what is the {start time} for {Frederick William, Elector of Brandenburg} has {spouse} as {Countess Louise Henriette of Nassau} ?
Frederick William, Elector of Brandenburg married Countess Louise Henriette of Nassus on which date?
When did Frederick William, Elector of Brandenburg marry Countess Louise Henriette of Nassau?
SELECT ?p WHERE { resource:Frederick_William property:spouse ?a . ?a property:spouse resource:Countess_Louise_Henriette_of_Nassau . ?a property:start_time ?p }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q152727> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P26> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q196301> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q152727 p:P26 ?s . ?s ps:P26 wd:Q196301 . ?s pq:P580 ?value}