How to filter for a condition with two columns? - sparql

Question

For a course I follow I have to write several SPARQL queries about Lego sets. I am interested in finding out if there is a Lego theme which has a single package type.
I have the following SPARQL query:
select distinct ?theme ?package_type (count(?theme) as ?amount_of_lego_sets)
where{
?Lego_set rdf:type wd:Q58780257 .
?Lego_set sch:audienceType ?audience .
?Lego_set ex:has_package_information ?package_info .
?audience ex:belongs_to_theme ?theme .
?package_info ex:has_packaging_type ?package_type .
} group by ?theme ?package_type
order by ?theme
Which produces the following output:
As you can see there is one set that has the theme “4 Juniors” and the package type “Polybag”. Now, I am interested in themes like Advanced models or Action Wheelers which only have a single package type. However, I found it challenging to filter for these themes.
What modification to my query could I implement to remove themes which have sets that have more than one package type?

Answer 1

This is an interesting question. I would use FILTER NOT EXISTS to add an atom to the query body, where we make sure that the theme doesn't have two types of packages, like this:
FILTER NOT EXISTS {
?Lego_set2 sch:audienceType ?audience2 .
?Lego_set2 ex:has_package_information ?package_info2 .
#Notice that the 'theme' variable must be the same as the outer query
?audience2 ex:belongs_to_theme ?theme .
?package_info2 ex:has_packaging_type ?package_type1, ?package_type2
FILTER(?pakage_type1 != ?package_type2)}
Thus your full query should be something like:
select distinct ?theme ?package_type (count(?theme) as ?amount_of_lego_sets)
where{
?Lego_set rdf:type wd:Q58780257 .
?Lego_set sch:audienceType ?audience .
?Lego_set ex:has_package_information ?package_info .
?audience ex:belongs_to_theme ?theme .
?package_info ex:has_packaging_type ?package_type .
FILTER NOT EXISTS {
?Lego_set2 sch:audienceType ?audience2 .
?Lego_set2 ex:has_package_information ?package_info2 .
#Notice that the 'theme' variable must be the same as the outer query
?audience2 ex:belongs_to_theme ?theme .
?package_info2 ex:has_packaging_type ?package_type1, ?package_type2
FILTER(?pakage_type1 != ?package_type2)}
} group by ?theme ?package_type
order by ?theme
You could also use the aggregation approach mentioned in the comments, but hopefully this one solves your problem.