[jira] [Commented] (JENA-111) Improving TopN optimization in case of an intermediate OpModifier

["Andy Seaborne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-111?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13098278#comment-13098278 ] 

Andy Seaborne commented on JENA-111:
------------------------------------

For reference,  the full possible stack of modifiers possible in a single level of SPARQL query is:

  Limit/Offset
     Distinct/reduce
       project
         OrderBy
            Bindings
                having
                   select expressions
                         group

but, by using subSELECTs, you can write any sequence you want.

SELECT DISTINCT ?x 
{
   ?x :p 123 .
} ORDER BY ?x LIMIT 2

  (slice _ 2
    (distinct
      (project (?x)
        (order (?x)
          (bgp (triple ?x :p 123))))))


> Improving TopN optimization in case of an intermediate OpModifier
> -----------------------------------------------------------------
>
>                 Key: JENA-111
>                 URL: https://issues.apache.org/jira/browse/JENA-111
>             Project: Jena
>          Issue Type: Improvement
>          Components: ARQ
>            Reporter: Sara Magliacane
>            Assignee: Paolo Castagna
>            Priority: Minor
>              Labels: arq, optimization
>         Attachments: topk_project.patch
>
>
> In the TopN optimization (Jena-89)  it would be useful to handle also the case in which there are some other OpModifiers (I think they are the only category of Ops that can be in that position in the tree) between Slice and Order By, for example OpProject:
> (slice _1
>   (project ?s ...
>     (order by <condition>
> -> 
> (project ?s ...
>   (top 1 <condition>

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