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https://issues.apache.org/jira/browse/JENA-1010?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14702754#comment-14702754
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Andy Seaborne commented on JENA-1010:
-------------------------------------
{{?.0}} is an internally generated variable used to assign the value of
{{(count ?o)}} -- this is than assigned to {{?c}} and {{?.0}} is invisible.
{{(group (?prop) ((?.0 (count ?o)))}} is calculate the group and aggregate
count into ?.0.
There are various times internal variables are generated - they are always
synactically illegal names to avoid clashes with any used in the query. You
can see {{?/x}} sometimes, even {{?//x}}.
{{(extend)}} is the algebra operator for {{BIND}}.
It is done via a temporary because
{noformat}
SELECT (count(*) AS ?c1) (count(*) AS ?c2) { .... }
{noformat}
or
{noformat}
SELECT (count(*) AS ?c1) { ... }
HAVING (count(*) > 2)
{noformat}
still only calculates {{count(*)}} once.
You see {{(filter (> ?.0 1)}} because the {{HAVING}} has no {{AS}}.
> Wrong parsing of aggregate functions in HAVING clause
> -----------------------------------------------------
>
> Key: JENA-1010
> URL: https://issues.apache.org/jira/browse/JENA-1010
> Project: Apache Jena
> Issue Type: Bug
> Components: Jena
> Affects Versions: Jena 2.13.0
> Reporter: Ruben Navarro Piris
> Assignee: Andy Seaborne
> Fix For: Jena 3.0.0
>
>
> Using an aggregate funtion (count) in the HAVING clause leads to some weird
> parsing. The following code reproduces the problem (output also provided)
> {code:java}
> public class Test {
> public static void main(String[] args) {
> AlgebraGenerator ag = new AlgebraGenerator();
> // this query counts the number of occurrences of a property
> // showing only properties with more than one occurrence
> String q =
> "SELECT (count(?o) AS ?c) ?prop "
> + "WHERE { GRAPH ?g { ?s ?prop ?o } } "
> + "GROUP BY ?prop HAVING ( count(?o) > 1 ) "
> + "ORDER BY DESC(?c) ?prop";
> Query query = QueryFactory.create(q);
> System.out.println(query);
> Op queryOp = ag.compile(query);
> System.out.println(queryOp);
>
> Query rewritten = OpAsQuery.asQuery(queryOp);
> System.out.println(rewritten);
> }
> }
> {code}
> {code}
> SELECT (COUNT(?o) AS ?c) ?prop
> WHERE
> { GRAPH ?g
> { ?s ?prop ?o}
> }
> GROUP BY ?prop
> HAVING ( COUNT(?o) > 1 )
> ORDER BY DESC(?c) ?prop
> (project (?c ?prop)
> (order ((desc ?c) ?prop)
> (filter (> ?.0 1)
> (extend ((?c ?.0))
> (group (?prop) ((?.0 (count ?o)))
> (graph ?g
> (bgp (triple ?s ?prop ?o))))))))
> SELECT ?c ?prop
> WHERE
> { { GRAPH ?g
> { ?s ?prop ?o}
> BIND(COUNT(?o) AS ?c)
> }
> FILTER ( ?.0 > 1 )
> }
> GROUP BY ?prop
> ORDER BY DESC(?c) ?prop
> {code}
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