Seonggon Namgung created HIVE-28488:
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Summary: Merge adjacent union distinct
Key: HIVE-28488
URL: https://issues.apache.org/jira/browse/HIVE-28488
Project: Hive
Issue Type: Improvement
Reporter: Seonggon Namgung
Assignee: Seonggon Namgung
Attachments: 1.MergeAdjacentUnionDistinct.pptx
Current Hive compiles
"SELECT * FROM TBL1 UNION SELECT * FROM TBL2 UNION SELECT * FROM TBL3"
to
{code:java}
TS - GBY - RS
TS - GBY - RS - GBY - RS
TS - GBY - RS - GBY {code}
This can be optimized as follows:
{code:java}
TS - GBY - RS
TS - GBY - RS
TS - GBY - RS - GBY {code}
Please check out the attached slides for detailed explanation and feel free to
ask any questions or share suggestions. Also, it would be glad if one can share
about better location of this optimization (e.g. SemanticAnalyzer, Calcite,
etc.).
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