Limit clause not using index

Hi,

I have a very simple query on a big table. When I issue a "limit"
and/or "offset" clause, the query is not using the index.
Can anyone explain me this ?

rvponp=# explain select * from tblprintjobs order by loginuser,
desceventdate, desceventtime offset 25 limit 25 ;
QUERY PLAN
------------------------------------------------------------------------
-----------
Limit (cost=349860.62..349860.68 rows=25 width=206)
-> Sort (cost=349860.56..351416.15 rows=622236 width=206)
Sort Key: loginuser, desceventdate, desceventtime
-> Seq Scan on tblprintjobs (cost=0.00..25589.36 rows=622236
width=206)
(4 rows)

rvponp=# explain select * from tblprintjobs order by loginuser,
desceventdate, desceventtime ;
QUERY PLAN
------------------------------------------------------------------------
-----
Sort (cost=349860.56..351416.15 rows=622236 width=206)
Sort Key: loginuser, desceventdate, desceventtime
-> Seq Scan on tblprintjobs (cost=0.00..25589.36 rows=622236
width=206)
(3 rows)

Met vriendelijke groeten,
Bien à vous,
Kind regards,

Yves Vindevogel
Implements