sql update example php code

//include 'dbc.php';
//session_start();
$user_ip = $_SERVER['REMOTE_ADDR'];

$id = $_SESSION['user_id'];


$sql_insert1 = "UPDATE `users`
SET `last_online` = now(),
`users_ip` = '$user_ip'
WHERE (users.id = $id)
";
mysql_query($sql_insert1) or die("Insertion Failed:" . mysql_error());

?>