query: # members of the 1837-41 Parliament -658 seats.
  SELECT DISTINCT ?constituency ?constituencyLabel ?typeLabel ?start ?end ?item ?itemLabel
  {
   ?item p:P39 ?positionStatement .
   ?positionStatement ps:P39 wd:Q41582550 . 
   ?positionStatement pq:P768 ?constituency . 
   OPTIONAL { ?constituency wdt:P31 ?type . }
   OPTIONAL { ?constituency wdt:P571 ?start . }
   OPTIONAL { ?constituency wdt:P576 ?end . }
   SERVICE wikibase:label { bd:serviceParam wikibase:language 'en' }
  }