alamb commented on code in PR #10330:
URL: https://github.com/apache/datafusion/pull/10330#discussion_r1587503305


##########
datafusion/core/src/execution/context/mod.rs:
##########
@@ -1947,6 +1982,36 @@ impl SessionState {
             .await
     }
 
+    /// Create a [`PhysicalExpr`] from an [`Expr`] after applying type
+    /// coercion, and function rewrites.
+    ///
+    /// Note: The expression is not [simplified]

Review Comment:
   My rationale was that simplification is substantially more expensive due to 
the rewrites required and is not strictly necessary for evaluation, so I felt 
not simplifying would be less surprising
   
   Also, if we are going to do simplification, it might also be reasonable to 
ask "why not other optimization like [comparison cast 
unwrapping](https://docs.rs/datafusion/latest/datafusion/optimizer/unwrap_cast_in_comparison/index.html)"
 too
   
   I think it is important to apply coercion as is very hard to create the 
right expression to get the type exactly aligned resulting in hard to fix 
errors. Same thing for this function rewriting.
   
   I'll add this context to the comments in this PR



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