[I] Support nested recursive CTEs [datafusion]

["Tpt (via GitHub)" <gi...@apache.org>]

Tpt opened a new issue, #18955:
URL: https://github.com/apache/datafusion/issues/18955

   ### Is your feature request related to a problem or challenge?
   
   SPARQL support nested property paths (i.e. regular expressions in the graph). For example `(p1 / p2+)+` to state "follow and edge labeled p1 then any number of edges labeled p2, all of this any number of times".
   
   This can be implemented in DataFusion using nested recursive CTEs like
   ```sql
   WITH RECURSIVE outer_cte AS (
       SELECT start, end FROM graph WHERE label = 'p1' 
       UNION (
           WITH  RECURSIVE nested_cte AS (
              SELECT start, end FROM graph WHERE label = 'p2' 
              UNION
              SELECT nested_cte.start AS start, graph.end AS end FROM nested_cte, graph WHERE nested_cte.end = graph.start AND graph.label = 'p2'
            )
       SELECT outer_cte.start AS start, nested_cte.end AS end FROM outer_cte, nested_cte WHERE outer_cte.end = nested_cte.start
      )
   ) SELECT * FROM outer_cte;
   ```
   where `graph(start, label, end)` is the edge table
   
   Sadly, nested CTEs are not supported in DataFusion yet
   
   ### Describe the solution you'd like
   
   Enable nested recursive CTEs. A quick implementation might be to give each `WorkSet` plan node a name and use this name to allow the `RecursiveQueryExec` node to pick the correct `WorkSetExec` node to set 
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   _No response_


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Re: [I] Support nested recursive CTEs [datafusion]

["Jefffrey (via GitHub)" <gi...@apache.org>]

Jefffrey closed issue #18955: Support nested recursive CTEs
URL: https://github.com/apache/datafusion/issues/18955


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