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https://issues.apache.org/jira/browse/PIG-4724?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14988012#comment-14988012
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Prashant Kommireddi commented on PIG-4724:
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[~rohini] what are your thoughts on this? I'm not sure if this breaks the way
users expect output to be based on the current behavior, but sounds like the
right thing to do?
cc [~daijy]
> GROUP ALL must create an output record in case there is no input
> ----------------------------------------------------------------
>
> Key: PIG-4724
> URL: https://issues.apache.org/jira/browse/PIG-4724
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.15.0
> Reporter: Prashant Kommireddi
>
> {code}
> A = load 'data';
> B = filter A by $0 == 'THIS_DOES_NOT_EXIST';
> C = group B ALL;
> D = foreach C generate group, COUNT(B);
> {code}
> Even if the filter did not output any rows, since we are grouping on ALL the
> expected output should probably be (ALL, 0). The implementation generates a
> pseudo key “all” for every input on map side, thus reduce side we can combine
> all input together. However, this does not work for 0 input since the reduce
> side does not get any input. If the input is empty, yield a pseudo “all, 0”
> to reduce
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