Search in Listbox exclude values starting 999 but include NULLs

[konHi]

Hi,

i have the following problem.

I have a table containing contracts: "CONTRACTS", a table "PERSON" is connected through ID_P.

CONTRACT: 

ID_V	ID_P	PRODUCT	VALUE
1	P1	PRODUCT 1	100
2	P1	PRODUCT 2	200
3	P2	PRODUCT 3	300
4	P2	PRODUCT 4	400
5	P4	PRODUCT 5	350
6		PRODUCT_ALL	500

PERSON:

ID_P	NAME	PERSGROUP
P1	PERSON 1	111
P2	PERSON 2	111
P3	PERSON 3	222
P4	PERSON 4	999

As a result i have 1 contract (ID_V = 6) with no PERSON.

Now I want to receive all Contracts with Persons without 999 but included NULL.

I tried to search in PERSGROUP for -999 but NULL disappears.

I receive the right amount if I search in ID_V for "=COUNT(IF(PERSGROUP <> '999',ID_V))". In my opinion: "no business user will be able to create this kind of search filter".

I could also add "null"-PERSON to PERSON Table and x-more tables with possible "null"-Dimensions. But is there a more user friendly and less data modell change demanding solution? Search in PERSGROUP like "(-999|ISNULL) or something like that?

I really appreciate your answer.

Konstantin