Re: [HACKERS] An optimisation question

Tom Lane wrote:
> 
> That's fixed for 6.6.  A workaround that partially solves the problem
> for 6.5 is to add a dummy WHERE clause referencing the ORDER-BY item:
>         select data from valori where data > '1/1/1800'
>         order by data limit 1;
> The WHERE is needed to get the 6.5 optimizer to consider the index
> at all.  In a quick test it seems this works for normal order but not
> DESC order... you could try applying the backwards-index patch that
> someone (Hiroshi or Tatsuo, I think) posted recently.

Yeap , I will search for it.

> There's no prospect of that happening anytime soon, I fear; there is no
> connection between aggregate functions and indexes in the system, and
> no easy way of making one.

Understand that, but.
Selects that deal ONLY with columns included in an index should operate
exclusively on that index and return the results. Example : select
sum(price) , price*1.2, max(price) from products , assuming that price
is included in an index it would be less cost to scan the index rather
than the whole table.

I remember that Paradox tables had  indexes and the index was also a
Paradox table or some sort of that. Internally it's possible that a
number of procedures related to tables could be applied to indexes. So,
a sum(price) from a_table could be easily switched to be done on any
index that contain the price field.

What do you think?

Constantin Teodorescu
FLEX Consulting BRaila, ROMANIA