I keep looking at this test, and while I understand the results given your conclusion, I'm not sure I understand how it would look differently if the order by happened before the return?
I like how the test doesn't depend on any natural document order so I'd like to understand it - I think it'll be handy to be able to write tests like this myself in future. -----Original Message----- From: Michael Blakeley <m...@blakeley.com> Reply-To: MarkLogic Developer Discussion <general@developer.marklogic.com> Date: Thursday, 2 October 2014 20:41 To: MarkLogic Developer Discussion <general@developer.marklogic.com> Subject: Re: [MarkLogic Dev General] order by clause ignored? I try not to rely on evaluation order anywhere, if I can help it. But I'm not sure whether MarkLogic's behavior matches the spec or not. According to http://www.w3.org/TR/xquery/#id-orderby-return "the resulting order determines the order in which the return clause is evaluated". I like tests, so here's one: for $i at $x in 1 to 5 let $_ := xdmp:sleep(1) let $start := xdmp:elapsed-time() order by $x descending return text { $x, $start, xdmp:elapsed-time() } => 5 PT0.006194S PT0.006221S 4 PT0.004826S PT0.004854S 3 PT0.003606S PT0.00364S 2 PT0.002314S PT0.002325S 1 PT0.001134S PT0.001211S With 7.0-4, the smallest elapsed-time values are at the end and both elapsed-time values match closely. To me this suggests that the return clause was evaluated before the results were sorted, not after. -- Mike On 2 Oct 2014, at 11:19 , Rachel Wilson <rachel.wil...@bbc.co.uk> wrote: > Thanks Mike, > > Are you saying never to do anything in the return statement that depends > on the order - that the order by clause only orders the final results. > It's so surprising because it does *mostly* work, until I added the >order > by clause it was *completely* wrong. And it's worked fine for other > simple data sets - just not against production data sadly :-) > > I think I've been lead astray in my expectations by the order by examples > for the return statement section in this article > http://www.stylusstudio.com/xquery_flwor.html > > Oh and a quick check - I'm assuming this is the same for any xquery > provider, it's not just a quirk of marklogic optimisation. > > Thanks for the lessons! > > Rachel > > -----Original Message----- > From: Michael Blakeley <m...@blakeley.com> > Reply-To: MarkLogic Developer Discussion ><general@developer.marklogic.com> > Date: Thursday, 2 October 2014 17:42 > To: MarkLogic Developer Discussion <general@developer.marklogic.com> > Subject: Re: [MarkLogic Dev General] order by clause ignored? > > The order of operations in a FLWOR isn't guaranteed. The return >expression > could be evaluated before the sorting is done. > > You might also be interested to know that maps are unordered. So you can > put those items into the map in any order you like, but the keys will end > up in whatever internal order the map uses. That should be consistent, >but > won't be under your control. > > As an alternative you can order the keys when processing the map. Or > consider using json:object instead. That's like a map but has an ordered > sequence of keys. > > -- Mike > > On 2 Oct 2014, at 09:17 , Rachel Wilson <rachel.wil...@bbc.co.uk> wrote: > >> I realise this is more of an xquery question but everyone here is >> stumped :-s >> >> I have a query that is trying to calculate some earliest and latest >> dates that an event occurred. The events are represented in xml like >> this: >> >> <publication> >> <publicationDateTime>2013-08-14T15:06:51.921302Z</publicationDateTime> >> <documents> >> <document> >> <id>b119c2a3-5436-59d2-9771-a67f8e2b4172</id> >> <version>1</version> >> </document> >> </documents> >> </publication> >> >> There are two events for the this particular document (i.e. with the >> same document id), and therefore two publication documents on different >> days. In order to work out the first and last dates I'm sorting all my >> publication docs by publication date, then taking the sorted publication >> documents in order I'm iterating through the publication document ids in >> order and remembering them in the correct maps for earliest seen and >> latest seen dates. However the results in the map are as if the >> publication documents are coming out in document order. >> >> If I run this query the document dates are coming out in the right order >> as I'd expect: >> ------------------------------------------------------------------ >> let $earliestPubDates := map:map() >> let $latestPubDates := map:map() >> let $buildMaps := >> for $x in doc()/publication >> let $publishedDate := $x/publicationDateTime/string() >> let $documents := $x/documents/document >> order by $x/publicationDateTime >> return >> (: map building stuff commented out in order to see how the dates >> are being ordered :) >> $publishedDate >> >> return $buildMaps >> --------------------------------------------------------------------- >> returns: >> 2013-08-14T15:06:51.921302Z >> 2014-09-03T14:46:07.757612Z >> >> >> >> However, after someone showed me how to debug the loop a little with an >> error statement, I'm finding that the first publication processed is the >> later one, not the earlier one. It looks like the order by in this case >> is being ignored. Could someone tell me how and why? >> >> >> >> >> >>------------------------------------------------------------------------- >>- >> -- >> let $earliestPubDates := map:map() >> let $latestPubDates := map:map() >> >> let $buildMaps := >> for $x in doc()/publication >> let $documents := $x/documents/document >> order by $x/publicationDateTime >> return >> for $contentId in $documents/id/string() >> let $publishedDate := $x/publicationDateTime/string() >> let $putEarliest := if (not(map:contains($earliestPubDates, >> $contentId))) then ( >> let $dummy := map:put($earliestPubDates, >> $contentId, $x/publicationDateTime) >> let $a := error("Adding earliest published >> date " || $x/publicationDateTime) >> return $dummy >> ) else () >> let $putLatest := map:put($latestPubDates, $contentId, >> $publishedDate) >> return () >> >> return $buildMaps >> ---------------------------------- >> Returns (in an error stack trace): "Adding earliest published date >> 2014-09-03T14:46:07.757612Z" >> >> >> Is it something to do with when the order by is applied to the >>statement? >> >> Any help gratefully received >> Rachel >> _______________________________________________ >> General mailing list >> General@developer.marklogic.com >> http://developer.marklogic.com/mailman/listinfo/general > > _______________________________________________ > General mailing list > General@developer.marklogic.com > http://developer.marklogic.com/mailman/listinfo/general > > _______________________________________________ > General mailing list > General@developer.marklogic.com > http://developer.marklogic.com/mailman/listinfo/general > _______________________________________________ General mailing list General@developer.marklogic.com http://developer.marklogic.com/mailman/listinfo/general _______________________________________________ General mailing list General@developer.marklogic.com http://developer.marklogic.com/mailman/listinfo/general
