Re: Intersect/Union X AND/OR

On Fri, Dec 2, 2011 at 1:49 PM, Bruce Momjian <bruce@momjian.us> wrote:
> 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.

I've seen this as well.  Also boolean set EXCEPT is useful as well in
the occasional oddball case.

merlin