Update SQL tables through php form
$link = mysqli_connect("$server", "$user", "$pass", "$webdb");
$username = mysqli_real_escape_string($link, (string) $_POST['username']);
$displayname = mysqli_real_escape_string($link, (string) $_POST['display_name']);
$email = mysqli_real_escape_string($link, (string) $_POST['email']);
$password = sha1((string) $_POST['password']);
$query="INSERT INTO user (`username`, `nicename`, `email`, `password`)
VALUES ('$username', '$displayname', '$email', '$password', '1')";
mysqli_query($link, $query);
mysqli_close($link);
echo $query;
?>

INSERT INTO user (username, nicename, email, password) VALUES ('orion5814', 'Orion5814', 'my@abc.com', '72f2ac484bee398758e769530dd56228d905884d', '1')

$username = $link->real_escape_string($_POST['username']);

$link->query($query);
$link->close();

$link = mysqli_connect("$server", "$user", "$pass", "$webdb") or die( "Error:" . mysqli_connect_error());

mysqli_query($link, $query) or die ("Error:" . mysqli_error($link));