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Postgresql join

postgresql 中join的选项

  • Nested Loops(O(n2))

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    for x in table1:
      for y in table2:
        if x.field == y.field
          issue row
        else
          keep doing

  • Hash joins

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    Hash join
      Sequentialscan table 1
      Sequentialscan table 2

  • Merge joins(O(n * log(n)))

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    Merge join
      Sort table 1
        Sequetial scan table 1
      Sort table 2
        Sequetial scan table 2
    ---
    Merge join
      Index scan table 1
      Index scan table 2