[GitHub] [arrow-datafusion] alamb commented on issue #2181: [Discuss] Add struct `Query` for datafusion

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alamb commented on issue #2181:
URL: https://github.com/apache/arrow-datafusion/issues/2181#issuecomment-1093135208

   @jackwener  I am not sure about the need for `Query` -- if there is one, perhaps we can combine it with what @andygrove  is working on in https://github.com/apache/arrow-datafusion/pull/2172
   
   I was imagining that a query like this
   
   ```sql
   SELECT f.x, sq.a FROM foo as f JOIN (select a from bar) as sq ON (f.x = sq.a),
   ```
   
   results in a logical plan like this:
   ```
   Projection(f.x, sq.a)
     --> Join(Inner f.x = sq.a)
       --> TableScan(foo)
       --> Projection(a)  <--- Here is where the "subquery"'s LogicalPlan is attached 
         --> TableScan(bar)
   ```
   
   Similarly for
   ```sql
   SELECT f.x  FROM foo as f WHERE f.x IN  (select a from bar) as sq;
   ```
   
   results in a logical plan like this:
   ```
   Projection(f.x, sq.a)
     --> Join(Semi f.x = sq.a)
       --> TableScan(foo)
       --> Projection(a)  <--- Here is where the "subquery"'s LogicalPlan is attached 
         --> TableScan(bar)
   ```


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