[GitHub] [arrow-datafusion] alamb commented on issue #1160: Support simplification that requires multiple applications of constant folding / simplification

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alamb commented on issue #1160:
URL: https://github.com/apache/arrow-datafusion/issues/1160#issuecomment-952905624


   @rdettai  I think it is still relevant (though the `now()` example will work after #1175)
   
   One (silly) example
   ```
   (expr != NULL) OR (5 > 10)
   ```
   
   We need to apply at least one pass twice to fully simplify
   
   ```
   (expr != NULL) OR (5 > 10)
   (expr != NULL) OR FALSE # after constant evaluation
   NULL OR FALSE           # after simplify
   NULL                    # after second constant evaluation
   ```
   
   In this this case if we applied simplify first and then constant evaluation the expression would be folded completely
   
   However, for other examples if you apply simplification first that is insufficient
   ```
   expr != (5 > NULL)
   expr != (5 > NULL) # after simplification
   expr != NULL       # after constant evaluation
   ```
   
   (would need a second call to simplify now)
   
   


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