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https://issues.apache.org/jira/browse/JENA-1468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16340940#comment-16340940
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Rick commented on JENA-1468:
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Thanks for looking into this Andy, it seems you've recreated the same issue
I've been driving at.
The "remaining issue" you mention is not a problem for us. We don't want the
VALUES block to be removed, and we want queries like this to evaluate to no
rows (as that's correct). The behaviour we currently get is the opposite.
i.e. when running through our whole stack is that we get all rows as the
binding is lost during printing.
> Empty VALUES clauses lose variable bindings when compiled to a SSE
> ------------------------------------------------------------------
>
> Key: JENA-1468
> URL: https://issues.apache.org/jira/browse/JENA-1468
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
> Affects Versions: Jena 3.1.1, Jena 3.2.0, Jena 3.3.0, Jena 3.4.0, Jena
> 3.5.0, Jena 3.6.0
> Reporter: Rick
> Priority: Major
> Labels: SPARQL, sse
>
> Given a SPARQL query like this:
> SELECT ?foo WHERE {
> ?foo ?bar ?baz . # Not essential for problem just to show we can't
> optimise it away.
> VALUES ?foo { }
> }
> If you compile it into an SSE with something like this:
> {{Algebra.compile(QueryFactory.create("SELECT ?foo WHERE \{ ?foo ?bar ?baz .
> VALUES ?foo { }}"));}}
> You end up with a semantically different SSE:
> {{(project (?foo)}}
> {{ (join}}
> {{ (bgp (triple ?foo ?bar ?baz))}}
> {{ (table empty)))}}
> Note how "(table empty)" has lost the ?foo binding, which means that this
> query returns all results for ?foo, where it should return no results.
> I'm not sure how this query should be expressed in SSE form I'd suggest:
> {{(table (vars ?foo) empty)}}
> Though currently this will get simplified in [code like
> this|https://github.com/apache/jena/blob/94eb3fc99ba1ff3991a629fffa6e6cf8b52d6c53/jena-arq/src/main/java/org/apache/jena/sparql/sse/builders/BuilderTable.java#L55-L64]
> into an EmptyTable if you do something like:
> {{BuilderTable.build(Item.createList((SSE.parse("(table (vars ?foo)
> empty)")));}}
> Additionally it appears quite a bit of code carries through this assumption
> that an [empty table will never have a
> binding|https://github.com/apache/jena/blob/94eb3fc99ba1ff3991a629fffa6e6cf8b52d6c53/jena-arq/src/main/java/org/apache/jena/sparql/algebra/table/TableEmpty.java#L57].
> As far as I can tell this issue effects many prior versions of JENA including
> 3.6.0.
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