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https://issues.apache.org/jira/browse/PIG-1788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13019916#comment-13019916
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Thejas M Nair commented on PIG-1788:
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Review of PIG-1788.patch -
- InvalidScalarProjectionException is used for several scalar errors, and the
reasons for those errors are not same as this one. So this same error message
is not applicable to all cases. I think the error message should be part of the
constructor of this exception so that the error message is correct.
- I think it makes sense to have a test case as well. Error messages are
important, and it is very easy to add test cases that test for error messages
such as this one. (for example see
TestProjectRange.testRangeCoGroupNegNoSchema() )
> relation-as-scalar error messages should indicate the field being used as
> scalar
> --------------------------------------------------------------------------------
>
> Key: PIG-1788
> URL: https://issues.apache.org/jira/browse/PIG-1788
> Project: Pig
> Issue Type: Bug
> Reporter: Thejas M Nair
> Assignee: Laukik Chitnis
> Fix For: 0.9.0
>
> Attachments: PIG-1788.patch
>
>
> Issue 1
> {code}
> grunt> l = load 'x' as (a,b,c);
> grunt> g = group l by a;
> grunt> f = foreach g generate COUNT(g); -- g is unintentionally being
> used as scalar , the user intends it to be COUNT(l) .
> 2011-01-05 12:44:53,098 [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR
> 1000: Error during parsing. Scalars can be only used with projections
> {code}
> Since the user did not intend to use a scalar, the scalar error messages are
> hard to understand.
> It will be useful to have the relation being used in scalar context in the
> error message. Something like - "ERROR 1000: Error during parsing. Relation g
> being used in scalar context at ... .Scalars can be only used with
> projections"
> Issue 2
> The error message "Scalars can be only used with projections" is not easy to
> understand. A better error message is needed, something like "A column needs
> to be projected from relation used in scalar context."
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