real_escape_string

$idset1 = rand() . "n";
$idset2 = rand() . "n";
if (!isset($_SESSION)) {
    session_start();
}

if (isset($_SESSION['username'])) {
    header('Location: index.php');
    exit();
}
if(isset($_POST['username']) && isset($_POST['password']) && isset($_POST['confirmpassword']) && isset($_POST['email'])){

    $username = mysqli_real_escape_string($con, $_POST['username']);
    $password = mysqli_real_escape_string($con, md5($_POST['password']));
    $confirmpassword = mysqli_real_escape_string($con, md5($_POST['confirmpassword']));
    $email = mysqli_real_escape_string($con, $_POST['email']);

    if($password != $confirmpassword){
        die("The confirmation password was not equal to the password.");
    }

    if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        die("The email entered was not correct.");
    }

    $result = mysqli_query($con, "SELECT * FROM `users` WHERE `username` = '$username'") or die(mysqli_error($con));
    if(mysqli_num_rows($result) > 0){
        die("This username already exists.");
    }


    $result = mysqli_query($con, "SELECT * FROM `users` WHERE `email` = '$email'") or die(mysqli_error($con));
    if(mysqli_num_rows($result) > 0){
        die("This email already exists.");
    }

    $result = mysqli_query($con, "SELECT * FROM `users` WHERE `id` = '$idset1'") or die(mysqli_error($con));
    if(mysqli_num_rows($result) > 0){
        $idset1 = $idset1 + $idset2;
        $result = mysqli_query($con, "SELECT * FROM `users` WHERE `id` = '$idset1'") or die(mysqli_error($con));
        if(mysqli_num_rows($result) > 0){
            die("An error ocurred, please retry");
        }
    }

    $ip = mysqli_real_escape_string($con, $_SERVER['REMOTE_ADDR']);
    $date = date('Y-m-d');

    mysqli_query($con, "INSERT INTO `users` (`id`, `username`, `password`, `email`, `date`, `ip`) VALUES ('$idset1', '$username', '$password', '$email', '$date', '$ip')") or die(mysqli_error($con));

    mysqli_query($con, "INSERT INTO `ads_urls` (`acc_id`) VALUES ('$idset1')") or die(mysqli_error($con));

    mysqli_query($con, "INSERT INTO `nodes` (`id_ass`, `active`) VALUES ('$idset1', '0')") or die(mysqli_error($con));

    header("Location: login.php?action=registered");