[jira] [Commented] (PIG-2134) ReadScalars message "scalar has more than one row in the output" does not provide enough information to help programmer find and fix script syntax error.

["Daniel Granatshtein (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PIG-2134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586363#comment-13586363 ] 

Daniel Granatshtein commented on PIG-2134:
------------------------------------------

Thanks for posting and the details on this issue! 
Searched for the error and hit this open ticket. Seeing the resolution, I imagine it would have taken some time to resolve myself. 
                
> ReadScalars message "scalar has more than one row in the output" does not provide enough information to help programmer find and fix script syntax error.
> ---------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: PIG-2134
>                 URL: https://issues.apache.org/jira/browse/PIG-2134
>             Project: Pig
>          Issue Type: Improvement
>          Components: impl
>    Affects Versions: 0.8.0, 0.9.0
>            Reporter: Michael Brauwerman
>            Priority: Minor
>
> (Bug filed on 0.8. I do not have 0.9 to test.)
> This applies to org.apache.pig.impl.builtin.ReadScalars.java:83
> http://search-hadoop.com/c/Pig:/src/org/apache/pig/impl/builtin/ReadScalars.java
> I have bitten myself with the same programming error several times, and each time I spent too long diagnosing my error.
> The error message "scalar has more than one row in the output" is a bit misleading, considering the underlying programming mistake.
> Consider this Pig script:
> A = LOAD 'a' as (key, a1, a_junk);
> B = LOAD 'b' as (key, b1, b_junk);
> C = join A by key, B by key;
> -- Now, we want to project (key, a1, b1)
> -- CORRECT:
> D_GOOD = foreach C generate A::key, a1, b1;  -- Disambiguate 'key' correctly.
> -- Now, consider some common programmer errors:
> -- INCORRECT:
> -- This fails, because 'key' is ambiguous. The error message is clear enough.
> D_BAD_1 = foreach C generate key, a1, b1;  
> -- This fails whenever A has multiple rows.
> D_BAD_2 = foreach C generate A.key, a1, b1
> -- Error: "Scalar has more than one row in the output 1st : t1, 2nd : t2"
> That's non-illuminating, for the following reason:
> The error message is assuming that the programmer is making a semantic error, trying to use a value from the original A, which is impossible if A has more than one row. 
> In actuality, the programmer wants A::key, but he made a syntax error by typing "A.key", and it resulted in "scalar has more than one row" message that has nothing to do with what he intended. 
> Since he has confused "." and "::", he has no context for interpreting the message properly.
> Ideally, the error message would say something like this:
>  "A.key cannot be used as scalar here, because A has more than one row. Did you mean A::key?"
> If the identifiers are not available at error-logging time, something like this would be helpful:
>  "Relation cannot be used as scalar here, because A has more than one row. Did you mean to use '::' instead of '.'? "

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira