[kh99]

I haven't tried these, but I think there's two things you can do: when a column is auto increment, you don't want to supply a value but you can put NULL as a placeholder. You can put NULL where you'd put a column name in a select, and that value will always be null. So I think this would work:

        $db->query_write("
            INSERT INTO ".TABLE_PREFIX."unsub_subscribethread
            SELECT NULL,
                   userid,
                   threadid,
                   emailupdate,
                   folderid,
                   canview
            FROM ".TABLE_PREFIX."subscribethread
            WHERE userid = '$id'
            AND emailupdate IN (1, 2, 3)");

The other way would be to list each column and leave out the id column, like:

        $db->query_write("
            INSERT INTO ".TABLE_PREFIX."unsub_subscribethread
                (userid, threadid, emailupdate, folderid, canview)
            SELECT userid,
                   threadid,
                   emailupdate,
                   folderid,
                   canview
            FROM ".TABLE_PREFIX."subscribethread
            WHERE userid = '$id'
            AND emailupdate IN (1, 2, 3)");

BTW, for future reference you can see some of this in the mysql manual, for instance here's the page for the INSERT statement: http://dev.mysql.com/doc/refman/5.0/en/insert.html