我需要一个mysql数据库连接类

以下是一个简单的MySQL数据库连接类的示例代码：

class MySQLDatabase {
    private $host = "localhost";
    private $username = "username";
    private $password = "password";
    private $database = "database";
    private $connection;

    public function __construct() {
        $this->connection = mysqli_connect($this->host, $this->username, $this->password, $this->database);
        if (!$this->connection) {
            die("Connection failed: " . mysqli_connect_error());
        }
    }

    public function query($sql) {
        $result = mysqli_query($this->connection, $sql);
        if (!$result) {
            die("Query failed: " . mysqli_error($this->connection));
        }
        return $result;
    }

    public function escapeString($string) {
        return mysqli_real_escape_string($this->connection, $string);
    }

    public function numRows($result) {
        return mysqli_num_rows($result);
    }

    public function insertId() {
        return mysqli_insert_id($this->connection);
    }

    public function __destruct() {
        mysqli_close($this->connection);
    }
}

使用方法：

$db = new MySQLDatabase();
$sql = "SELECT * FROM users";
$result = $db->query($sql);
while ($row = mysqli_fetch_assoc($result)) {
    echo $row['username'] . "<br>";
}