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


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Re: CONCAT(null, "something") == NULL ?
Alan Gates 2012-11-05, 16:16
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
>>
>>