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https://issues.apache.org/jira/browse/HIVE-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844589#action_12844589
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Namit Jain commented on HIVE-1213:
----------------------------------
Consider the query;
select /*+ MAPJOIN(c) */ ...
from
(
select /*+ MAPJOIN(b) */ .. from a join b on k1
) subq
join
c
on k2
Even if k1 and k2 are not same, this can be done in a singe map-only job. Note
that this has nothing to do with sorting/bucketing etc.
> sort-merge join does not work for sub-queries
> ---------------------------------------------
>
> Key: HIVE-1213
> URL: https://issues.apache.org/jira/browse/HIVE-1213
> Project: Hadoop Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: Namit Jain
> Assignee: He Yongqiang
> Fix For: 0.6.0
>
> Attachments: Hive-1213.1.patch, Hive-1213.4.patch, Hive-1213.5.patch,
> Hive-1213.6.patch, Hive-1213.7.patch
>
>
> A query like:
> select count(1) from (select /*+ MAPJOIN(x) */ from x join y ON ... ) subq;
> does not work - since there is no mapping between the join operator and the
> corresponding source
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