[GitHub] [arrow-datafusion] HaoYang670 commented on a diff in pull request #3721: Add type coercion rule for `concat` and `concat_ws`

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

HaoYang670 commented on code in PR #3721:
URL: https://github.com/apache/arrow-datafusion/pull/3721#discussion_r988486604


##########
datafusion/optimizer/src/type_coercion.rs:
##########
@@ -398,6 +398,20 @@ impl ExprRewriter for TypeCoercionRewriter {
                     }
                 }
             }
+            Expr::ScalarFunction { fun, args } => match fun {
+                BuiltinScalarFunction::Concat
+                | BuiltinScalarFunction::ConcatWithSeparator => {
+                    let new_args = args

Review Comment:
   > would it make sense to check the types before clone()ing them to do a cast that might not be needed?
   
   I think this has been done in the `cast_to` function:
   ```rust
   fn cast_to<S: ExprSchema>(self, cast_to_type: &DataType, schema: &S) -> Result<Expr> {
       // TODO(kszucs): most of the operations do not validate the type correctness
       // like all of the binary expressions below. Perhaps Expr should track the
       // type of the expression?
       let this_type = self.get_type(schema)?;
       if this_type == *cast_to_type {
           Ok(self)
   ...
   }
   ```



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