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https://issues.apache.org/jira/browse/JENA-1468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16342139#comment-16342139
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ASF GitHub Bot commented on JENA-1468:
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GitHub user afs opened a pull request:
https://github.com/apache/jena/pull/345
JENA-1468: Retain variables in op (table)
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/afs/jena empty-table
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/jena/pull/345.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #345
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commit 30eb9314a4076c6adc06b348556650297b2b9283
Author: Andy Seaborne <andy@...>
Date: 2018-01-26T13:53:05Z
JENA-1468: Writing vars when table empty
commit 2586abf09751fd962ca7afe25d4ab3d9431ce716
Author: Andy Seaborne <andy@...>
Date: 2018-01-26T13:53:17Z
JENA-1468: Tests
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> 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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