> this query return 0
>
> SELECT count(*) FROM RDB$DATABASE WHERE ((CAST(NULL AS INTEGER) IS NULL AND CAST(123 AS INTEGER) IS NULL) OR
> (CAST(NULL AS INTEGER)=1))
>
> when i add "NOT" this query return also 0
>
> SELECT count(*) FROM RDB$DATABASE WHERE NOT ((CAST(NULL AS INTEGER) IS NULL AND CAST(123 AS INTEGER) IS NULL) OR
> (CAST(NULL AS INTEGER)=1))
>
>
> is this a bug?

No. Where clause of the first select is
True and False or Null -> Null
So the second select is
Not Null -> Null

Ivan