> This indeeds performs good (about 10000 times faster then select number,url > from mm_mediasources order by number desc limit 20) . But hardly beautiful, > and quite useless too because of course I am now going to want to use an > offset (limit 20 offset 20, you see..), which seems more or less impossible > in this way, isn't it.
Yes, and the offset is a good reason why PostgreSQL will not be able to do it by itself either.
Is "number" unique across the board?
If so, instead of the offset you could use WHERE number > $lastValue.