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