alamb opened a new pull request, #8766:
URL: https://github.com/apache/arrow-datafusion/pull/8766

   Draft
   
   ## Which issue does this PR close?
   
   Closes https://github.com/apache/arrow-datafusion/issues/8738
   
   ## Rationale for this change
   This is a second sketch of how to close 
https://github.com/apache/arrow-datafusion/issues/8738
   
   https://github.com/apache/arrow-datafusion/pull/8291 / 
https://github.com/apache/arrow-datafusion/issues/7647 changed DataFusion's 
Grouping operator so that it never dictionary encoded the output grouping 
columns. 
   
   Previously, the types of the input grouping expressions were the same as the 
types of the output group by
   
   The idea I think is that since the values in the group columns are unique, 
there is no reason to dictionary encode them (as each dictionary entry would 
have a single value). I actually am not sure about this for reasons I will 
explain shortly. 
   
   ## What changes are included in this PR?
   
   This PR changes `LogicalPlan::Aggregate` and `LogicalPlan::Distinct` (which 
both use the HashAggregate `ExecutionPlan`) to report a schema that is 
dictionary unencoded. 
   
   ## Are these changes tested?
   Yes, there is a regression test. 
   
   ## Are there any user-facing changes?
   
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