[jira] [Created] (HIVE-20826) Enhance HiveSemiJoin rule to convert join + group by on left side to Left Semi Join

["Vineet Garg (JIRA)" <ji...@apache.org>]

Vineet Garg created HIVE-20826:
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             Summary: 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


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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