Querying multiple graphs with aggregate Count and graph in results - sparql

Question

Is it possible to count the occurrences of triples in multiple named graphs and return the results as rows in a table? Such as:
?g ?count ?sequence_count
-------- ------- ---------------
graph1 54 54
graph2 120 80
Here is the query that I tried.
SELECT ?g ?count ?sequence_count
FROM NAMED <graph1>
FROM NAMED <graph2>
WHERE {
{
select (COUNT(?identifier) as ?count) (COUNT(?sequence) as ?sequence_count)
WHERE { GRAPH ?g {
?identifier a <http://www.w3.org/2000/01/rdf-schema#Resource> .
OPTIONAL { ?identifier <urn:sequence> ?sequence }
} }
}
}
But the results were:
?g ?count ?sequence_count
-------- ------- ---------------
174 134
I'm trying to avoid having to write out:
select ?count_graph1 ?sequence_count_graph1 ?count_graph2 ...
as there could be hundreds of graphs to query.

Answer 1

First, the query is really close. Just move the SELECT inside of the graph statement - basically stating 'for each graph, find these aggregate values'. Second, if any of the ?identifier matches have multiple values, the count for ?identifier will have duplicates, so DISTINCT results are necessary. Try the following:
SELECT *
FROM NAMED <graph1>
FROM NAMED <graph2>
WHERE {
GRAPH ?g {
SELECT (COUNT(DISTINCT ?identifier) as ?count) (COUNT(?sequence) as ?sequence_count)
WHERE {
?identifier a <http://www.w3.org/2000/01/rdf-schema#Resource> .
OPTIONAL { ?identifier <urn:sequence> ?sequence }
}
}
}