use another sparql inside sparql IN clause

Question

I'm using SPARQL and I wonder if I can put an sparql inside in clause? To be more specific, I need to get entities(s1,s2) who have specific condition for this sparql query[s1's aggregate value over a field is more than say 5]

select 
?s1 ?x ?s2.
WHERE {
         {?s1 rdf:type dbpedia-owl:Scientist.}
         {?s2 rdf:type dbpedia-owl:Scientist.}
         {?s2 dbpedia-owl:field ?x.}
         {?s1 dbpedia-owl:field ?x.}
}

so I need to add an extra IN clause like this

SELECT
?s1 ?x ?s2.
WHERE {
      {?s1 rdf:type dbpedia-owl:Scientist.}
      {?s2 rdf:type dbpedia-owl:Scientist.}
      {?s2 dbpedia-owl:field ?x.}
      {?s1 dbpedia-owl:field ?x.}
      {?s1 IN 
            {
             SELECT  ?s1  WHERE {
                                    SELECT ?s1 (COUNT(?p) AS ?prizes) {
                                    ?s1 dbpprop:prizes ?p.
                                    } group by (?s1) 
                                 }FILTER (?prizes > 2) 
             }
       }
 }

But I got error on the sparql query parser..... does anybody know how to fix it?

Answer 1

IN has a somewhat different usage in SPARQL than SQL, it can only be used within a FILTER like so:

FILTER(?s IN (<this>, <that>, <another>))

However just using the sub-query on it's own should give you the desired result because of the bottom up join semantics of SPARQL evaluation:

SELECT ?s1 ?x ?s2
WHERE 
{
  ?s1 rdf:type dbpedia-owl:Scientist.
  ?s2 rdf:type dbpedia-owl:Scientist.
  ?s2 dbpedia-owl:field ?x.
  ?s1 dbpedia-owl:field ?x.
  {
    SELECT ?s1 WHERE 
    {      
      ?s1 dbpprop:prizes ?p.
    }
    GROUP BY ?s1 
    HAVING (COUNT(?p) > 2) 
  }
}

You may notice I simplified some other parts of your query as well. There is no need to use two nested sub-queries because you can specify an aggregate condition using the HAVING clause.

Also you do not need to put { } around each individual triple pattern and in fact doing so may significantly harm performance.

Answer 2

As per official W3C documentation,

IN

boolean  rdfTerm IN (expression, ...)

The IN operator tests whether the RDF term on the left-hand side is found in the values of list of expressions on the right-hand side. The test is done with "=" operator, which tests for the same value, as determined by the operator mapping.

A list of zero terms on the right-hand side is legal.

Errors in comparisons cause the IN expression to raise an error if the RDF term being tested is not found elsewhere in the list of terms.

The IN operator is equivalent to the SPARQL expression:

(lhs = expression1) || (lhs = expression2) || ...

Examples:

So, IN operator accepts list of vales, where as when we use a nested SPARQL query using select operator (As shown in your example), it returns Resultset, you can think of like list of statements. Hence you can not do it in that way.

However below is an example, you can try with as per SPARQL FILTER +IN syntax:

SELECT
?s1 ?x ?s2.
WHERE {
      {?s1 rdf:type dbpedia-owl:Scientist.}
      {?s2 rdf:type dbpedia-owl:Scientist.}
      {?s2 dbpedia-owl:field ?x.}
      {?s1 dbpedia-owl:field ?x.}
      FILTER (?s1 IN (<http://example.com/#1>,<http://example.com/#2>, <http://example.com/#3>)) 
 }