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

pá 1. 2. 2019 v 19:03 odesílatel PG Bug reporting form <
noreply(at)postgresql(dot)org> napsal:

> The following bug has been logged on the website:
>
> Bug reference: 15618
> Logged by: cd a
> Email address: cdalxndr(at)yahoo(dot)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