How validate two select list in oracle apex - sql

Question

I'm using Oracle apex, and i have 2 select list components that get the elements from the same table. i want build a currency converter, and the list of currency are "divisas"
My problem is: i want validate that when on one select component, one value is selected, the other component doesn't contain that element from select list 1. And vice verse
Also when on select 1 is null on the select 2 must show all result from the table, and vice verse.
I start with this query, but i can't do it works
select *
from divisas
where EN_APP = 'S'
and (
case when :P12_DIVISA is not null then (cod_divi <> :P12_DIVISA) else EN_APP = 'S' end
)
;
can somebody help me?

Answer 1

There's the Cascading List of Values property for Select List items. However, as you want to handle both items at the same time, you'll enter circular reference & dead loop so it won't just work.
Here's an option which does what you wanted; see if it helps:
create two items, e.g. P59_CURR_1 and P59_CURR_2 (for two currencies)
their type is Select List item
Page action on selection = "Redirect and set value"
SQL query looks like this (for P59_CURR_1)
select cod_divi d, cod_divi r
from divisas
where cod_divi <> nvl(:P59_CURR_2, 'X') -- would be `:P59_CURR_1` for another item
order by cod_divi
don't set cascading list of values parent item!
That's it; run the page and see how it behaves. Looks OK to me on apex.oracle.com's Apex 20.1 version.