PHPを使用してデータベースに接続するにはどうすればよいですか?

$servername = "localhost";
$username = "username";
$password = "password";
$database = "dbname";

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

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

echo "成功连接到数据库";

$host = "localhost";
$port = "3306"; // MySQL 的默认端口
$dbname = "dbname";
$username = "username";
$password = "password";

$dsn = "mysql:dbname=$dbname;host=$host;charset=UTF8;port=$port";

try {
    // 创建连接
    $conn = new PDO($dsn, $username, $password);
    // 设置错误信息模式
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "成功连接到数据库";
} catch (PDOException $e) {
    echo "连接失败: " . $e->getMessage();
}

$host = "localhost";
$database = "dbname";
$username = "username";
$password = "password";

// 创建连接
$conn = new PDO("mysql:host=$host;dbname=$database", $username, $password);

// 创建准备语句
$stmt = $conn->prepare("SELECT * FROM users");
$stmt->execute();

// 遍历结果
while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo "ID: " . $result['id'] . ", 名称: " . $result['name'] . "<br>";
}

$dsn = "mysql:dbname=mydb;host=localhost";
$conn = new PDO($dsn, $username, $password);

$userId = 1;

// 查询语句
$stmt = $conn->prepare("SELECT * FROM users WHERE id = ?");
$stmt->bind_param("i", $userId); // i 表示整数
$stmt->execute();

// 获取结果
$result = $stmt->get_result();

if ($row = $result->fetch_assoc()) {
    echo "名称: " . $row['name'] . "<br>";
    echo "电子邮件: " . $row['email'] . "<br>";
} else {
    echo "没有找到用户";
}

$conn->close();