Re: Null in subquery returns no records

"ben brugman" <ben_at_niethier.nl> wrote in message news:402b402e$0$1414$4d4ebb8e_at_read.news.nl.uu.net...
>
> >
> > I was trying to emphasise the point that your selection of logical
> > rules is arbitrary. SQL picked one. There were others. And it's not
> > clear to me that any one of them is better than any other.
>
> First thanks for participating,
>
> And allthough I agree with you that 'sometimes' the choice of rules
> is arbitrary, I do not agree with that in this case.
>
> Starting from boolean logic.
>
> (False and (anything)) Evaluates to false.
> anything can only be True or false in boolean logic.
>
> Extending this to three valued logic and accepting that
> the null value is only used because we do not know the
> value, the logic example with anything in it stays the same.
> Therefore :
> (False and null) evaluates to false.
>
> I agree with you that the interpretation of null can be of
> several kinds. In your case the weight of a planet should
> exceed a certain minimum (why does an electron not count as
> a planet ?). So there is weight, we just don't know it.
> Or it could be an occurence in the future (a date) which has
> not occured yet so it is a data larger than now but we just do
> not know it.
> But I do realise that some people use null to represent a value
> outside the domain of the 'normal' values. In that case boolean
> logic does not apply and the three valued logic as implement
> in SQL can fall apart. I personaly think that allthough a value
> is unknown it should not be a value outside the domain.
> Example : store an age of somebody as from 0 to 99 and using
> null for ages above that range. I think that is wrong use of null.
>
> So I think the implementation of three valued logic as is in SQL
> (at least Oracle and MS-sql-server) is logical and the correct choice
> and it is not an arbitrare choice.

In that case, Ben, I can only conclude you have not bothered to examine NULL as specified for SQL. It is entirely arbitrary and inconsistent. Received on Thu Feb 12 2004 - 18:25:07 CET