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https://issues.apache.org/jira/browse/HIVE-28488?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17897924#comment-17897924
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Denys Kuzmenko commented on HIVE-28488:
---------------------------------------
Merged to master
Thanks [~seonggon], [~glapark] for the contribution, and [~okumin] for the
review!
> Merge adjacent union distinct
> -----------------------------
>
> Key: HIVE-28488
> URL: https://issues.apache.org/jira/browse/HIVE-28488
> Project: Hive
> Issue Type: New Feature
> Components: Logical Optimizer
> Reporter: Seonggon Namgung
> Assignee: Seonggon Namgung
> Priority: Major
> Labels: hive-4.1.0-must, pull-request-available
> Attachments: 1.MergeAdjacentUnionDistinct.pdf
>
>
> 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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