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https://issues.apache.org/jira/browse/HIVE-20826?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Vineet Garg updated HIVE-20826:
-------------------------------
    Status: Open  (was: Patch Available)

> 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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