Re: So what's null then if it's not nothing?

paul c wrote:
> vc wrote:

[...]
> > I am not sure, as I said before, that the data type is so terribly
> > important for storing data. TTM does not provide any rationale for the
> > must-be-supported data type.
> > ...
[...]
> For one thing, the only way, without going outside the relational
> operators (eg. without counting returned 'rows' or checking 'return
> codes' or 'status codes') to find out if a relation has any true
> propositions .

I am not sure what you mean by the above. Could you please elaborate ?

>is to support a value such as 'TRUE'
> I believe TTM
> effectively considers TRUE to be equivalent to a projection over zero
> columns of a non-empty relation. Basically, it seems to be TTM's way of
> being able to give an answer within the algebra that supports FOL's
> existential quantifier, ie. the result of the question is in fact a
> relation.

Could you rephrase that and provide an example ? Also, when is the result of a question ( a query ?) not a relation ?

>
> I'd say that ought to be rationale enough, but there do seem to be some
> related practical uses of tables with no columns.
>
> cheers,
> p
Received on Mon Dec 05 2005 - 19:47:42 CET