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From:Gerald Clark Date:July 12 2002 1:37pm
Subject:Re: SELECT performance
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What would you expect?
You ask for the whole file, and then ask
that it be sorted by two fields.
How do you expect this to happen without  a temp file?

Tiago Antao wrote:

> Hi!
>
> I have a very simple query
> SELECT a, b FROM t ORDER BY a, b
> I also have an index on t(a)
> I have run ANALYZE
> Also the number of repetitions of values of a in t is very low.
>
> My view is that the execution should require little temporary space 
> and little time, something like:
> for each different a(already ordered and of fast access from index) {
>   get all rows (usually 3/4, max arround 300)
>   sort this (little) subset
> }
>
> What is happening is that a tmp file of the size of the t is being 
> generated.
>
> Is there any thing that I am not seeing? I there any way to change 
> this behaviour?
>
> Thanks,
> Tiago



Thread
SELECT performanceTiago Antao12 Jul
  • Re: SELECT performanceGerald Clark12 Jul