Greg Stark <gsstark@mit.edu> writes:
> "Bupp Phillips" <hello@noname.com> writes:
>> select * from customer order by customer_id, first_name;
>> [ where customer_id is the primary key ]
> However you do have a point. In this case I don't think postgres even
> considers using the index.
It will not, since the index does not appear to provide the correct sort
order.
> However I'm not sure I see a lot of cases where this would come up.
Yes, that's the real crux of the matter. Should the optimizer spend
cycles on *every* query to detect cases where the user has written
useless sort keys? I've got grave doubts that it's a win. ISTM such
an optimization penalizes the folk who write their queries well to
benefit those who are careless.
regards, tom lane