| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | George Pavlov <gpavlov(at)mynewplace(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: huge disparities in =/IN/BETWEEN performance |
| Date: | 2007-02-09 02:14:14 |
| Message-ID: | 20070209021414.GU24069@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-sql |
George Pavlov wrote:
> the basic question i have is fairly clear though: why saying "where x =
> 10" should be different (in ANY cicumstance, not just mine) from saying
> "where x between 10 and 10" or from "where x in (select ... /* some
> query that returns 10 */)" ???
I think the principle here is that the system is not gonna waste cycles
on dumb queries. Supposedly, morphing "foo BETWEEN 10 and 10" into
"foo=10" is not a trivial transformation, and it'd impose a planning
cost on all non-dumb BETWEEN queries. That cost is best avoided: if you
optimize for dumb users, the smart users then want you buried because
you've lost performance doing useless work.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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