Dmitry,

I don't know whether it's bad or unconventional design.

All I can say is that I have done it and probably will

It makes life easier.

- The relationship is not optional any more
- No need for outer joins
- If you need a 'real' parent - you can always check for that value

>I am wondering if the following approach would be considered bad or unconventional design.
>
>Say I leave one row in every parent table with the entry in the unique column/field empty. The reason I am considering this approach is that it will allow me to have an empty entry in the foreign keys as well.
>
>What do you think?