| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Thiago Godoi <thiagogodoi10(at)gmail(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Intersect/Union X AND/OR |
| Date: | 2011-12-02 19:49:42 |
| Message-ID: | 201112021949.pB2Jng821759@momjian.us |
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| Thread: | |
| Lists: | pgsql-performance |
Thiago Godoi wrote:
> Hi all,
>
> I found this presentation from B. Momjian:
>
> http://momjian.us/main/writings/pgsql/performance.pdf
>
> I'm interested in what he said about " Intersect/Union X AND/OR " , Can I
> find a transcription or a video of this presentation? Can anyone explain it
> to me?
Well, there is a recording of the webcast on the EnterpriseDB web site,
but I am afraid they only allow viewing of 3+ hour webcasts by
EnterpriseDB customers.
The idea is that a query that uses an OR can be rewritten as two SELECTs
with a UNION between them. I have seen rare cases where this is a win,
so I mentioned it in that talk. Intersection is similarly possible for
AND in WHERE clauses.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
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