In VFP it changes from version to version. Some older versinons handled NULLs incorrectly (bugs) but it should be the same in VFP9 as in SQL Server.

>The second case is new for me. I never worried with NULLs in docid and I don't rememeber to have
>any problem. Do you now if this behavior occurs with dbf or just with SQL SERVER( that's why I thought that it could be a special configuration for NULL's)