Fetch and match data from 2 tables?

[marcus123]

Thanks buddy for reply.

Here is what I mean. I have a table called Ads which has a column called tid right. This TID column stores tids that correspond to forum real TIDs

I would like to fetch all thread tids and then all ads tids compare them and then output Thread tids that are not in the Ads tid column.

$query = $db->query("
        SELECT t.tid
        FROM ".TABLE_PREFIX."threads t
        WHERE t.tid NOT IN (how to fetch ads tid from here)
    ");

When I fetch tids they all show like one long number. How to put a comma in the middle to use it in NOT IN expression

---

$query2 = $db->query("
        SELECT t.tid
        FROM ".TABLE_PREFIX."threads t
		WHERE t.tid NOT IN (SELECT a.tid
        FROM ".TABLE_PREFIX."ads a)
    ");

Is this OK to use? Looks ugly to me!