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Issue with multiple OPTIONALs and COALESCE #1761

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aindlq opened this issue Feb 4, 2025 · 0 comments · May be fixed by #1847
Open

Issue with multiple OPTIONALs and COALESCE #1761

aindlq opened this issue Feb 4, 2025 · 0 comments · May be fixed by #1847

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@aindlq
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aindlq commented Feb 4, 2025

  1. If I have a query with multiple optionals where one of them produces no bindings, then the whole query produce no bindings.
PREFIX Platform: <http://www.researchspace.org/resource/system/>
PREFIX crm: <http://www.cidoc-crm.org/cidoc-crm/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

SELECT * WHERE {
  OPTIONAL {
    <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> crm:P67_refers_to ?refersToResourceConfig_1.
  }
  OPTIONAL {
    <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> rdf:type Platform:resource_configuration.
    BIND(<http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> AS ?refersToResourceConfig_2)
  }
  BIND(COALESCE(?refersToResourceConfig_1, ?refersToResourceConfig_2) AS ?resourceConfiguration)
}

query plan:

Image

If I remove first optional then the query actually produce results.

Can be reproduced with a single quad:

<http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.researchspace.org/resource/system/resource_configuration> <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> .
  1. I guess related issue with even simpler query, reproducible on any data. I have optional that produce no bindings and then want to use COALESCE to bind some variable to some default value.
PREFIX crm: <http://www.cidoc-crm.org/cidoc-crm/>

SELECT * WHERE {
  OPTIONAL {
    <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor> crm:P67_refers_to ?refersToResourceConfig_1.
  }
  BIND(COALESCE(?refersToResourceConfig_1, <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor>) AS ?resourceConfiguration)
}

If OPTIONAL is empty I would expect ?resourceConfiguration to be bound to <http://www.researchspace.org/resource/system/resource_configurations_container/data/Actor>.

Image
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Fix handling of OPTIONAL with empty or unconnected patterns RobinTF/qlever
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@aindlq