Extracting all the id's from a query and saving them as a comma seperated list

[eluser]jtotheb[/eluser]
I'm trying to run a query using AR and then save back to another table all the ID's from that query as a comma seperated list.

I'm trying to use array_pop($array) and then join (', ', $array) . ", and $last";

But i think the problem i'm having is getting the result correctly out of the query result.

If anyone could give me a wee hand with this, that would be fantastic!