Hi Jan,

Thanks for the reply. I tried as you suggested, but when I try the 'order by' clause with 'zero-or-one($s/timeOfDay)' or ''exactly-one($s/timeOfDay)', the query does compile and run, but without sorting the results.

I gather that these functions are checking if $s/timeOfDay contains zero-or-one and exactly-one item(s), respectively, and that they are returning nothing?, and so the order by clause does no ordering. However, this particular node that I wish to sort by (timeOfDay) contains no child nodes, only a single time and date string. My understanding is that by iterating through each of the 'stations' nodes using the nested for loop, the results should be ordered based on the 'timeOfDay' value of each 'stations' node.

Here's a snippet of the data for one 'stations' node:

<stations>
   <time>
       <hour>08</hour>
       <minute>34</minute>
       <second>50</second>
   </time>
   <timeOfDay>08:34:50 01-06-2010</timeOfDay>
   <timeUnit>milliseconds</timeUnit>
   <timeStart>1275377690000</timeStart>
   .....
   .....

Regards,
-Rob

On Sat, Mar 12, 2011 at 8:03 PM, Jan Rittinger <jan.rittinger@uni-tuebingen.de> wrote:

Hi Rob,

you can wrap '$s/timeOfDay' with a call to function 'zero-or-one()' or 'exactly-one()' (depending on what you know about your data). Then it will check at runtime (instead of at compile time) for the correctness of your query.

Regards,
Jan

On Mar 12, 2011, at 20:10, Rob Fynes wrote:

> Hello,
>
> I'm trying to produce a sorted list of results with MonetDB/XQuery using 'order by', with a query that goes something like this:
>
> for $cname in pf:collections()/text()
>   return
>     if (local:is-date-between($cname, **start_date_here**, **end_date_here**))
>     then
>       for $s in pf:collection($cname)//Dublin/stations[time/hour=13 and time/minute>=22 and time/minute<=25]
>       order by $s/timeOfDay
>       return $s
>     else ()
>
> ...the 'is-date-between' is just some custom function to check if the $cname (collection names are dates) is between the start and end dates supplied to the function.
> However, the problem is with the nested for loop. I want each $s that satisfies the XPath expression to be returned, but ordered by $s/timeOfDay.
>
> When I submit this query, I get the following error:
> ERROR = !type error: [err:XPTY0004] Orderspec requires at most one atomic item (given: string*).
>
> I've tried a number of variations on this, but the error is always the same.
> If I remove the order by clause, the results will return correctly, but in the unsorted order that they appear in the database.
>
> I'm still a beginner with XQuery, so I'm unsure where I'm going wrong, and documentation and tutorials have been unhelpful so far.
> Any help is appreciated!
>
> Regards,
> -Rob

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--
Jan Rittinger
Lehrstuhl Datenbanken und Informationssysteme
Wilhelm-Schickard-Institut für Informatik
Eberhard-Karls-Universität Tübingen

http://www-db.informatik.uni-tuebingen.de/team/rittinger


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