ARQ includes support for nested SELECTs.
This involves is syntactic extension and is available if the query is parsed
with language Syntax.syntaxARQ.
A SELECT query can be placed inside a graph pattern to produce a table that is used within the outer query. A nested SELECT statement is enclosed in {} and is the only element in that group.
Example: find toys with more than five orders:
PREFIX : <http://example/>
SELECT ?x
{
?x a :Toy .
{ SELECT ?x ( count(?order) as ?q ) { ?x :order ?order } GROUP BY ?x }
FILTER ( ?q > 5 )
}