Re: EOAndQualifier order
Re: EOAndQualifier order
- Subject: Re: EOAndQualifier order
- From: Miguel Arroz <email@hidden>
- Date: Thu, 12 Jul 2007 11:19:05 +0100
Hi!
PostgreSQL manual, chapter 11, the section about multi-column
indexes. I realized, after further testing, that the planner tries to
re-arrange the order. But I think there are situations where the
planner may choose one or another column because there's no "optimum"
solution, and that choice comes from the order of the args. But I'm
not sure about any os this, I don't know a lot about DBs, and I hate
them more everyday.
Yours
Miguel Arroz
On 2007/07/12, at 01:08, Q wrote:
On 12/07/2007, at 7:29 AM, Miguel Arroz wrote:
Hi!
I'm looking and the generated SQL from an EOAndQualifier, and it
looks like the order of the "anded" stuff is the inverse one I
write on the code. If I write a qualifier like "bananas = %@ and
apples = %@ and oranges = %@", the generated SQL will be the
reverse (t0.oranges = (...) AND t0.apples = (...) AND to.bananas =
(...)".
Is this normal? Is the order random? What's happening here? I'm
asking this, because from what I understand form the PostgreSQL
docs, the order of the stuff in ANDs (and ORs) may have cause a
really big difference in performance when indexes (and multi-
indexes) are envolved.
Where exactly did you read this? Order of the conditional
expressions shouldn't make any difference to the query planner.
--
Seeya...Q
Quinton Dolan - email@hidden
Gold Coast, QLD, Australia (GMT+10)
Ph: +61 419 729 806
Miguel Arroz
http://www.terminalapp.net
http://www.ipragma.com
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