[JENA-2342] SPARQL query comparing "count(distinct ?v)" values is evaluated incorrectly

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Jena 4.5.0
• Fix Version/s: Jena 4.6.0
• Component/s: SPARQL
• Assignee: Andy Seaborne
• Reporter: Jakub Galgonek
• Created: 05/Aug/22 12:04
• Updated: 25/Aug/22 09:43
• Resolved: 09/Aug/22 12:02

Description

I encountered the following issue while testing the neXtProt database in Jena.

If the query –

select ?id where {
  values (?id ?v1 ?v2) { ('A' 'B' 'C') }
} group by ?id having (count(distinct ?v1) = count(distinct ?v2))

– is submitted, then the empty result is returned. However, the result –

( ?id = "A" )

– should by returned.

On the other hand, the query –

select ?id where {
  {select ?id (count(distinct ?v1) as ?c1) (count(distinct ?v2) as ?c2) {
    values (?id ?v1 ?v2) { ('A' 'B' 'C') }
  } group by ?id}
  filter (?c1 = ?c2)
}

– returns the result as expected.

The following code can be used to reproduce the issue:

import org.apache.jena.query.QueryExecution;
import org.apache.jena.query.QueryExecutionFactory;
import org.apache.jena.query.ResultSet;
import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.ModelFactory;

public class Test {
  static String query1 = "select ?id where { values (?id ?v1 ?v2) { ('A' 'B' 'C') } } group by ?id having (count(distinct ?v1) = count(distinct ?v2))";
  static String query2 = "select ?id where { {select ?id (count(distinct ?v1) as ?c1) (count(distinct ?v2) as ?c2) { values (?id ?v1 ?v2) { ('A' 'B' 'C') } } group by ?id} filter (?c1 = ?c2) }";

  public static void main(String[] args) {
    evaluate("Query1:", query1);
    evaluate("Query2:", query2);
  }

  public static void evaluate(String name, String query) {
    Model model = ModelFactory.createDefaultModel();
    QueryExecution qexec = QueryExecutionFactory.create(query, model);
    ResultSet results = qexec.execSelect();

    System.out.println(name);
    while(results.hasNext())
      System.out.println(results.nextSolution());
  }
}

Issue Links

• links to: GitHub Pull Request #1471