it works !
Thank you very much Nick for the enlightment :)

Best regards
Andy

--- In firebird-support@yahoogroups.com, Nick Upson <nu@...> wrote:
>
> Hi,
>
> becuase you cannot do xx=NULL, you would need xx is null
>
> select count(*) from customer where ascii_val(substring(upper(fname) from 1
> for 1 )) is NULL
>
> I expect would work, or
>
> select count(*) from customer where fname is NULL ;
>
>