Hello list,
INITIAL REMARK: if this is not the appropriate mailing list for this
question, please let me know the best place to ask questions regarding
SPARQL queries and their optimization.
I'm a beginner when it comes to writing SPARQL queries. I am trying to
speed up a certain query that I got from someone, which has the
following form:
SELECT ?val (COUNT(DISTINCT ?id) as ?vc)
WHERE
{
?id <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?val.
?id ?property ?property_value.
?property_value bif:contains "'foo'".
?id ?property1 ?property_value1.
?property_value1 bif:contains "'bar'".
}
GROUP BY ?val
ORDER BY DESC(?vc)
First of all, I noticed that I can write it more elegantly as follows:
SELECT ?val (COUNT(DISTINCT ?id) as ?vc)
WHERE
{
?id <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?val ;
?property1 ?property_value1 ;
?property2 ?property_value2 .
?property_value1 bif:contains "'foo'" .
?property_value2 bif:contains "'bar'" .
}
GROUP BY ?val
ORDER BY DESC(?vc)
Secondly, looking at
http://docs.openlinksw.com/virtuoso/queryingftcols.html my educated
guess was that I could replace this query with
SELECT ?val (COUNT(DISTINCT ?id) as ?vc)
WHERE
{
?id <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?val ;
?property ?property_value .
?property_value bif:contains 'foo or bar' .
}
GROUP BY ?val
ORDER BY DESC(?vc)
and my hope was that this version would run a little faster (don't ask
me why... just a wild guess that I would try)
Unfortunately, this last version seems to give different query results.
My two questions:
1) Why is this last query giving different results? Am I
misinterpreting something?
2) Is there a way I can rewrite the original query so that it runs faster?
Thanks!
Bart
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