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https://issues.apache.org/jira/browse/PIG-927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12768027#action_12768027
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Daniel Dai commented on PIG-927:
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Hi, Alan,
Thank you for your comment. For the test case, if we do not have this patch, 
"1\t" for input1 will merge with "1\t" for input2, thus "join" will produce 2 
output records. With this patch, we can only see 1 output record.

> null should be handled consistently in Join
> -------------------------------------------
>
>                 Key: PIG-927
>                 URL: https://issues.apache.org/jira/browse/PIG-927
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.4.0
>            Reporter: Pradeep Kamath
>            Assignee: Daniel Dai
>             Fix For: 0.6.0
>
>         Attachments: PIG-927-1.patch, PIG-927-2.patch
>
>
> Currenlty Pig mostly follows SQL semantics for handling null. However there 
> are certain cases where pig may need to handle nulls correctly. One example 
> is the join - joins on single keys results in null keys not matching to 
> produce an output. However if the join is on >1 keys, in the key tuple, if 
> one of the values is null, it still matches with another key tuple which has 
> a null for that value. We need to decide the right semantics here. 

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