Hello,
How would one go about this one: I'm storing dateTime values for each
document.
I want to retrieve, efficiently, all unique dates (irrespective of the time
part) and the number of items with that date.
The naive implementation (because it takes about 1.5 seconds for not much
data):
let $c := collection("item")
return
for $d in distinct-values($c !
xs:date(xs:dateTime(.//normalized-dateTime/text())))
order by $d descending
return concat($d, " - ",
count($c//item[xs:date(xs:dateTime(.//normalized-dateTime)) = $d]))
The profiler tells me that it's spending about 85% of the time in the
predicate in the last line, so an index would probably speed up the lookups.
I created an element range index for the normalized-dateTime element, of
type dateTime. What I was hoping to be a bit less naive, turns out to be
not feasible:
for $d in distinct-values(collection("item")/item !
xs:date(xs:dateTime(./normalized-dateTime/text())))
order by $d descending
return concat($d, " - ",
count(
cts:search(/item,
cts:and-query((
cts:collection-query("item")
,
cts:element-range-query(xs:QName("normalized-dateTime"), "=", $d)
))
)
)
)
Now it complains that there is no element range index of type date for the
normalized-dateTime element, which is correct...
Would the recommendation be to add another element, normalized-date, that
contained only the date part and work with that, or is there possibly
another, even simpler solution?
cheers,
Jakob.
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