Re: Index not being used in MAX function (7.2.3)

> -----Original Message-----
> From: Dann Corbit
> Sent: Wednesday, June 11, 2003 10:12 AM
> To: Tom Lane; jim(at)nasby(dot)net
> Cc: pgsql-general(at)postgresql(dot)org
> Subject: Re: [GENERAL] Index not being used in MAX function (7.2.3)
>
>
> > -----Original Message-----
> > From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> > Sent: Wednesday, June 11, 2003 10:03 AM
> > To: jim(at)nasby(dot)net
> > Cc: pgsql-general(at)postgresql(dot)org
> > Subject: Re: [GENERAL] Index not being used in MAX function (7.2.3)
> >
> >
> > "Jim C. Nasby" <jim(at)nasby(dot)net> writes:
> > > Not to drag this out further, but you might want to hold
> > off on that
> > > patch. 7.4 is supposed to use indexes for max/min.
> >
> > Where did you get that idea?
> >
> > There's been no change in the basic problem, which is that no
> > one has proposed a reasonably general method of translating
> > aggregates into index manipulations. Postgres has an
> > extremely general, extensible concept of aggregates, and
> > we're not going to mess it up with some poorly-designed hack.
> > But show me a clean design and implementation, and it'll go in.
>
> Is this a poorly designed hack:
>
> Select max(expression) from <join> where <filter>
>
> Becomes:
>
> If (non_hashed_index_exists_on_expression) then
> /* Transform expression to: */
> select (expression) from <join> where <filter> order
> by <expression> limit to 1 rows

"Order by <expression> DESC" for max and ASC for min.

> else
> do_what_you_are_doing_right_now
> endif
> ?
>
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