Re: Passing distinct subquery solutions to aggregate outer query

On Jan 24, 2013, at 8:45, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:

> Joining the evaluation of {} with X yields X, not a single solution of null bindings.

Yes, I just learned that reading further in the spec. Now it is more of a puzzle. I will try to work up a simple example to replicate the problem.

> 
> Is it a typo that:
> 
> [[
> select distinct ?var1 ?var ?var3
> ]]

Yes, typo. The select variables are identical in inner and outer queries.

Thanks,
--Paul
> 
> has ?var not ?var2
> 
>    Andy
> 
> 
> On 24/01/13 14:31, Paul Tyson wrote:
>> 
>> Lee,
>> 
>> 
>> On Jan 24, 2013, at 0:36, Lee Feigenbaum <lee@thefigtrees.net
>> <mailto:lee@thefigtrees.net>> wrote:
>> 
>>> Hi Paul,
>>> 
>>> Why would the outer query need any graph patterns other than the
>>> subquery? You ought to be able to do exactly what you have below
>>> without anything in the "what goes here" spot.
>>> 
>> That's what I thought at first, but it returns a single solution with no
>> bindings. After studying the spec (SPARQL 1.1 section 12) I see this is
>> probably as specified, because it joins the solution projected from the
>> inner query to the solution from the outer query. The empty outer graph
>> pattern returns a single solution of null bindings (per spec 5.2.1).
>> 
>> Regards,
>> --Paul
>> 
>>> Lee
>>> 
>>> On 1/23/2013 3:56 PM, Paul Tyson wrote:
>>>> Hi all,
>>>> 
>>>> I'm wondering if there is a simple solution to this problem.
>>>> 
>>>> I have a rather complicated query, consisting of several union
>>>> clauses, which by its nature will return duplicates. I need to get a
>>>> unique solution set so I can group them and sum a couple of fields.
>>>> 
>>>> Simply wrapping the union query in a nested SELECT DISTINCT doesn't
>>>> work, because the outer query has no graph pattern to match the
>>>> variables projected from the subquery.
>>>> 
>>>> I tried adding a series of BIND statements to simply rename the
>>>> subquery variables for use by the aggregate outer query, but that
>>>> didn't work (with jena, at least).
>>>> 
>>>> The source dataset is nearly 500M triples. I'm using Jena 2.7.3. The
>>>> subquery will return anywhere from a few dozen to a few hundred
>>>> solutions, and by itself runs very quickly.
>>>> 
>>>> Here's a skeleton view of the query. Is there something to fill "what
>>>> goes here" that will pass the subquery results up to the grouping
>>>> function?
>>>> 
>>>> select ?var1 ?var2 (sum(?var3) as ?var3_total)
>>>> where {
>>>> { ??? what goes here ??? }
>>>> {select distinct ?var1 ?var ?var3
>>>> where { ... complicated union query ... }}
>>>> }
>>>> group by ?var1 ?var2
>>>> 
>>>> Or any other suggestions on how to tackle this problem?
>>>> 
>>>> Thanks,
>>>> --Paul
>>>> 
>>>> 
>>> 
>

Received on Thursday, 24 January 2013 15:22:32 UTC