Compile a comma-separated list from a query

How to generate a comma-separated list from the following query? I assume to use a Repeat step containing a Set Value step. I don’t know how the Set Value step should be coded? Thanks.

SELECT id FROM topics WHERE forum_id=1 ORDER BY sticky DESC, last_post DESC, id DESC LIMIT 0, 30

You mean abc ,def , xyz ?

I assume the inbuilt Export CSV server action is not suitable for you?

SELECT group_concat(id) FROM topics WHERE forum_id=1
GROUP BY forum_id
ORDER BY sticky DESC, last_post DESC, id DESC LIMIT 0, 30