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https://issues.apache.org/jira/browse/JENA-90?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13084081#comment-13084081
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Andreas Schultz commented on JENA-90:
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About not needing a set of already seen bindings: This would only be true if
all variables in the Select clause were also part of the Order By. In general a
set would still be needed. The optimization in the general case would be to
clear this set every time the variable bindings used in the Order By change.
> Use OpReduce instead of OpDistinct for DISTINCT + ORDER BY queries
> ------------------------------------------------------------------
>
> Key: JENA-90
> URL: https://issues.apache.org/jira/browse/JENA-90
> Project: Jena
> Issue Type: Improvement
> Components: ARQ
> Reporter: Paolo Castagna
> Priority: Trivial
> Labels: arq, optimizer, sparql
>
> ARQ's optimizer could use an OpReduce instead of OpDistinct if a query is
> DISTINCT + ORDER BY.
> OpReduce removes adjacent duplicates and it does not require a set of already
> seen bindings as the current OpDistinct implementation does.
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