Sende flere værdier med en GET form

Kode 

<form action='ret.php' method='GET' name='header'>Ret overskriften til: 
<input type='hidden' name='id' value='5'/>
<input type='text' name='header' value=''/>
<input type='submit' value='Ret' />
</form>

Kode 

$sql = "UPDATE mobil SET header='$header' WHERE id=".$id;
$conn->query($sql);

Kode 

// A QUICK QUERY ON A FAKE USER TABLE
$query = "SELECT * FROM `users` WHERE `status`='bonkers'";
$result = $mysqli->query($query) or die($mysqli->error.__LINE__);

Kode 

// query
$sql = "SELECT title FROM books ORDER BY title";
$q   = $conn->query($sql);
if(!$q){
  die("Execute query error, because: ". $conn->errorInfo());
}