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https://issues.apache.org/jira/browse/JENA-1507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16397081#comment-16397081
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Andy Seaborne commented on JENA-1507:
-------------------------------------
The SPARQL spec is wrong as well:
In the definition of "Group",
[https://www.w3.org/TR/sparql11-query/#defn_algGroup]
If the pattern does not match, Ω is empty and so "Group(exprlist, Ω)" is the
empty set ∅ because it says at the end "| μ in Ω }"; Ω is empty so there is
for-each evaluation.
Once "Group(exprlist, Ω)" is the empty set, it is identical to "GROUP BY" and
no match, ending up in no rows.
But, for example, COUNT(*) is supposed to be 0 in the single row. There is
always a single row when there is no GROUP BY, even if it is a row of no
columns (no aggregate functions). (It is not possible to write that in SPARQL
- an aggregate is needed to trigger being all-one-group).
> GROUP BY and aggregates when there are no matching of the WHERE pattern.
> ------------------------------------------------------------------------
>
> Key: JENA-1507
> URL: https://issues.apache.org/jira/browse/JENA-1507
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
> Affects Versions: Jena 3.6.0
> Reporter: Andy Seaborne
> Assignee: Andy Seaborne
> Priority: Major
>
> There are two bugs in ARQs handling of grouping when there are no results in
> the WHERE clause.
> When there is a GROUP BY, the outcome should be no rows.
> * JENA-1487
> * [users list
> discussion|https://lists.apache.org/thread.html/72c2045e639c589880619443beafec5be963733e0f9f0887e134d467@%3Cusers.jena.apache.org%3E]
> When there is no GROUP BY, no aggregates, and no pattern match, the result
> should be one row of no columns; when there is no GROUP BY, the result is
> always one row. It returns zero rows (v3.6.0 and before).
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