[GitHub] [arrow-datafusion] Dandandan commented on issue #237: Extend & generalize constant folding / evaluation in logical optimizer

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Dandandan commented on issue #237:
URL: https://github.com/apache/arrow-datafusion/issues/237#issuecomment-833824075


   @alamb just picking your brain here - do you think this should be part of the logical optimizations or physical optimizations? 
   I think the suggested route (re-use evaluation code) is only feasible for the physical optimization, not the logical optimization rules.
   
   A way that could work within the current setup for `PhysicalExpr`:
   * Evaluation is implemented for `PhysicalExpr`s not `Exprs`. An empty `RecordBatch` could be used to call into the code and extract the scalar values (if any).
   
   This makes it a bit less useful (still useful nonetheless), as some other optimizations might benefit from constant folding
   
   I am wondering here in general, whether we can/should unify `LogicalPlan`/`PhysicalPlan` `Expr`/`PhysicalExpr` a bit more in order to not have to write two versions of the same thing or being limited in the optimizations / optimization order.


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