query: #Unique value constraint report for P351: report listing each item
  SELECT DISTINCT ?item1 ?item1Label ?item2 ?item2Label ?value {	
    ?item1 wdt:P351 ?value .
    ?item2 wdt:P351 ?value .
    FILTER(?item1 != ?item2  && str(?item1)<str(?item2)) .
    SERVICE wikibase:label { bd:serviceParam wikibase:language "en,en" } .
  }