从db中检索数据并将其显示在php中的表中..看到这段代码有什么问题吗？

<?php
// 建立数据库连接
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("数据库连接失败: " . $conn->connect_error);
}

// 执行查询语句
$sql = "SELECT * FROM table_name";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据表格
    echo "<table>";
    echo "<tr><th>列1</th><th>列2</th></tr>";
    while ($row = $result->fetch_assoc()) {
        echo "<tr><td>" . $row["column1"] . "</td><td>" . $row["column2"] . "</td></tr>";
    }
    echo "</table>";
} else {
    echo "没有找到数据";
}

// 关闭数据库连接
$conn->close();
?>