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From "Daniel Dai (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (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.
Date Fri, 01 May 2015 17:39:07 GMT

     [ https://issues.apache.org/jira/browse/PIG-2134?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Daniel Dai resolved PIG-2134.
-----------------------------
       Resolution: Duplicate
    Fix Version/s: 0.15.0
         Assignee: Niels Basjes

Mark it as duplicate. Thanks Niels!

> 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
>            Assignee: Niels Basjes
>            Priority: Minor
>              Labels: newbie
>             Fix For: 0.15.0
>
>
> (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 '.'? "



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