Hi,
thanks a lot.
All is ok now.
regards,
ivan.
Stephan Szabo wrote:
> On Sat, 13 Dec 2003, pginfo wrote:
>
> > Hi,
> >
> > I am using pg 7.4.
> >
> > Pls, see this test:
> >
> > tt07=# update a_cars set dog_or_free=0 where virtualen=0 and
> > dog_or_free=4 and ids NOT IN ( select oc.ids_car_real from a_oferti_cars
> > oc,a_oferti o where oc.IDS_oferti=o.ids and o.date_valid>=9964) AND
> > IDS = 'SOF_9989';
> > UPDATE 0
> > tt07=# update a_cars set dog_or_free=0 where virtualen=0 and
> > dog_or_free=4 and ids IN ( select oc.ids_car_real from a_oferti
> > _cars oc,a_oferti o where oc.IDS_oferti=o.ids and o.date_valid>=9964)
> > AND IDS = 'SOF_9989';
> > UPDATE 0
> > tt07=# update a_cars set dog_or_free=0 where virtualen=0 and
> > dog_or_free=4 and ids NOT IN ( select oc.ids_car_real from a_oferti_cars
> > oc,a_oferti o where oc.IDS_oferti=o.ids and o.date_valid>=9964 AND
> > OC.IDS_CAR_REAL IS NOT NULL) AND IDS = 'SOF_9989';
> > UPDATE 1
> >
> > I think IN is not working correct in this case.
>
> A NOT IN (subselect) when the subselect contains a NULL cannot ever return
> true by specification.
>
> --------------
> A NOT IN (subselect) -> NOT (A IN (subselect))
> NOT (A IN (subselect)) -> NOT (A = ANY (subselect))
>
> The result of A = ANY (subselect) is derived by the application of the
> implied comparison predicate, R = RT for every row RT in the subselect.
>
> If the implied comparison predicate is true for at least one row RT then A
> = ANY (subselect) is true. If the subselect is empty or the implied
> predicate is false for every row RT then A = ANY (subselect) is false.
> Otherwise it is unknown.
>
> For the one element row RT, A = RT where RT is a NULL returns unknown.
> Therefore, we know that it's not an empty subselect (it returns at least
> one row containing NULL -- that's our precondition), and that it does not
> return false for every row, so A = ANY (subselect) is either true or
> unknown depending on whether there's another row which does match, so
> NOT(A = ANY(subselect)) is either false or unknown.
