On 09/10/17 15:27, George News wrote:
On 2017-10-09 12:31, james anderson wrote:
good afternoon;
On 2017-10-09, at 12:03, George News <[email protected]> wrote:
On 2017-10-09 11:53, Lorenz Buehmann wrote:
On 09.10.2017 10:22, George News wrote:
Hi all,
Here it goes. The MWE is below.
As you can see when I execute Q_without.rq I get an empty array in
bindings. However with Qmax_without.rq I get {} (empty object) in
bindings.
What I'm saying is that if I'm getting nothing when listing the
matching entities, I don't know why I get an empty object when
listing the matching entities with an aggregate operation like MAX.
Well, I guess Andy already gave you the answer in the beginning of
the thread: A query with an aggregate always returns a row by
convention. But compared to the aggregate function COUNT which simply
can return 0 then, MAX can't return any concrete value because the
MAX of nothing is not specified.
I understood it, but I don't agree with this behaviour. Is this in the
standard or is it just Jena behaviour?
the recommendation describes the intended behaviour here :
https://www.w3.org/TR/sparql11-query/#aggregateAlgebra
I guess this is it. If the standard says so, we have to stick to it,
although not in favour of that solution.
I haven't convinced myself that Jena is right (I haven't checked -
virtuos seemed to do the same though which isn't proof but it's a
completed unconnected implementation) and even if it is, whether the
spec is saying what it means to say. I don't see different cases for
COUNT(*) and AnyAgg(?x) because I'd expect them to be different in the
case of no GROUP BY.
The presence of GROUP BY fundamentally changes the nature of the query.
Does anybody knows a way to avoid loading the whole resultset in memory
to check if it has one row and then rewind it to the beginning?
ASK WHERE { pattern }
Andy
Thanks.
best regards, from berlin,
---
james anderson | [email protected] | http://dydra.com
