Adding Additonal Usergroup

[jacob115]

Here is a code to change the username of a user via mysql and php.

$vbulletin->db->query_read("update " . TABLE_PREFIX . "user set `username`='".addslashes($new_username)."', `$pointfield`=$points-$amount where userid='$userid'");

If that code successfully adds a username in my point system, what would add an additonal usergroup? I would enter the ID of the additional usergroup somewhere in the code I know, what would be the code to add an additional usergroup?