PHP 오류: 데이터베이스 솔루션에 연결할 수 없습니다.

<?php
$servername = "localhost";
$username = "root";
$password = "123456";
$dbname = "mydatabase";

$conn = new mysqli($servername, $username, $password, $dbname);

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

echo "连接成功";
?>

<?php
$servername = "localhost";
$username = "root";
$password = "123456";

$connection = @mysqli_connect($servername, $username, $password);

if (!$connection) {
    die("数据库服务器连接失败：" . mysqli_connect_error());
}
else {
    echo "数据库服务器连接成功";
}

mysqli_close($connection);
?>

<?php
if (!function_exists('mysqli_init') && !extension_loaded('mysqli')) {
    echo 'MySQLi扩展未加载';
}
else {
    echo 'MySQLi扩展已加载';
}

if (!function_exists('mysqli_connect')) {
    echo 'MySQLi函数未定义';
}
else {
    echo 'MySQLi函数已定义';
}
?>

<?php
$servername = "localhost";
$username = "root";
$password = "123456";
$dbname = "mydatabase";

$conn = new mysqli($servername, $username, $password, $dbname);

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

$sql = "SELECT * FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        echo "ID: " . $row['id'] . "，姓名: " . $row['name'] . "<br>";
    }
} else {
    echo "没有数据";
}

$conn->close();
?>