Faulty response to certain queries combining DISTINCT and VALUES keywords #250
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Per Michael, This is likely to be a bug in the
ASTStaticBindingsOptimizer.
Bryan
…On Fri, Jun 28, 2024 at 03:58 simonrihm ***@***.***> wrote:
There seems to be a *bug* when parsing queries of the form
SELECT DISTINCT ?object WHERE { VALUES ?subject { <s1> <s2> } ?subject
<predicate> ?object .
Instead of returning all distinct objects related to the two given subject
instances by the predicate, it returns all instances of the subjects type.
This only happens when the following *conditions* are met:
a) Only the object is selected with DISTINCT keyword.
b) More than one instances are bound to the subject variable via VALUES
keyword.
c) Only one s-p-o statement is given as context.
*Workarounds* I have found so far:
1. Do not use DISTINCT keyword, instead add GROUP BY ?object at the
end of the query
2. Add a random second statement to the query that does not affect the
results, e.g. ?x ?y ?z .
You can *reproduce* this bug for example in Wikidata:
- Get fathers of Johann Sebstian Bach, Johann Jacob Bach, and Wolfgang
Amadeus Mozart: Works correctly as no DISTINCT keyword is used but returns
Johann Ambrosius Bach twice as he is the father of both Sebastian and Jacob
.
https://query.wikidata.org/#SELECT%20%3Ffather%0AWHERE%0A%7B%0A%20%20%3Fchild%20wdt%3AP22%20%3Ffather%20.%0A%20%20VALUES%20%3Fchild%20%7B%0A%20%20%20%20wd%3AQ1339%0A%20%20%20%20wd%3AQ539427%0A%20%20%20%20wd%3AQ254%0A%20%20%20%20%7D%0A%7D%0ALIMIT%2050
- Bug appears when DISTINCT keyword is added (LIIMIT therefore needed,
otherwise this tries to return every child on Wikidata):
https://query.wikidata.org/#SELECT%20DISTINCT%20%3Ffather%0AWHERE%0A%7B%0A%20%20%3Fchild%20wdt%3AP22%20%3Ffather%20.%0A%20%20VALUES%20%3Fchild%20%7B%0A%20%20%20%20wd%3AQ1339%0A%20%20%20%20wd%3AQ539427%0A%20%20%20%20wd%3AQ254%0A%20%20%20%20%7D%0A%7D%0ALIMIT%2050
- Use of Workaround 1:
https://query.wikidata.org/#SELECT%20%3Ffather%0AWHERE%0A%7B%0A%20%20%3Fchild%20wdt%3AP22%20%3Ffather%20.%0A%20%20VALUES%20%3Fchild%20%7B%0A%20%20%20%20wd%3AQ1339%0A%20%20%20%20wd%3AQ539427%0A%20%20%20%20wd%3AQ254%0A%20%20%20%20%7D%0A%7D%0AGROUP%20BY%20%3Ffather%0ALIMIT%2050
- Use of Workaround 2:
https://query.wikidata.org/#SELECT%20DISTINCT%20%3Ffather%0AWHERE%0A%7B%0A%20%20%3Fchild%20wdt%3AP22%20%3Ffather%20%3B%0A%20%20%20%20%20%20%20%20%20%3Fy%20%3Fz%20.%0A%20%20VALUES%20%3Fchild%20%7B%0A%20%20%20%20wd%3AQ1339%0A%20%20%20%20wd%3AQ539427%0A%20%20%20%20wd%3AQ254%0A%20%20%20%20%7D%0A%7D%0ALIMIT%2050
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There seems to be a bug when parsing queries of the form
SELECT DISTINCT ?object WHERE { VALUES ?subject { <s1> <s2> } ?subject <predicate> ?object .Instead of returning all distinct objects related to the two given subject instances by the predicate, it returns all instances of the subjects type. This only happens when the following conditions are met:
a) Only the object is selected with DISTINCT keyword.
b) More than one instances are bound to the subject variable via VALUES keyword.
c) Only one s-p-o statement is given as context.
Workarounds I have found so far:
GROUP BY ?objectat the end of the query?x ?y ?z .You can reproduce this bug for example in Wikidata:
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