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https://issues.apache.org/jira/browse/PIG-981?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Pradeep Kamath resolved PIG-981.
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Resolution: Duplicate
Fixed in
https://issues.apache.org/jira/browse/PIG-953?focusedCommentId=12761760&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12761760
> Merge join should restrict join key expressions to simple projects
> ------------------------------------------------------------------
>
> Key: PIG-981
> URL: https://issues.apache.org/jira/browse/PIG-981
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.4.0
> Reporter: Pradeep Kamath
> Assignee: Pradeep Kamath
>
> Currently merge join allows join key expressions to be arbitrary expressions
> with the assumption that the expressions keep the sort order. Since currently
> only ascending sort order is supported, the code checks at run times for sort
> order and catches the case where sort order is broken because the join key
> expression is not order preserving. However there is a reason we should
> restrict the join keys to projection of columns only:
> PIG-953 will enable pig to perform merge join to work with loaders and
> store functions which can internally index sorted data. These store functions
> can only create an index (and hence lookup on the index) on raw data columns
> (and not expressions on the columns).
> Hopefully this does not downgrade the usability of merge join much since if
> the expressions can always be applied post join on the join columns and since
> the expressions are order preserving they do not affect the outcome of the
> join.
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