Problem with items value

Question

Hi All,
I created 2 popup lov items exactly the same: P91_SUBJ_TYPE and P91_SHG_KOD.
I thought that they both has the same defult value (befoer selection value
from the LOV) :NULL. (although i haven't define any defult value).
now under Page Processing i have a process like this :
begin
if :P91_SHG_KOD is null and :P91_SUBJ_TYPE is not null then
     :P91_IND_FETCH :=1;
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE is null then
     :P91_IND_FETCH :=2;
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE is not null then
     :P91_IND_FETCH :=3;
end if;
end;but it doesn't work.
after some checks i found out that apex doesn't identify P91_SUBJ_TYPE as
null (although it looks that in the session state it is a null).but it does
recognize the item P91_SHG_KOD as null.
now in P91_SUBJ_TYPE item i defined a default value = 0.
and changed the process like this:
begin
if :P91_SHG_KOD is null and :P91_SUBJ_TYPE != 0 then
     :P91_IND_FETCH :=1;
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE =0 then
     :P91_IND_FETCH :=2;
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE != 0 then
     :P91_IND_FETCH :=3;
end if;
end;this process works fine.
my question why P91_SHG_KOD identified as null and P91_SUBJ_TYPE doesn't.
the question is bigger when i tried to do a computations for P91_IND_FETCH
(without any definition of default value for the l.o.v items)
computations for P91_IND_FETCH equals 1 when
     (:P91_SUBJ_TYPE !=0 or :P91_SUBJ_TYPE is not null)
and (:P91_SHG_KOD is null or :P91_SHG_KOD=0 )which works fine.
computations for P91_IND_FETCH equals 2 when
     (:P91_SHG_KOD !=0 or :P91_SHG_KOD is not null)
and (:P91_SUBJ_TYPE  is null or :P91_SUBJ_TYPE =0 )does not work.
can someone explain what seems to be the problem ?
thanks in advance

Answer 1

thank you for your response .
but it's doesn't works.
first - if apex doesn't return null value for LOV, why P91_SHG_KOD works as null ?
second - while i did the computation that you wrote it doesn't work:
begin
if :P91_SHG_KOD is null and :P91_SUBJ_TYPE is not null then
     :P91_IND_FETCH :=1;
/* it works well.*/
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE is null then
     :P91_IND_FETCH :=2;
/*it doesn't work. ind_fetch=3 (instead of 2).*/
end if;
if :P91_SHG_KOD is not null and :P91_SUBJ_TYPE is not null then
     :P91_IND_FETCH :=3;
/* it also works well.*/
end if;
end;and when P91_SHG_KOD and :P91_SUBJ_TYPE are empty it also doesn't work - ind_fetch =1 (instead of null)
in the 2 cases that it doesn't work(as i mentioned above) it also show an eror message:
Error: ORA-01722: invalid number performing LOV query:
"select K_DESC, KOD_P from (select kod_p || ' ' || kod_desc
k_desc, kod_p from codes order by kod_p) wwvlovinlineviewname where
KOD_P = :WWV_LOV_RETURN_KEY_UTIL_1111".  (this eror message caused because of the null problem. when i changed the process and defined a default value
to :P91_SUBJ_TYPE this message doesn't appear ).
can you explain me that?
thanks in advance.