$dsn = "mysql:host=localhost;dbname=test;charset=utf8mb4";
$user = "root";
$pass = "123456";
try {
    $pdo = new PDO($dsn, $user, $pass);
    echo "连接成功，准备写土味SQL！";
} catch (PDOException $e) {
    echo "连接失败：" . $e->getMessage();
}
?>

[/span>form action="db.php" method="post"
  [/span>button type="submit"点我，让HTML向MySQL说Hibutton
form