Re: [GENERAL] Perfomance of IN-clause with many elements and possible solutions

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От David G. Johnston
Тема Re: [GENERAL] Perfomance of IN-clause with many elements and possible solutions
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Msg-id CAKFQuwaHP_ZzCQZVdt-6DrjV0WHaSaYJDoDCNX-nf3NNXGUtHQ@mail.gmail.com
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Ответ на Re: [GENERAL] Perfomance of IN-clause with many elements and possiblesolutions  (Dmitry Lazurkin <dilaz03@gmail.com>)
Ответы Re: [GENERAL] Perfomance of IN-clause with many elements and possiblesolutions
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On Mon, Jul 24, 2017 at 3:12 PM, Dmitry Lazurkin <dilaz03@gmail.com> wrote:
And I have one question. I don't understand why IN-VALUES doesn't use Semi-Join? PostgreSQL has Hash Semi-Join...  For which task the database has node of this type?

​Semi-Join is canonically written as:

SELECT *
FROM tbl
WHERE EXISTS (SELECT 1 FROM tbl2 WHERE tbl.id = tbl2.id)

The main difference between IN and EXISTS is NULL semantics.

David J.

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