How many {time period} are to/by {Carboniferous} ?
Which is the number of time periods that there are in Carboniferous?
How many time period are Carboniferous?
SELECT ( COUNT ( ?g ) AS ?t ) { ?g property:time_period resource:Carboniferous }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P2348> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q133738 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P2348 wd:Q133738 }
20