[jira] [Commented] (JENA-1487) Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP BY
[
https://issues.apache.org/jira/browse/JENA-1487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=16397043#comment-16397043
]
Andy Seaborne commented on JENA-1487:
-
See JENA-1507.
> Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP
> BY
>
>
> Key: JENA-1487
> URL: https://issues.apache.org/jira/browse/JENA-1487
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
>Affects Versions: Jena 3.6.0
>Reporter: Claus Stadler
>Priority: Major
>
> Ordering an empty result set must not introduce additional bindings, but this
> happens with the following example (run on an arbitrary dataset - including
> an empty one):
> {code:bash}
> ./fuseki-server --file=test.ttl /foobar
> {code}
> The Json below is obtained from the Fuski bundle; but I noted this issue
> first using the ARQ API, where the incorrect result set contains a single
> BindingProjectNamed instance.
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> ORDER BY DESC(COUNT(?o))
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> {
> # NOTE THIS EMPTY BINDING HERE!
> }
> ]
> }
> }
> {code}
> The result set is correct without the ORDER BY:
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> # CORRECT
> ]
> }
> }
> {code}
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[jira] [Commented] (JENA-1487) Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP BY
[
https://issues.apache.org/jira/browse/JENA-1487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=16362205#comment-16362205
]
Andy Seaborne commented on JENA-1487:
-
This was discussed on the users mailing list in the past few months.
https://lists.apache.org/thread.html/72c2045e639c589880619443beafec5be963733e0f9f0887e134d467@%3Cusers.jena.apache.org%3E
The current behaviour in Jena is intended but it not clear, to me at least,
that is what the spec intended, or that the spec says. (The spec has some other
problems so it is not itself consistent.)
> Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP
> BY
>
>
> Key: JENA-1487
> URL: https://issues.apache.org/jira/browse/JENA-1487
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
>Affects Versions: Jena 3.6.0
>Reporter: Claus Stadler
>Priority: Major
>
> Ordering an empty result set must not introduce additional bindings, but this
> happens with the following example (run on an arbitrary dataset - including
> an empty one):
> {code:bash}
> ./fuseki-server --file=test.ttl /foobar
> {code}
> The Json below is obtained from the Fuski bundle; but I noted this issue
> first using the ARQ API, where the incorrect result set contains a single
> BindingProjectNamed instance.
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> ORDER BY DESC(COUNT(?o))
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> {
> # NOTE THIS EMPTY BINDING HERE!
> }
> ]
> }
> }
> {code}
> The result set is correct without the ORDER BY:
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> # CORRECT
> ]
> }
> }
> {code}
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[jira] [Commented] (JENA-1487) Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP BY
[
https://issues.apache.org/jira/browse/JENA-1487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel=16362080#comment-16362080
]
Rob Vesse commented on JENA-1487:
-
This behaviour is perfectly in line with the spec. The difference between the
two queries is the use of the {{COUNT(?o)}} aggregate. Per the specification
([https://www.w3.org/TR/sparql11-query/#defn_aggCount)] the count of a group is
the cardinality of the given variable which in this case is zero because the
cardinality of zero rows is always zero so using the aggregation introduces a
single binding.
Note that the fact that the aggregate occurs in the {{ORDER BY}} is not
relevant here, aggregates are extracted out and executed as part of the group
by operator per the specification
([https://www.w3.org/TR/sparql11-query/#sparqlGroupAggregate] and
[https://www.w3.org/TR/sparql11-query/#aggregateAlgebra]). This is more easily
seen in the algebra form:
{noformat}
(project (?s)
(order ((desc ?.0))
(group (?s) ((?.0 (count ?o)))
(sequence
(filter false
(table unit))
(bgp (triple ?s ?p ?o))
{noformat}
Versus:
{noformat}
(project (?s)
(group (?s)
(sequence
(filter false
(table unit))
(bgp (triple ?s ?p ?o)
{noformat}
Note that in the first form {{COUNT(?o)}} is converted into an expression as
part of the group operator so by the time that it is seen by {{ORDER BY}} it is
simply operating over a temporary internal variable.
> Incorrect SPARQL query result set when applying ORDER BY after an empty GROUP
> BY
>
>
> Key: JENA-1487
> URL: https://issues.apache.org/jira/browse/JENA-1487
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
>Affects Versions: Jena 3.6.0
>Reporter: Claus Stadler
>Priority: Major
>
> Ordering an empty result set must not introduce additional bindings, but this
> happens with the following example (run on an arbitrary dataset - including
> an empty one):
> {code:bash}
> ./fuseki-server --file=test.ttl /foobar
> {code}
> The Json below is obtained from the Fuski bundle; but I noted this issue
> first using the ARQ API, where the incorrect result set contains a single
> BindingProjectNamed instance.
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> ORDER BY DESC(COUNT(?o))
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> {
> # NOTE THIS EMPTY BINDING HERE!
> }
> ]
> }
> }
> {code}
> The result set is correct without the ORDER BY:
> {code:sql}
> SELECT ?s
> WHERE {
> ?s ?p ?o
> FILTER(false)
> }
> GROUP BY ?s
> {code}
> {code:json}
> {
> "head": {
> "vars": [ "s" ]
> } ,
> "results": {
> "bindings": [
> # CORRECT
> ]
> }
> }
> {code}
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