slette indhold når man updater

PHP kode 

 <?php
         $id = $_GET['id'];
         $result = mysql_query("SELECT * FROM `books` WHERE id = $id");       
         while($row = mysql_fetch_array($result))
         {
         ?>
             <form method="post" action="updaterindhold.php">
                 <input name="id" value="<?php echo $row['id'];?>" type="hidden">
                 <input type="titel" name="Titel" placeholder="<?php echo $row['titel_indhold'];?>" value="<?php echo $row['titel_indhold'];?>">
                 <br>
                 <input type="titel" name="FK_genre" placeholder="<?php echo $row['FK_genre'];?>" value="<?php echo $row['FK_genre'];?>">
                 <br>
                 <input type="titel" name="forfatter" placeholder="<?php echo $row['forfatter'];?>" value="<?php echo $row['forfatter'];?>">
                 <br>
                 <textarea name="tekst" style="width:400px; height:350px;" placeholder="<?php echo $row['tekst'];?>"></textarea>
                 <br>
                 <input type="submit" name="updater" value="Updater indhold">
             </form>
         <?php
         }
         ?>

PHP kode 

 <?php
 
 
 $mysql_hostname = "localhost";
 $mysql_user = "root";
 $mysql_password = "";
 $mysql_database = "uge10_opgave";
 
 
 $con = mysql_connect($mysql_hostname, $mysql_user, $mysql_password) or die("Could not connect database");
 mysql_select_db($mysql_database, $con) or die("Could not select database");
 
 // Prøv med 'latin1' hvis dette ikke virker.
   mysql_set_charset('utf8');
   
 
 if (isset($_POST['updater'])) {
     $id = $_POST["id"];
     $titel_indhold = $_POST['titel_indhold'];
     $FK_genre = $_POST['FK_genre'];
     $forfatter = $_POST['forfatter'];
     $tekst = $_POST['tekst'];
     
         $bruger = mysql_query("SELECT * FROM books");
         $sql = "UPDATE books SET titel_indhold='$titel_indhold', FK_genre = '$FK_genre', forfatter = '$forfatter', tekst = '$tekst' WHERE id = $id";
         $tabledata = $sql; echo $sql;
         $resultat = mysql_query($tabledata) or die (mysql_error());
                  
         if (mysql_affected_rows() > 0) {
             echo "Hej";
         }
     else {
         echo "Hej";
     }
 }   
 else {
     echo "Der ske ingen ting";
 }
     
 ?>