Ciao, una domanda......... ma se volessi far comparire un form per proseguire solo nel caso che il pin sia stato trovato nella tabella "serial" e inserito nella tabella "serialusati" e non farlo comparire in tutti gli altri casi, come devo fare?

questo è il codice:

Codice PHP:
<?php 

// dati per la connessione al database 

$db_host       = "localhost"; 
$db_user       = "root"; 
$db_password   = ""; 
$db_name       = ""; 

// mi connetto al database 

$db            = mysql_connect ($db_host, $db_user, $db_password) or die ('Impossibile accedere al database!'); 
$db_forum      = mysql_select_db ($db_name, $db); 

// Verifico se il pin è presente nel db 

$numero = $_POST['pin']; 
$query = mysql_query("SELECT * FROM serial WHERE pin = '$pin' "); 
$num = mysql_num_rows($query); 
if ($num > 0) 
{ 
$query         = "INSERT INTO `serialusati` (pin) 
                  VALUES ('".$_POST['pin']."')";                
$query         = "DELETE FROM serial WHERE pin=$pin";   
}                 
else 
echo "Il pin inserito non è valido!"; 
$query_results = mysql_query($query) or die(""); 

?>
questo è il form:

Codice PHP:
<FORM method="post" action="index.php">
                        <table width="55%" border="0" align="center" cellpadding="0" cellspacing="0">
                          <tr>
                            <td colspan="3"></td>
                          </tr>
                          <tr> 
                            <td colspan="3"><div align="center"><font color="#000000">Questo 
                                &egrave; il numero che hai inserito &egrave; valido.</font></div></td>
                          </tr>
                          <tr> 
                            <td width="28%"></td>
                            <td width="39%"><input name="uname" type="hidden" id="uname" value="<? echo "$pin"; ?>"></td>
                            <td width="33%"></td>
                          </tr>
                          <tr> 
                            <td></td>
                            <td></td>
                            <td></td>
                          </tr>
                          <tr> 
                            <td><div align="center">Pin N&deg;:</div></td>
                            <td><? echo "$pin"; ?></td>
                            <td><input name="submit" type="submit" class="form8" value="Prosegui&gt;"></td>
                          </tr>
                          <tr> 
                            <td><div align="center"></div></td>
                            <td></td>
                            <td></td>
                          </tr>
                          <tr> 
                            <td></td>
                            <td></td>
                            <td></td>
                          </tr>
                        </table>
                        

</p>
                        

</p>
                      </FORM>
Grazie per l'aiuto