Wikidata Query misses results - sparql

Question

I am trying to query all the countries from Wikidata (query link):
SELECT ?item WHERE { ?item wdt:P31 wd:Q6256. }
Unfortunately, the results are missing for example Switzerland (Q39):
https://www.wikidata.org/wiki/Q39
Looking at the Switzerland data, it has the triple: instance of (P31) country (Q6256).
Could you help me understand why Q39 is not present in the results then?
Thanks!

Answer 1

In WikiData, often you have what are called statements. These allow for qualifications to those statements.
For instance, in the case of Switzerland being a country, the qualification is that the rank of this statement should be 'normal' instead of preferred.
The preferred way to refer to Switzerland is sovereign state (wd:Q3624078), and it looks like WikiData will only have a wdt:P31 relationship between an entity and its 'preferred rank' classification only, as this query shows.
I think this could be because 'country' is a more generic concept, e.g. Wales is a country but not a sovereign state.
Fear not however, as this query:
SELECT DISTINCT ?item
WHERE {
?item p:P31/ps:P31 wd:Q6256.
}
returns wd:Q39 as well. What this query is doing is to navigate from Switzerland to Country via the statement.
That is, we have in our data:
wd:Q39 p:P31 wds:Q39-fbe1ac75-4a8a-93c4-6009-81055d79f9cb .
wds:Q39-fbe1ac75-4a8a-93c4-6009-81055d79f9cb ps:P31 wd:Q6256 .
but not:
wd:Q39 wdt:P31 wd:Q6256 .
Try this:
SELECT DISTINCT *
WHERE {
?item p:P31 ?y .
?y ps:P31 wd:Q6256 ;
?p ?o .
VALUES ?item {wd:Q39}
}
to see for yourself.