mihailom-db commented on code in PR #45383:
URL: https://github.com/apache/spark/pull/45383#discussion_r1546413940

@@ -0,0 +1,135 @@
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.spark.sql.catalyst.analysis
+import javax.annotation.Nullable
+import scala.annotation.tailrec
+import org.apache.spark.sql.catalyst.analysis.TypeCoercion.hasStringType
+import org.apache.spark.sql.catalyst.expressions.{BinaryExpression, Cast, 
ComplexTypeMergingExpression, CreateArray, ExpectsInputTypes, Expression, 
Predicate, SortOrder}
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{AbstractDataType, ArrayType, DataType, 
+object CollationTypeCasts extends TypeCoercionRule {
+  override val transform: PartialFunction[Expression, Expression] = {
+    case e if !e.childrenResolved => e
+    case sc @ (_: BinaryExpression
+              | _: Predicate
+              | _: SortOrder
+              | _: ExpectsInputTypes
+              | _: ComplexTypeMergingExpression) =>
+      val newChildren = collateToSingleType(sc.children)
+      sc.withNewChildren(newChildren)
+    case pesc @ (_: CreateArray) =>

Review Comment:
   How I understood it, arrays are bulding blocks for types as well. The 
difference is that arrays have to be built from some different types which 
makes them complex. But `substring`, `concat`, etc. are functions that return 
something based on a transformation behaviour. In other words, CreateArray is 
not even considering the the values, it only builds a new 'basic' block. That 
is why I am also concerned with what we want to do with Elt, do we want to do 
casting or just propagation of inputs, as it does not change any string, but 
only takes a specific value from the given index. But again, this differs from 
array access, as arrays need to have a single type for all input expressions.

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