Select every first/last record of a partition?

Hi,

suppose a table that has records with some ID and a timestamp.

id, ts
3, 2012/01/03
5, 2012/01/05
7, 2012/01/07
3, 2012/02/03
3, 2012/01/05
5, 2012/03/01
7, 2012/04/04

to fetch every last row of those IDs I do:

select id, ts
from ( select id, ts, row_number() over ( partition by id order
by ts desc ) as nr from mytab ) as x
where nr = 1

Is there a another way without a subselect?
There might be more columns so the window-functions first/last won't help.