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https://issues.apache.org/jira/browse/HIVE-20826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16680926#comment-16680926
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Ashutosh Chauhan commented on HIVE-20826:
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+1 Patch looks good. Can you also update RB with updated golden files too.
> Enhance HiveSemiJoin rule to convert join + group by on left side to Left
> Semi Join
> -----------------------------------------------------------------------------------
>
> Key: HIVE-20826
> URL: https://issues.apache.org/jira/browse/HIVE-20826
> Project: Hive
> Issue Type: Improvement
> Reporter: Vineet Garg
> Assignee: Vineet Garg
> Priority: Major
> Attachments: HIVE-20826.1.patch, HIVE-20826.2.patch,
> HIVE-20826.3.patch
>
>
> Currently HiveSemiJoin rule looks for pattern where group by is on right side.
> We can convert joins which have group by on left side (assuming group by keys
> are same as join keys and none of the columns are being projected from left
> side) to LEFT SEMI JOIN by swapping the inputs. e.g. queries such as:
> {code:sql}
> explain select pp.p_partkey from (select distinct p_name from part) p join
> part pp on pp.p_name = p.p_name;
> {code}
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