Sikkerhed i PHP

PHP kode 

 <?php
    $data = "hans";
    $result->prepare("INSERT INTO elever(navn)VALUES(?)");
    $result->bind_param("s", $data);
    $result->execute();
    $result->close();
 ?>

PHP kode 

 <?php
    $id = 1;
    $result->prepare("SELECT * FROM elever where id=?");
    $result->bind_param("i", $id);
    $result->execute();
    $result->bind_result($id, $navn);
    while ($row = $result->fetch()) {
         printf ($id, $navn);
     }
 ?>

PHP kode 

 $result->prepare("INSERT INTO elever(navn, alder)VALUES(?, ?)");
     $result->bind_param("s", $data);
     $result->bind_param("e", $data2);