(select
 (leftjoin
  (join
   (bgp
     (triple ?:person |http://www.w3.org/1999/02/22-rdf-syntax-ns#|:type
             <http://xmlns.com/foaf/0.1/Person>)
     (triple ?:person <http://xmlns.com/foaf/0.1/name> ?:name))
   (graph ?:x
          (bgp
            (triple ?::?26 <http://xmlns.com/foaf/0.1/name> ?:name)
            (triple ?::?26 <http://xmlns.com/foaf/0.1/nick> ?:nick))))
  (union
   (bgp
     (triple ?:person <http://example.org/things#empId> ?:id))
   (bgp
     (triple ?:person <http://example.org/things#ssn> ?:ssn))))
 (?:id ?:ssn))