Support COUNT() aggregation

[niklas88]

Aqqu generates queries using e.g. "SELECT COUNT(?var) WHERE .." to count (distinct?) entities. To port Aqqu to QLever the cleanest solution would be to support this. It should however also be possible to count client side in the specific use case in Aqqu.

[Buchhold]

I absolutely agree. A "clean" solution, however, should also add support for GROUP BY when starting with aggregates. I think this is very desirable. Maybe adding COUNT without GROUP BY is a good start, though. It should be extremely easy to add and would probably already help with everything Aqqu needs.

[niklas88]

Also Aqqu uses SELECT COUNT(?var0) WHERE {SELECT ?var0 ?var1 .. WHERE ..} like so

PREFIX fb: <http://rdf.freebase.com/ns/>
SELECT count(?1) WHERE {
SELECT ?1 WHERE {
 fb:m.01gbbz fb:award.award_nominee.award_nominations ?0 .
 ?0 fb:award.award_nomination.award_nominee ?1 .
 FILTER (?1 != fb:m.01gbbz) 
} LIMIT 30000}

[niklas88]

This has been implemented by now, thus closing