[GitHub] [arrow-datafusion] jorgecarleitao commented on pull request #2257: Move logical expression type-coercion code from `physical-expr` crate to `expr` crate

[GitBox <gi...@apache.org>]

jorgecarleitao commented on PR #2257:
URL: https://github.com/apache/arrow-datafusion/pull/2257#issuecomment-1101742781

   The background of my thoughts back then was: there are two types of "coercion rules":
   
   * coercion rules that exist as a consequence of the supported ops from the physical engine (e.g. `i32 + i64 -> cast(i32 AS i64) + i64` when the engine does not support `i32 + i64`).
   
   * coercion rules related to the semantic meaning of what the user wants. For example, a user usually wants `sum(Vec<u8>)` to be `u64`, not `u8`, to avoid numeric overflows.
   
   imo the former is part of the step `logical -> physical`, the latter is part of the (run-time) type checking done when performing logical planning for schema resolution (i.e. what schema will the logical plan have)


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