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  1. Hive
  2. HIVE-28488

Merge adjacent union distinct

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    Description

      Current Hive compiles
      "SELECT * FROM TBL1 UNION SELECT * FROM TBL2 UNION SELECT * FROM TBL3"
      to

      TS - GBY - RS
TS - GBY - RS - GBY - RS
           TS - GBY - RS - GBY

      This can be optimized as follows:

      TS - GBY - RS
TS - GBY - RS
TS - GBY - RS - GBY

      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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        1. 1.MergeAdjacentUnionDistinct.pdf
          595 kB
          Seonggon Namgung

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            seonggon Seonggon Namgung
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