Potential problem with GROUP BY in RDF::Query when using RDF::Trine::Store::Memory

[minusdavid]

Using RDF::Query, I have a SPARQL query that has a GROUP BY, but it doesn't seem to be working with RDF::Trine::Store::Memory.

Still need to investigate more...

[minusdavid]

In my logs I see:

SELECT ?subject
WHERE {
?subject ?predicate ?object .
FILTER NOT EXISTS { ?os ?op ?subject }
}
GROUP BY ?subject

Become:

using query plan: (project (subject) (filter (! (sparql:exists (BGP
(triple ?os ?op ?subject)

[kasei]

You're on a roll finding issues. Really sorry about that! This does seem like a big, but I'll mention that this is a strange query that might be more naturally expressed as "select distinct ?subject" without any grouping. That said, using grouping without any aggregate functions like SUM should still work and I'll try to get a fix for that.

[minusdavid]

I'm nearly finished with my RDF code, so I probably won't be finding many more soon!

Great suggestion. I changed it to use 'select distinct' instead and that works a treat. Sounds good about getting a fix out though. I always use 'GROUP BY' with SQL rather than 'DISTINCT', so I hadn't even thought to use it here with SPARQL.