>>
>>BTW If the NULL values are NOT needed at all I prefer to set default value to empty field (depends of its type). Only type that allow NULLs is datetime :-)
>>Of course this is dependong the application, sometimes NULLs are mandatory.
>
>Borislav, I came across an issue with the NULLs and may have to adapt the same approach you have - setting default value instead of NULL. If you don't mind, I would like to ask you how you hide the record/row in the parent table with the empty/default field from the user? TIA.

You can't have more than one record in Parent table with DEFAULT value. Otherwise a PK constrain will raise an error.
How to hide it: Just use WHERE in your SELECT statement.

But I'm still wondering why you need child records w/o parent ones?