(select
 (join
  (bgp
    (triple <http://example/x> <http://example/p> ?:v))
  (leftjoin
   (bgp
     (triple <http://example/x> <http://example/q> ?:w))
   (bgp
     (triple <http://example/x> <http://example/p> ?:v2))
   :TEST (= ?:v 1)))
 (?:v ?:w ?:v2))