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https://issues.apache.org/jira/browse/JENA-1526?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andy Seaborne updated JENA-1526:
--------------------------------
    Issue Type: Question  (was: Bug)

> OPTIONAL clause filters out results when defined before inner SELECT
> --------------------------------------------------------------------
>
>                 Key: JENA-1526
>                 URL: https://issues.apache.org/jira/browse/JENA-1526
>             Project: Apache Jena
>          Issue Type: Question
>         Environment: apache-jena-fuseki-3.7.0
>            Reporter: Kevin Smyth
>            Priority: Major
>
> Given this dataset
> {code:java}
> @prefix ns1: <http://example.com/ns1#> .
> @prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
> <ns1://Example#R1>
> a ns1:type_ ;
> ns1:sb <http://example.com/#Mass_29> .
> <http://example.com/#Mass_29>
> ns1:satisfies <ns1://Example#R1> ;
> ns1:run_id ns1:29 .
> ns1:29 a ns1:run ;
> ns1:time "2018-04-12T19:43:14.702"^^xsd:dateTime .
> ns1:799fdfc a ns1:run ;
> ns1:time "2018-04-13T16:55:47-05:00"^^xsd:dateTime .
> {code}
> This query:
> {code:java}
> PREFIX ns1: <http://example.com/ns1#>
> SELECT ?s ?run ?id 
> WHERE {
> ?s a ns1:type_ .
> {
> SELECT ?id
> WHERE {
> values ?id { ns1:799fdfc }
> } LIMIT 1
> }
> OPTIONAL {
> ?s ns1:sb ?run .
> ?run ns1:run_id ?id .
> }
> }
> {code}
> produces 1 result, whereas switching the inner SELECT and OPTIONAL:
> {code:java}
> PREFIX ns1: <http://example.com/ns1#>
> SELECT ?s ?run ?id 
> WHERE {
> ?s a ns1:type_ .
> OPTIONAL { ?s ns1:sb ?run . 
> ?run ns1:run_id ?id . }
> {
> SELECT ?id
> WHERE {
> values ?id { ns1:799fdfc }
> } LIMIT 1
> }
> }{code}
>  
> produces no results.
>  
> The spec specifies "In an optional match, either the optional graph pattern 
> matches a graph, thereby defining and adding bindings to one or more 
> solutions, or it leaves a solution unchanged without adding any additional 
> bindings." and "Due to the bottom-up nature of SPARQL query evaluation, the 
> subqueries are evaluated logically first, and the results are projected up to 
> the outer query.", so I don't see how this is the correct behavior.



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