On Fri, 16 Jul 2004 12:04:54 -0400, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>	select sum(x), sum(y), sum(x)-sum(y) from ...
>
>At least since 7.4, the system will notice the duplicate aggregates
>and run only two summations to compute the above, followed by a single
>subtraction at the end.  The apparently more intelligent way suggested
>by Jean will have to run three summations, and thus end up being a net
>loss.

Also note that Jean-Luc's
	select sum( x), sum( y), sum(x-y) from whatever group by z;
gives a different result in the presence of NULLs.

Servus
 Manfred

In response to

• Re: Column as result of subtraction of two other columns? at 2004-07-16 16:04:54 from Tom Lane

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