Re: Null in subquery returns no records

What is the difference between a null, an "unknown value," and a null set?

Is a null set an empty set?

If a null set means "a set with an unknown set of values", then what good does that do us from a logical perspective. Isn't that set as worthless as an unknown value?

What is returned from a null set if you don't use nulls?

How does a null set help keep fidelity to two-value logic?

Thanks,

Dan

"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message news:c02sjp$q4n$1_at_news.netins.net...
> "Jonathan Leffler" <jleffler_at_earthlink.net> wrote in message
> news:z%0Vb.17554$uM2.2847_at_newsread1.news.pas.earthlink.net...
> > Mike MacSween wrote:
> > > New testing rule for Mike - always test with null values.
> >
> > Alternative rule - always ensure the database stores no nulls!
> >
> > Not necessarily easy - but a good discipline.
> >
> <snip>
> And perhaps the best option of all -- use one of the databases that
employs
> a two-valued logic, with NULLs treated as null sets -- much cleaner and
> clearer. Examples are jBASE from www.jbase.com , Revelation from
> www.revelation.com and the U2 databases (UniData and UniVerse) from
> www.ibm.com (then do a search). You would not be alone as there are over
> 100,000 companies that use these products (could be a low estimate).
>
> I'm sure there are others as well that have avoided many of the SQL and
> RDBMS complications. There is nothing holy nor scientifically more
correct
> about the RDBMS model than many other possibilities. If you have an
> opportunity to free yourself of the notion that an RDBMS is required, you
> are likely to find a more productive environment elsewhere.
>
> Just thought I'd toss in my two cents even though most people who share
this
> opinion keep it quiet. --dawn
>
>
Received on Sat Feb 07 2004 - 21:14:29 CET