在导入数据之前对MySQL数据库列使用php函数

$stmt = $pdo->prepare('INSERT INTO users (username, password) VALUES (:username, :password)');
$stmt->bindParam(':username', $username);
$stmt->bindParam(':password', $password);
$username = $_POST['username'];
$password = password_hash($_POST['password'], PASSWORD_DEFAULT);
$stmt->execute();

$username = trim($_POST['username']);
if (!preg_match('/^[a-zA-Z0-9_]+$/', $username)) {
    die('Invalid username');
}

try {
    $pdo->beginTransaction();
    for ($i = 0; $i < count($data); $i++) {
        $stmt = $pdo->prepare('INSERT INTO users (username, password) VALUES (?, ?)');
        $stmt->execute([$data[$i]['username'], password_hash($data[$i]['password'], PASSWORD_DEFAULT)]);
    }
    $pdo->commit();
} catch (Exception $e) {
    $pdo->rollBack();
    echo 'Failed: ' . $e->getMessage();
}