Re: Question on explain

Il 10/06/2013 04:19, Jeff Janes ha scritto:
> On further thought, that is not strange at all.  You have two very
> selective join conditions, and the planner assumes they are independent, so
> that it can multiply the selectivities.  But in reality they are completely
> (or almost completely) dependent.   If the planner knew about cross column
> correlations, that might not even help as you can have complete statistical
> dependence without having correlation.
>
> It seems unlikely to me that the timestamp belongs in both tables, since
> it's value seems to be completely dependent on the value of the UUID.
>
>
> In any event, it is unlikely the planner would pick a different plan were
> it to correctly understand the selectivities, so no harm is done.  Although
> it is easy to imagine similar queries where that would not be the case.
>
> Cheers,
>
> Jeff


Thank you very much ;)

Enrico

--
That's one small step for man; one giant leap for mankind

Enrico Pirozzi
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