>Hi Boris.
>
>>I just wandering why you allow NULLs in fields other then DateTime?
>
>I have two tables, and this field is used to create a relation between tables. The most cases, this relation have to exist, but in some cases, I can add a record in TableA, but I will not add a record in TableB.
>
>In this case, I have to keep the value NULL, or SQL will return an error. I'm starting with MS-SQL, maybe there is other way to do it, but I don't know!

If I understood you correctly TableA is the Parent table, right?