Pradeep Kamath resolved PIG-981.

    Resolution: Duplicate

Fixed in 

> 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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