $sql = "SELECT id, name, parent_id FROM categories WHERE id = ?";
    $stmt = $conn->prepare($sql);
    $stmt->bind_param("i", $id);
    $stmt->execute();
    $result = $stmt->get_result();
    $row = $result->fetch_assoc();

    if ($row) {
        echo $row['name'] . "\n";
        if ($row['parent_id'] != 0) {
            getHierarchy($row['parent_id'], $conn);
        }
    }
}

// 调用递归函数
getHierarchy(3, $conn);

// 关闭连接
$conn->close();
?>