How many teams have used the stadium which hosted the WCW mayhem?
SELECT DISTINCT COUNT(?uri) WHERE { <http://dbpedia.org/resource/WCW_Mayhem> <http://dbpedia.org/property/venue> ?x . ?x <http://dbpedia.org/ontology/tenant> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Stadium>}
WCW_Mayhem