How to write an inquiry flwor xquery? - xpath

Question

I have 5 cars, each car with 5 owners, I need to return those owners whose nation does not appear in the owners of other cars (can appear in the owners of the same car):
<root>
<car>
<id>1</id>
<owner>
<name>George Smith</name>
<nation>USA</nation>
</owner>
<owner>
<name>Carolina Herre</name>
<nation>USA</nation>
</owner>
<owner>
<name>Martha Belar</name>
<nation>Denmark</nation>
</owner>
<owner>
<name>Fernando Izza</name>
<nation>Italy</nation>
</owner>
<owner>
<name>George Smith</name>
<nation>Italy</nation>
</owner>
</car>
<car>
<id>2</id>
<owner>
<name>George Gelar</name>
<nation>USA</nation>
</owner>
<owner>
<name>Gema Bio</name>
<nation>Spain</nation>
</owner>
<owner>
<name>Peter Vdf</name>
<nation>Denmark</nation>
</owner>
<owner>
<name>Felipe Rodriguez</name>
<nation>Denmark</nation>
</owner>
<owner>
<name>George Smith</name>
<nation>USA</nation>
</owner>
</car>
<car>
...
</car>
<car>
...
</car>
<car>
...
</car>
</root>
That is, given that xml, the output would be:
<owner>
<name>Fernando Izza</name>
<nation>Italy</nation>
<carID>1</carID>
</owner>
<owner>
<name>George Smith</name>
<nation>Italy</nation>
<carID>1</carID>
</owner>
<owner>
<name>Gema Bio</name>
<nation>Spain</nation>
<carID>2</carID>
</owner>
I tried to get the list of countries that do not appear in several cars, and then get those owners who are from those countries, but I do not know how to get it.

Answer 1

You can just group the owners by their nation and then look upwards to see if the nation occurs below more than one car:
for $owner in doc("cars.xml")//car/owner
group by $nation := $owner/nation
where count($owner/..) eq 1
for $o in $owner
return <owner>{
$o/*,
<carID>{$o/../id/text()}</carID>
}</owner>