Re: BUG #15618: Duplicating a join clause breaks index use

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От Pavel Stehule
Тема Re: BUG #15618: Duplicating a join clause breaks index use
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Msg-id CAFj8pRAFqKsQcyLfrzm2NAfuEvDMk8mV+6TsxF5UrhGKgv2opg@mail.gmail.com
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Ответ на BUG #15618: Duplicating a join clause breaks index use  (PG Bug reporting form <noreply@postgresql.org>)
Ответы Re: BUG #15618: Duplicating a join clause breaks index use
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pá 1. 2. 2019 v 19:03 odesílatel PG Bug reporting form <noreply@postgresql.org> napsal:
The following bug has been logged on the website:

Bug reference:      15618
Logged by:          cd a
Email address:      cdalxndr@yahoo.com
PostgreSQL version: 10.3
Operating system:   Windows 10
Description:       

Adding a unused join clause to the query, modifies the run time from 50ms to
4seconds.
No columns from the join clause are returned and the joined table is not
used in other places.
The join clause is a duplicate of another one that is used for further
joining.

The joined clause should have been automatically removed as it has no side
effects, thus using indices and optimizing query runtime.

Please, can you send a example. Generally, you can remove only some outer join clauses. unused inner join cannot be removed, because it can has impact on result.

Regards

Pavel Stehule

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