Michael Fuhr <mike@fuhr.org> writes:
> On Mon, Mar 21, 2005 at 07:20:04PM +0000, Peter Cottingham wrote:
>> Appears that the GROUP BY clause is not working correctly on new server
>> (GROUP BY should order the result set in ASCENDING order, NOT DESCENDING
>> order.) See below
> As far as I know, the SQL standards don't specify that GROUP BY is
> supposed to give a particular order.
> Somebody please correct me if I'm mistaken
You're not. Peter is apparently accustomed to databases that only know
how to implement GROUP BY with a sort-and-uniq kind of implementation
... that would include Postgres from a few years ago ... but there is
no such requirement in the spec.
Current PG versions are likely to implement GROUP BY with a hashing
method, which will yield a completely unsorted output. It is pure
coincidence that it happened to look like descending order in Peter's
example.
regards, tom lane