$insert=$db->query("INSERT INTO kullanicilar SET mail='{$mail}', pass='{$pass}' );

if(isset($_POST["register"])) {
  $mail     = htmlspecialchars($_POST["mail"]);
  $username =  htmlspecialchars($_POST["username"]);
  $pass     =  htmlspecialchars($_POST["pass"]);
  $pass2    =  htmlspecialchars($_POST["pass2"]);

  if (empty($mail) || empty($username) || empty($pass) || empty($pass2)) {
    header("Location:../register?bos=var");
  }else{
    $kullanicivarmi = $vt->prepare("select * from uyeler where username=? || mail=?");
    $kullanicivarmi-> execute(array($username,$mail));
    $varmi          = $kullanicivarmi->rowCount();
    if ($varmi>0) {
      header("Location:../register?durum=var");
    }else{
      if ($pass==$pass2) {
        $pass     =md5(htmlspecialchars($_POST["pass"]));
        $pass2    =md5(htmlspecialchars($_POST["pass2"]));
        $kullaniciekle= $vt->query("INSERT INTO uyeler SET email='{$mail}', username='{$username}', pass='{$pass}' )";
        $ekle = $kullaniciekle->execute(array('email'=>$mail, 'username'=>$username, 'pass'=>$pass)); 
        if ($kullaniciekle) {
          header("Location:../login"); 
        }else{
          header("Location:../register?durum=olmadi");
        }
      }else{
        header("Location:../register?sifre=olmadi");
      }
    }
  }
}