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

Alexandr Savinov wrote:
> JOG schrieb:

> But what if some
> other object we need to add is known in advance to have no colour at
> all? A formal criteria for "does not have a colour" is that we do not
> want to see it when we select objects along dimension COLOUR.
>
> Theoretically, we might define such a structure of tables that this
> situation is excluded. Practially, it is almost impossible so we need to
> permit null value as an indication that some column is inappropriate
> for this object (and this object will be invisible from the side of this
> column).
>

If an "object" lacks the attribute of colour then surely it ought to be modelled by a relvar that doesn't have a colour attribute. Can you explain why this would be "almost impossible" given that you also said this fact is known in advance?

-- 
David Portas 
SQL Server MVP 
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