Re: 3vl 2vl and NULL

Hugo Kornelis wrote:
> On 10 Dec 2005 05:22:38 -0800, dawn wrote:
>
> (snip)
> >> "Show me all family members who are NOT older than Aunt Marge" - should
> >> Uncle Vernon be included or not? Why?
> >
> >Two choices of how to ask the question --
> >1) Show me all members who have an age where that age is less than or
> >equal to Aunt Marge's age
> >
> >In this case Uncle Vernon does not show up because he does not have an
> >age
> >
> >2) Show me all family members who do not have an age greater than Aunt
> >Marge's
> >
> >In this case Uncle Vernon does show up
>
> Hi Dawn,
>
> So the results of the query would depend on exactly how you formulate
> it?

I cannot think of any situation where that is not the case, can you ;-)

> Hmmm. AFAICT, this means that in your 2VL algebra, missing data results
> in ~(A) not being the same as (~A).

No, I don't think so, but before I respond to more, can you give me an
example that makes you think this? Thanks. --dawn

.

Relevant Pages

  • Re: 3vl 2vl and NULL
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  • Re: 3vl 2vl and NULL
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  • Re: 3vl 2vl and NULL
    ... >>Hugo Kornelis wrote: ... Dot as everyone else, including Uncle Vernon in this 2VL scenario, has ... If the data are changed so that Aunt Marge also has a null set age, ...
    (comp.databases.theory)
  • Re: 3vl 2vl and NULL
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    (comp.databases.theory)
  • Re: 3vl 2vl and NULL
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