Hello,
I have a SQL query:


SELECT
CASE WHEN umowy.numer_umowy IS NULL THEN 0 END AS numer_umowy
FROM umowy
WHERE umowy.data_podpisania IS NOT NULL AND umowy.id_wnioski IN
(SELECT CASE WHEN wnioski.id_wnioski IS NULL THEN 0 END AS id_wnioski
FROM wnioski
LEFT JOIN kategorie_wnioskow ON
kategorie_wnioskow.id_kategorie_wnioskow=wnioski.id_kategorie_wnioskow
WHERE kategorie_wnioskow.id_kategorie_wnioskow_typ=1) AND umowy.rok=2014

How do I stop if "NUMER_UMOWY" is NULL is returned to "0" and not null

My database is Firebird 2.5