mihailom-db commented on code in PR #45383:
URL: https://github.com/apache/spark/pull/45383#discussion_r1530301512


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala:
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@@ -764,6 +773,184 @@ abstract class TypeCoercionBase {
     }
   }
 
+  object CollationTypeCasts extends TypeCoercionRule {
+    override val transform: PartialFunction[Expression, Expression] = {
+      case e if !e.childrenResolved => e
+
+      case checkCastWithIndeterminate: Concat
+        if shouldCast(checkCastWithIndeterminate.children) =>
+        val newChildren =
+          collateToSingleType(checkCastWithIndeterminate.children, 
failOnIndeterminate = false)
+        checkCastWithIndeterminate.withNewChildren(newChildren)
+
+      case checkCastWithoutIndeterminate@(_: BinaryExpression | _: In | _: 
SortOrder)
+        if shouldCast(checkCastWithoutIndeterminate.children) =>
+        val newChildren = 
collateToSingleType(checkCastWithoutIndeterminate.children)
+        checkCastWithoutIndeterminate.withNewChildren(newChildren)
+
+      case checkIndeterminate@(_: BinaryExpression | _: In | _: SortOrder)
+        if hasIndeterminate(checkIndeterminate.children
+          .filter(e => hasStringType(e.dataType))
+          .map(e => extractStringType(e.dataType))) =>
+        throw QueryCompilationErrors.indeterminateCollationError()
+
+      case checkImplicitCastInputTypes: ImplicitCastInputTypes
+        if checkImplicitCastInputTypes.children.exists(e => 
hasStringType(e.dataType))
+          && checkImplicitCastInputTypes.inputTypes.nonEmpty =>
+        val collationId: Int =
+          getOutputCollation(checkImplicitCastInputTypes
+            .children.filter { e => hasStringType(e.dataType) })
+        val children: Seq[Expression] = checkImplicitCastInputTypes
+          .children.zip(checkImplicitCastInputTypes.inputTypes).map {
+            case (e, st) if hasStringType(st) =>
+              castStringType(e, collationId, Some(st)).getOrElse(e)
+            case (e, TypeCollection(types)) if types.exists(hasStringType) =>
+              types.flatMap{ dt =>
+                if (hasStringType(dt)) {
+                  castStringType(e, collationId, Some(dt))
+                } else {
+                  implicitCast(e, dt)
+                }
+              }.headOption.getOrElse(e)
+            case (in, expected) => implicitCast(in, expected).getOrElse(in)
+          }
+        checkImplicitCastInputTypes.withNewChildren(children)
+
+      case checkExpectsInputType: ExpectsInputTypes

Review Comment:
   I agree and could move implicitCasting from here to `ImpicitTypeCast`. Only 
problem is that we then have to change multiple checks to run 
`getOutputCollation` (e.g. `ConcatCoercion`) as they might cast to 
StringType(0) even though we want collated cast. I was thinking about 
performance issues if this is ok to run check for collationId multiple times in 
different checks? Do you have some idea on how heavy this operation would be to 
the whole casting process, as I am not still quite sure?



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