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https://issues.apache.org/jira/browse/PIG-4541?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dipankar updated PIG-4541:
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Summary: Skewed full outer join does not return records if any relation is
empty. Outer join does not return any record if left relation is empty (was:
Skewed full outer join does not return records if any relation is empty. )
> Skewed full outer join does not return records if any relation is empty.
> Outer join does not return any record if left relation is empty
> ----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: PIG-4541
> URL: https://issues.apache.org/jira/browse/PIG-4541
> Project: Pig
> Issue Type: Bug
> Components: build
> Affects Versions: 0.14.0
> Environment: HDP 2.2.4
> Reporter: Dipankar
>
> Test1:
> Perform full join on two relation with left relation being blank and right
> containing records
> empty_relation = FILTER a_relation by (join_column=='eliminate everything');
> Test_output = JOIN empty_relation by (join_column) FULL , non_empty_relation
> by (join_column);
> Result : Zero records returned.
> Test2:
> Perform full join on two relation with left relation being blank and right
> containing records using skewed
> Test_output = JOIN empty_relation by (join_column) FULL , non_empty_relation
> by (join_column) using ‘skewed’;
> Result : Zero records returned.
> Test3:
> Perform full join on two relation with left relation being blank and right
> containing records using parallel
> Test_output = JOIN empty_relation by (join_column) FULL , non_empty_relation
> by (join_column) PARALLEL 10;
> Result : Zero records returned.
> Test4:
> Perform full join on two relation with left relation being non empty and
> right not containing records using parallel
> Test_output = JOIN , non_empty_relation by (join_column) FULL ,
> empty_relation by (join_column) PARALLEL 10;
> Result : valid records returned.
> Observation:
> 1) If the either relation is blank , skewed full outer join does not return
> anything
> 2) If the non empty relation is kept on left, everything works except skewed
> 3) FULL OUTER will only work if the left relation is not empty
> 4) Skewed will only work if both relation is non empty.
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