Re: optimising UNION performance

[Rafal Pietrak <rafal(at)zorro(dot)isa-geek(dot)com>]

This is a little strange - my response to this post apparently got lost
in the net?? I haven't received it back through the list nor it's
visible in the archieve. Yet, my exim logfile contains entry indicating
'delivery complited'???

But to the point.

All the EXPLAIN ANALISE I did on posggres v8.1.4 - plain *.deb binary
install from debian network repository.

So if version v8.1 was expected to behave any differently, it doesn't.
But may be the reduction improvement are in some pre-8.2 versions?

-R

On Mon, 2006-08-28 at 10:46 -0400, Tom Lane wrote:
> Alban Hertroys <alban(at)magproductions(dot)nl> writes:
> > There's practically no difference between SELECT 1 FROM ... and SELECT * 
> > FROM ...; the only added costs (AFAIK) are for actually fetching the 
> > column values and such. Pretty cheap operations.
> 
> You're both glossing over exactly the wrong thing, particularly seeing
> that Rafal appears to be using 8.0 or older which hasn't got 8.1's
> significant reductions in targetlist evaluation costs.
> 
> 			regards, tom lane
> 
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-R