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https://issues.apache.org/jira/browse/HIVE-741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898756#action_12898756
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Ning Zhang commented on HIVE-741:
---------------------------------
@Amareshwar, currently we already distinguish different join types with
different functions (take a look at CommonJoinOperator.joinObjects()). I look
forward to seeing your proposal to avoid grouping null-keyed rows.
@Ted, I agree with Amareshwar and John that we cannot avoid rows (or the value
part of the key-value pairs) with null as a key. However you have a point in
that if we know the join operator does not involve outer join at all (we
already have a flag noOuterJoin in JoinDesc), then we could avoid sending rows
will null keys from the mappers to the reducers. This will save bandwidth as
well as processing time. Could you open another JIRA and be able to submit a
patch?
> NULL is not handled correctly in join
> -------------------------------------
>
> Key: HIVE-741
> URL: https://issues.apache.org/jira/browse/HIVE-741
> Project: Hadoop Hive
> Issue Type: Bug
> Reporter: Ning Zhang
> Assignee: Amareshwari Sriramadasu
>
> With the following data in table input4_cb:
> Key Value
> ------ --------
> NULL 325
> 18 NULL
> The following query:
> {code}
> select * from input4_cb a join input4_cb b on a.key = b.value;
> {code}
> returns the following result:
> NULL 325 18 NULL
> The correct result should be empty set.
> When 'null' is replaced by '' it works.
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