Sampo Syreeni wrote:
> On 2006-10-05, David Cressey wrote:
>
>> An outer join between two relational tables will, in general, produce
>> a table with nullable columns.
>
> I'd add that the same applies if we want the relational model to be
> closed under arbitrary unions. To me that seems somehow more elementary,
> and it also ties neatly with inheritance modelling: even if you
> represent entities of subtypes and supertypes by different relations,
> sometimes it's handier to work on their union.
You are making a great blunder. Null is totally unecessary for handling
specialization and generalization.
Received on Thu Oct 05 2006 - 08:36:33 CDT
