How do I write a SPARQL query? [closed]

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How would I make a SPARQL query about rivers that flow into the Rhine, that are longer than 50 kilometers?

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Using DBpedia you could do something like this...

SELECT ?river ?riverName ?length
WHERE {
  ?river <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/Rhine> .
  ?river <http://dbpedia.org/ontology/length> ?length .
  FILTER (?length > 50000)
  ?river <http://www.w3.org/2000/01/rdf-schema#label> ?riverName .
  FILTER (lang(?riverName) = "en")
}
ORDER BY ?riverName

I'm assuming the length property in DBpedia uses meters, but you should check. You can test the query at http://dbpedia.org/sparql.

If this was homework and I just gave you the answer, I'd encourage you browse around at http://dbpedia.org/page/Rhine to see how I came up with it :)