Re: weird behavior of ORDER BY

"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Thu, Apr 26, 2018 at 2:29 AM, zoolus . <700671@gmail.com> wrote:
>> I think any "ORDER BY" construct can't filter result set.

> ​While a bit surprising I don't really have a problem with it.  I suppose I
> would have expected that set-returning-functions in ORDER BY would be
> prohibited but absent that restriction this result is consistent with other
> behavior: if you had placed the unnest in the select-list and done "ORDER
> BY #" to reference it you would have achieved the same result.

Indeed.  Consider also the case where the SRF in ORDER BY produces more
than one output per input row --- how many result rows do you expect to
get then?  If you don't like reasoning about these cases, don't use a
SRF in ORDER BY.

            regards, tom lane