get highest number

[gonzberg at gmx.de]

Hello,
my question concerns a specific query. The query below retrieves about 100.000 results. Without ordering (line 2) the query takes 1 sec, with ordering it takes 40 secs. What I want to retrieve is the highest "id" in my data. What I do is retrieve all ids, order, retrieve the last "id". Is there a faster way to achieve this in XQuery?

let $y := for $x in //@id
order by number($x)
return $x
return xs:string($y[fn:last()])

Thanks for your help! gonzberg
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