> Thank you Ivan,
> (Diki :-))

Prosim :-)

> but I want make select like this (weekly summary) :
>
> select extract(week from datum) as w, sum(some_data) as total
> from t
> where ...
> GROUP BY extract(week from datum)

There are several possibilities how to achieve this,
but as Helen pointed out, you have to tell your requirements *exactly*.
E.g. 1-1-2006 is Sunday, so according to iso standard
it actually belongs to last week of 2005. What restul do you expect
this week-function to return ?

Ivan