YegiZavr

$login = filter_var(trim($_POST['login']),
FILTER_SANITIZE_STRING);

$pass = filter_var(trim($_POST['pass']),
FILTER_SANITIZE_STRING);

$mysql = new mysqli('localhost','user','pass','db');

$result = $mysql->query("SELECT * FROM `users` WHERE `login` = '$login' AND `pass` = '$pass'");

$user = $result->fetch_assoc();

if(count($user) == 0){
echo "User does not exist";
exit();
}