Re: Order By for aggregate functions (Simulating Group_concat) - Mailing list pgsql-general

Michael Fuhr <mike@fuhr.org> writes:
> On Thu, Sep 01, 2005 at 05:14:41PM +0200, Martijn van Oosterhout wrote:
>> SELECT aggregate(field) FROM (SELECT field FROM xxx ORDER BY wherever) x;

> I've occasionally relied on this but I've never been completely
> comfortable with it.  Is there any guarantee that the subquery's
> ordering will be maintained as rows are fed to the aggregate, or
> is that just an accident of the current implementation?

Well, it's not required by the SQL spec (in fact I believe ORDER BY
inside a subselect isn't even legal per the SQL spec) ... but we do
promise it in the current implementation and I doubt we'd break the
promise in future, because it is a mighty handy behavior for
user-defined aggregates.

            regards, tom lane