Página php con formulario html dentro ejecutar código php antes de completar el formulario

Prueba:

if(isset($_POST['Submit']))  {
    $user = "DB";
    $password = "";
    $host = "";
    $database = "my_DB";
    $connessione = mysql_connect($host, $user, $password);

    @mysql_select_db($database, $connessione) or die( "Unable to select database");

    $id = $_REQUEST['id'];
    $query = "INSERT INTO myTable (ID) VALUES ('".$id."')";
    mysql_query($query, $connessione);
    mysql_close();
}