Andy Grove created ARROW-6892:
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             Summary: [Rust] [DataFusion] Implement optimizer rule to remove 
redundant projections
                 Key: ARROW-6892
                 URL: https://issues.apache.org/jira/browse/ARROW-6892
             Project: Apache Arrow
          Issue Type: New Feature
          Components: Rust, Rust - DataFusion
            Reporter: Andy Grove
             Fix For: 1.0.0


Currently we have code in the SQL query planner that wraps aggregate queries in 
a projection (if needed) to preserve the order of the final results. This is 
needed because the aggregate query execution always returns a result with 
grouping expressions first and then aggregate expressions.

It would be better (simpler, more readable code) to always wrap aggregates in 
projections and have an optimizer rule to remove redundant projections. There 
are likely other use cases where redundant projections might exist too.



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