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Pig >> mail # user >> CONCAT(null, "something") == NULL ?


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Yang 2012-11-02, 22:09
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Alan Gates 2012-11-02, 22:33
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Cheolsoo Park 2012-11-02, 22:40
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Yang 2012-11-05, 17:15
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Alan Gates 2012-11-05, 16:16
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Re: CONCAT(null, "something") == NULL ?
I agree with Alan on all counts. I think the confusing part is that null is
overloaded. Alas.
2012/11/5 Alan Gates <[EMAIL PROTECTED]>

> Better in terms of semantics or terms of documentation?  We can't change
> the semantics of null in Pig; it's been that way the whole time.  Plus this
> concept of unknown data is important in data processing.  If we had it to
> do over again we could name it 'unknown' instead of null, but it seems late
> for that now.
>
> Alan.
>
> On Nov 2, 2012, at 3:40 PM, Cheolsoo Park wrote:
>
> > Hi Alan,
> >
> > Recently, I have seen several similar confusions about nulls in Pig. For
> > example, here is another discussion:
> > https://issues.apache.org/jira/browse/PIG-3021.
> >
> > We are documenting them, but apparently, many users find it confusing. I
> am
> > wondering if there is anything that we can do better.
> >
> > Thanks,
> > Cheolsoo
> >
> > On Fri, Nov 2, 2012 at 3:33 PM, Alan Gates <[EMAIL PROTECTED]>
> wrote:
> >
> >> To give some context, the null semantics in Pig follow SQL's.  In SQL,
> >> null is viral, so any operation with null results in null.  The idea is
> >> that null means unknown, not empty.  So concat('x', unknown) = unknown.
> >>
> >> Alan.
> >>
> >> On Nov 2, 2012, at 3:09 PM, Yang wrote:
> >>
> >>> looks a more intuitive result should be "something" , right?
> >>>
> >>> but on my system it gave null
> >>
> >>
>
>
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Cheolsoo Park 2012-11-02, 22:14