$ stmt-> fetch（）不能输入while

Question

I have write simple code in PHP, I'm a beginner in this language.

This is my code:

$id = "prova";
$query = "SELECT DISTINCT id_item FROM Users WHERE id = ? LIMIT 1 ";


if ($stmt = $conn->prepare($query))
{
 $stmt->bind_param("s", $id);
 $stmt->execute();
 $stmt->bind_result($result);

 while ($stmt->fetch()) {
   $id_item = (int) $result;
 }

}

My problem is that the cycle while is never executed, but I don't understand why. Thanks in advance.