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https://issues.apache.org/jira/browse/PIG-1922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009721#comment-13009721
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Alan Gates commented on PIG-1922:
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bq. 3. Use of (in)equality operator with NULL results in UNKNOWN (which is not
the same as NULL)
For all intents and purposes, unknown is the same as null here. Filters pass
through only records that are true. The result of a boolean comparison with a
null does not pass through the filter. So it is fine to say x == null results
in null.
So I'm not sure there's a bug here at all. x == null is probably not what the
user meant, but as long as the filter passed no records through we did the
right thing.
> null is being treated as string constant in expressions
> -------------------------------------------------------
>
> Key: PIG-1922
> URL: https://issues.apache.org/jira/browse/PIG-1922
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.8.0, 0.9.0
> Reporter: Thejas M Nair
> Fix For: 0.9.0
>
>
> In following statement, the null gets translated to string constant. The
> statement is invalid, and should result in an error.
> {code}
> fil = filter l by a != null; -- This does not give an error, the correct
> usage is "a is not null"
> fil = filter l by a != adsf; -- this does give an error message saying that
> there is no column asdf
> {code}
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