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

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

alamb commented on code in PR #3721:
URL: https://github.com/apache/arrow-datafusion/pull/3721#discussion_r988372089


##########
datafusion/optimizer/src/type_coercion.rs:
##########
@@ -816,6 +830,55 @@ mod test {
         Ok(())
     }
 
+    #[test]
+    fn concat_for_type_coercion() -> Result<()> {
+        use datafusion_expr::BuiltinScalarFunction::{Concat, ConcatWithSeparator};
+
+        let empty = empty_with_type(DataType::Utf8);
+        let args = vec![col("a"), lit("b"), lit(true), lit(false), lit(13)];
+
+        // concat
+        {
+            let expr = Expr::ScalarFunction {
+                fun: Concat,
+                args: args.clone(),
+            };

Review Comment:
   I think you can use the `concat` builder function here https://docs.rs/datafusion/12.0.0/datafusion/logical_plan/fn.concat.html
   
   ```suggestion
               let expr = concat(args.clone());
   ```
   



##########
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:
   I wonder if we should do something with `LargeUtf8`?
   
   Also, would it make sense to check the types before `clone()`ing them to do a cast that might not be needed?



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