----- "Ivan Mikhailov" <imikhai...@openlinksw.com> wrote:
> From: "Ivan Mikhailov" <imikhai...@openlinksw.com>
> To: "Peter Ansell" <p_ans...@yahoo.com>
> Cc: "Virtuoso Users List" <virtuoso-users@lists.sourceforge.net>
> Sent: Tuesday, 21 October, 2008 3:26:07 PM GMT +10:00 Brisbane
> Subject: Re: [Virtuoso-users] Aggregate queries using CONSTRUCT
>
> Hello Peter,
>
> First of all, there's a syntax error in construct pattern. Expressions
> should be backquoted when they appear in triple patterns as graphs,
> subjecs, predicates or objects. Construct pattern is a pattern, too, so
> it should be
>
> CONSTRUCT { <http://bio2rdf.org/interpro:IPR000181>
> <http://bio2rdf.org/ns/bio2rdf#hasLinkCount> `COUNT(?s)` . }
> WHERE { ?s ?p <http://bio2rdf.org/interpro:IPR000181> . }
>
> Next problem is that aggregates are not allowed to be direct arguments
> of aggregates, and CONSTRUCT is an aggregate by itself. One can't write
> COUNT(COUNT(x)), that is true for CONSTRUCT(...COUNT(...)) as well.
I wasn't aware that this was the reason it wasn't going to work, but thanks for
explaining it!
> I've tried the following workaround:
>
> CONSTRUCT { <http://bio2rdf.org/interpro:IPR000181>
> <http://bio2rdf.org/ns/bio2rdf#hasLinkCount> ?countS . }
> WHERE {
> { select (count(?s)) as ?countS
> where { ?s ?p <http://bio2rdf.org/interpro:IPR000181> . } } }
>
> That is a valid SPARQL and it is compiled to SQL that looks good for me.
> Unfortunately, SQL optimizer do not agree with me, because it realizes
> that I want to fool it.
>
> So the proper version is
>
> CONSTRUCT {
> <http://bio2rdf.org/interpro:IPR000181>
> <http://bio2rdf.org/ns/bio2rdf#hasLinkCount>
> `(select (count(?s)) as ?countS
> where { ?s ?p <http://bio2rdf.org/interpro:IPR000181> })` }
> where { ?s1 ?p1 ?o1 } limit 1
Just to check I understand... The real query is inside the CONSTRUCT and the
LIMIT 1 with ?s1 ?p1 ?o1 is just to ensure it returns results and is
syntactically valid SPARQL?
> Note backquotes _and_ parentheses around the scalar subquery. Backquotes
> are to delimit expression in pattern, parentheses are to delimit scalar
> subquery.
>
> Unfortunately, this query does not work on VOS versions earlier than
> 5.0.9-rc6 .
Thanks for looking into it! It is not time-critical at the moment to have this
query. I will put it into my package when I upgrade after 5.0.9 is released.
Cheers,
Peter
> Best Regards,
>
> Ivan Mikhailov,
> OpenLink Software
> http://virtuoso.openlinksw.com
>
> On Sun, 2008-10-19 at 23:20 -0700, Peter Ansell wrote:
> > Hi all,
> >
> > The documentation for the aggregation queries doesn't specifically
> say that it is only supported for SELECT queries [1] [2], but I have
> had no success in getting COUNT(?variable) to work inside of
> CONSTRUCT, where it works for a similar SELECT query. Any ideas about
> whether this is or will be supported in the future?
> >
> > For reference the two queries are as follows on
> http://quebec.bio2rdf.org/sparql
> >
> > SELECT COUNT(?s) WHERE { ?s ?p
> <http://bio2rdf.org/interpro:IPR000181> . }
> >
> > * http://tinyurl.com/5wrtcc
> >
> > CONSTRUCT { <http://bio2rdf.org/interpro:IPR000181>
> <http://bio2rdf.org/ns/bio2rdf#hasLinkCount> COUNT(?s) . } WHERE {
> ?s ?p <http://bio2rdf.org/interpro:IPR000181> . }
> >
> > * http://tinyurl.com/662vnh
> >
> > Cheers,
> >
> > Peter
> >
> > [1] http://docs.openlinksw.com/virtuoso/sparqlbi.html
> > [2] http://docs.openlinksw.com/virtuoso/rdfsparqlaggregate.html
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