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https://issues.apache.org/jira/browse/HIVE-16797?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Pengcheng Xiong reassigned HIVE-16797:
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> Support a new rule RemoveUnionBranchRule
> ----------------------------------------
>
> Key: HIVE-16797
> URL: https://issues.apache.org/jira/browse/HIVE-16797
> Project: Hive
> Issue Type: Bug
> Reporter: Pengcheng Xiong
> Assignee: Pengcheng Xiong
>
> in query4.q, we can see that it creates a CTE with union all of 3 branches.
> Then it is going to do a 3 way self-join of the CTE with predicates. The
> predicates actually specifies only one of the branch in CTE to participate in
> the join. Thus, in some cases, e.g.,
> {code}
> /- filter(false) -----TS0
> union all - filter(false) -----TS1
> \-----TS2
> {code}
> we can cut the branches of TS0 and TS1. The union becomes only TS2.
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