If not is not a value permitted, as I can understand by your desire of converting it in something different, preventi it at database level.
So you can:
a)- set the column as NOT NULL
b)- set a default for the column
c)- set it's value, if null, to default value in a before insert and before edit trigger

If you are accessing the database with IBObject native components (IB_), you can set "getserverdefaults" dataset property and skip step c)

Regards
Marco Menardi

--- In ib-support@y..., "jyotindra_bhoyania" <jyotindra_bhoyania@y...> wrote:
> Dear Friends,
>
> I am stuck in problem.
>
> How to check Null Values.
> Is there some Function for Null. (For example in oracle their is NVL
> function).
> How many bites does Firebird Interbase (6) stores for NULL values.
> Please help for check null values and replaceing null values with
> zero.
>
> waiting for promt reply.
>
> Thank's
> jyotindra.