insert in database

<?php

require_once 'DB_info.php';
require_once 'UTILS.php';

$alienname = $_POST['alienname'];
$email =$_POST['email'];
$uUsername =$_POST['ausername'];
$upassword =$_POST['apassword'];


$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT alienname FROM $myAliens WHERE alienname='$alienname'";
$result = $conn->query($sql);

checkErrorReturn
    ($result->num_rows > 0,
     "An alien with this name is already registered!",
     "Back to registration page",
     "register.html");

$sql ="INSERT INTO `myaliendb`.`myaliens` (`alienname`, `Email`, `Username`, `Password`) VALUES ('$alienname', '$email', '$uUsername', '$upassword')";
if ($conn->query($sql) === TRUE) {
    echo "New user has been created.";
    echo " Back to <a href= 'index.html'>login<a>";
} else {
    echo "error";
}

$conn->close();

$thisAlienDir = $alienPicturesDir . "/" . $alienname;

checkErrorReturn
    (! mkdir($thisAlienDir,0700),
     "Could not create directory $thisAlienDir.",
     "Back to registration page",
     "register.html");

echo "<h1> Welcome $alienname! You were successfully
registered! </h1>";

echo '<h1> <a href="index.html"> Go to the signin page </a> </h1>';






?>