On 2017-10-06 11:25, Andy Seaborne wrote:
> The two result sets you show both have one row, with bindings. That's
> consistent with aggregation of nothing (no groups, or if no GROUP BY, no
> results from the WHERE pattern.
I don't see it the same way. The first one (without max) is an empty
array, while the second (with max) has an array with one object (empty).
>
> MAX() of nothing is unbound but for any aggregation, there always is a row/
>
> c.f. COUNT(*) is 0 when there are no solution.
>
> It's just MAX(...) can't return a "there isn't anything value"
>
> Andy
>
I see your point as this gives a wrong idea on the result set as it
really is empty. If I dont get any time I cannot calculate the max of
nothing. In principle this is what Jena is returning as the object is
empty, but there should be a way to not get this empty object within the
array of bindings.
Is there anyway I can check the resultset pointer to get the next()
value without moving the pointer? I need to know in advance to retrieve
all the results if there are or aren't any.
>
> On 06/10/17 10:15, George News wrote:
>> Hi all,
>>
>> I am executing a SPARQL with MAX aggregate function and I'm facing a
>> strange behaviour, or at least I think it is.
>>
>> The snipset of the select variables is the following:
>>
>> select ?id (MAX(?ti) as ?time) ?value ?latitude ?longitude
>> where {
>> ......
>> }
>
>>
>> If I launch the SPARQL query and there are results matching there is no
>> problem and I get the expected answer.
>>
>> However if I launch the same query over another database and there
>> should be no match I get the following:
>>
>> {
>> "head": {
>> "vars": [
>> "id", "time", "value", "latitude", "longitude"
>> ]
>> },
>> "results": {
>> "bindings": [
>> {}
>> ]
>> }
>> }
>>
>> As you can see, although the resultset seems to be empty it is not. It
>> is returning one empty object. Actually by checking resultset.hasNext()
>> within the code it returns true.
>>
>> If I remove the MAX function from the variables everything is ok, and no
>> empty object shows up.
>>
>> select ?id ?value ?latitude ?longitude
>> where {
>> ......
>> }
>> ----------
>> {
>> "head": {
>> "vars": [
>> "id", "value", "latitude", "longitude"
>> ]
>> },
>> "results": {
>> "bindings": [
>> {}
>> ]
>> }
>> }
>>
>> Why is happening that? Is this the expected behaviour? I guess it
>> shouldn't. When you use COUNT funtion it returns 0, but MIN/MAX/etc arer
>> different functions and if there is no result nothing should appear.
>>
>> Any help/tip is more than welcome.
>>
>> Regards,
>> Jorge
>>
>>
>>
>>
>>
>
