rdf

Apparently sparql doesn't allow non aggregate variables in the select clause unless they are also in the group by, which affects the query's meaning. So I came up with another solution which includes an intersection(join):

select ?country ?area ?lake
where {
?lake rdfs:label ?label .
?lake rdf:type dbo:Lake .
?lake dbo:areaTotal ?area .
?lake dbo:country ?country .
?country rdf:type dbo:Country .
FILTER (lang(?label) = 'en') .
FILTER(?maxarea = ?area)
{
select ?country (MAX(?area) AS ?maxarea)
where {
?lake rdfs:label ?label .
?lake rdf:type dbo:Lake .
?lake dbo:areaTotal ?area .
?lake dbo:country ?country .
?country rdf:type dbo:Country .
FILTER (lang(?label) = 'en') .
}
group by ?country
}
}