Run selected subquery returns zero rows

Stardog Studio
1

Easy to recreate - try selecting and running this subquery:

# 12-albums-dates-subselect.sparql
prefix : <http://stardog.com/tutorial/>

SELECT (avg(?count) AS ?avgCount)
{
      SELECT ?year (count(?album) AS ?count)
      {
            ?album a :Album ;
                  :date ?date ;
            BIND (year(?date) AS ?year)
      }
      GROUP BY ?year
}

returns no rows - because of the lack of default prefix

However when you run this subquery it works:

# 12-albums-dates-subselect.sparql
prefix : <http://stardog.com/tutorial/>

SELECT (avg(?count) AS ?avgCount)
{
      prefix : <http://stardog.com/tutorial/>
      SELECT ?year (count(?album) AS ?count)
      {
            ?album a :Album ;
                  :date ?date ;
            BIND (year(?date) AS ?year)
      }
      GROUP BY ?year
}