Joshua Taylor created JENA-633:
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Summary: subqueries with limits project more results than they
should
Key: JENA-633
URL: https://issues.apache.org/jira/browse/JENA-633
Project: Apache Jena
Issue Type: Bug
Components: ARQ, Jena
Affects Versions: Jena 2.11.0
Reporter: Joshua Taylor
A subquery with `limit 1` specified can `leak` more values to the surrounding
query. Rob Vesse tracked this down to a difference between the basic algebra
and the optimized algebra [1] . One query has the following basic and
optimized Ops; the "join" in the former shouldn't get turned into a "sequence"
in the latter.
Basic:
(join
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<urn:ex:Thing>))
(slice _ 1
(project (?resource ?p)
(order (?p)
(bgp (triple ?resource <urn:ex:p> ?p))))))
Optimized:
(sequence
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<urn:ex:Thing>))
(project (?resource ?p)
(top (1 ?p)
(bgp (triple ?resource <urn:ex:p> ?p)))))
[1]
http://answers.semanticweb.com/questions/26343/outer-query-results-include-more-values-than-subquery-with-limit-n-produces/26344
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