jena-arq/testing/ARQ/Expr1/expr-2.rq

PREFIX  dc: <http://purl.org/dc/elements/1.1/>
PREFIX  x: <http://example.org/ns#>
SELECT  ?title ?price
WHERE
    { ?book dc:title ?title . 
      OPTIONAL
        { ?book x:price ?price } . 
      FILTER (?price < 15)  .
    }