Thank you, Fred Wilson, for your help. Now it works properly.
Sorry for this question. I am new in SQL Language, but that I should know.

Best regards
Walter Neumann

Am Freitag, 6. September 2002 18:30 schrieb Wilson, Fred:

> That chant, as it's been stated here a zillion times, is:
> NULL is a state, *not* a value...
> NULL is a state, *not* a value..
>
> Since NULL is a state (*not* a value) you can't check for it using '='
> *Nothing* will ever = NULL..
>
> Use "IS NULL" or "IS NOT NULL"
>
> Now repeat one more time:
>
> NULL is a state, *not* a value... ;)
>
> Best regards,
> Fred Wilson
> SE, Bell&Howell
> fred.wilson@...
>