[jira] [Commented] (JENA-1507) GROUP BY and aggregates when there are no matching of the WHERE pattern.

["Andy Seaborne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-1507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16397081#comment-16397081 ] 

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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