query: #List of album contributions, order by contribution number
  SELECT DISTINCT ?contrib
  (GROUP_CONCAT(DISTINCT ?contribNr ; separator = " -- ") as ?ContributionNrs)
  ?contribLabel 
  
  WHERE {?contrib wdt:P31 wd:Q81564326;wdt:P361 wd:Q72752496 .  
          OPTIONAL{?contrib p:P1343 [ps:P1343 wd:Q82260552; pq:P958 ?contribNr].}
       
          SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }}
  GROUP BY  ?contrib ?contribLabel 
  ORDER BY ?ContributionNrs