Re: Complete axiomatization of relational algebra

"Neil Nelson" <n_nelson_at_pacbell.net> wrote in message news:3A8DDF4E.CCEEC550_at_pacbell.net...
> elements each having a uniform set of properties. I.e., we should be able
 to
> `denormalize' to a single table. The primary operation on this table is
to ask

I've never carried out this 'denormalization', so what follows is speculative.

I think that, in order to completely denormalize a schema to a single table, you need to allow outer joins as well as inner joins and unions. When you carry out outer joins, you can get some NULLS in some columns.

An interesting exercise, occasionally, is to take a column that permits NULLS and discover a pair of decomposed tables and an outer join that would have resulted in the single table with optional column we were given.

I did this exercise a few times. It resulting in my discovery of more and more about less and less, until I finally knew a lot about nothing at all! ;) ;) ;) Received on Sat Feb 17 2001 - 08:14:48 CET