Hi,
Forget the last one. I've just realized again I included a mistake....
this is the good one (I hope ;))
# Case 1)
select ?id ?value ?latitude ?longitude
where {
......
}
----------
{
"head": {
"vars": [
"id", "value", "latitude", "longitude"
]
},
"results": {
"bindings": [
]
}
}
# Case 2)
select ?id (MAX(?ti) as ?time) ?value ?latitude ?longitude
where {
......
}
----------
{
"head": {
"vars": [
"id", "time", "value", "latitude", "longitude"
]
},
"results": {
"bindings": [
{}
]
}
}
Now you can see the difference I was noticing. In the first case
bindings is an empty array (resultset.hasNext() -> false) and the second
is an array with an empty object (resultset.hasNext() -> true).
Why is this behaviour? Hope you now understand the issue which in my
opinion is a kind of a bug.
Regards,
Jorge
On 2017-10-08 00:15, George News wrote:
> Hi Andy,
>
> Now I understand the misunderstanding between you and me. The responses
> I included in my original mail where wrong :( Please accept my apologizes.
>
> These are the right query/responses:
>
> # Case 1)
> select ?id (MAX(?ti) as ?time) ?value ?latitude ?longitude
> where {
> ......
> }----------
> {
> "head": {
> "vars": [
> "id", "time", "value", "latitude", "longitude"
> ]
> },
> "results": {
> "bindings": [
> {}
> ]
> }
> }
>
> # Case 2)
> select ?id (MAX(?ti) as ?time) ?value ?latitude ?longitude
> where {
> ......
> }----------
> {
> "head": {
> "vars": [
> "id", "value", "latitude", "longitude"
> ]
> },
> "results": {
> "bindings": [
> ]
> }
> }
>
> Now you can see the difference I was noticing. In the first case it is
> an empty array (resultset.hasNext() -> false) and the second is an array
> with an empty object (resultset.hasNext() -> true).
>
> Why is this behaviour? Hope you now understand the issue which in my
> opinion is a kind of a bug.
>
> Regards,
> Jorge
>
>
>
>
>
> On 2017-10-06 16:11, Andy Seaborne wrote:
>>
>>
>> On 06/10/17 12:26, George News wrote:
>>> 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).
>>
>> "results": {
>> "bindings": [
>> {}
>> ]
>> }
>>
>> both times.
>>
>> An array of rows, a row is {} i.e. no keys, no variables.
>>
>> But the query isn't legal so I don't know what is actually happening.
>>
>>>
>>>>
>>>> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>
>
