Re: optimizer question

> Bruce Momjian wrote:
> >
> > > "Reinoud van Leeuwen" <reinoud(at)xs4all(dot)nl> writes:
> > > > I have a table that contains almost 8 milion rows. The primary key is a
> > > > sequence, so the index should have a good distribution. Why does the
> > > > optimizer refuse to use the index for getting the maximum value?
> > >
> > > The optimizer has no idea that max() has anything to do with indexes.
> > > You could try something like
> > >
> > > select * from tab order by foo desc limit 1;
> >
> > Can we consider doing this optimization automatically?
>
> Only if we assume that people do not define their own max() that does
> something
> that can't be calculated using the above formula like calculating AVG().

I hadn't thought of that one. I can't imagine a max() that doesn't
match the ORDER BY collating.

Updated TODO item:

* Use indexes for min() and max() or convert to SELECT col FROM tab
ORDER BY col DESC LIMIT 1;

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