[GitHub] [arrow] jorgecarleitao commented on pull request #8024: ARROW-9809: [Rust][DataFusion] Fixed type coercion, supertypes and type checking.

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jorgecarleitao commented on pull request #8024:
URL: https://github.com/apache/arrow/pull/8024#issuecomment-678770336


   @alamb , thanks a lot for that insight.
   
   I may have been using the wrong notation here.
   
   I think that we have each columns' type during logical planning: the `LogicalPlanBuilder` always starts with a scan with a well defined (or infered via scan) schema. When a projection is constructed, which requires us to derive a `schema`, we build that schema by deriving the column types from its expressions, via `exprlist_to_fields` (that uses `Expr::to_field` that uses `Expr::get_type(input_schema)`).
   
   As I see it, the type coercer optimizer is casting types being passed to binary operators for the sole purpose of matching numerical types to perform computations, as we do not have kernels for different numerical types (e.g. u16 + u32).


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