$login = 'LOGIN_USER';
$db = mysqli_connect('127.0.0.1', 'root', '', 'dbname');
if(!$db)
return print_r('Error connect');
$query = "SELECT * FROM `userdatabase` WHERE `login` = '{$login}' LIMIT 1";
$result = mysqli_query($db, $query);
mysqli_close($db);
$result = mysqli_fetch_assoc($result);
if(!$result)
return print_r('User not found..');
return print_r('User found!');