[GitHub] [spark] cloud-fan commented on a change in pull request #25239: [SPARK-28495][SQL] AssignableCast: A new type coercion following store assignment rules of ANSI SQL

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cloud-fan commented on a change in pull request #25239: [SPARK-28495][SQL] AssignableCast: A new type coercion following store assignment rules of ANSI SQL
URL: https://github.com/apache/spark/pull/25239#discussion_r306707784
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
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 @@ -1407,3 +1440,12 @@ case class UpCast(child: Expression, dataType: DataType, walkedTypePath: Seq[Str
   extends UnaryExpression with Unevaluable {
   override lazy val resolved = false
 }
+
+/**
+ * Cast the child expression to the target data type, but will throw error if the cast violates
+ * the store assignment rules of ANSI SQL, e.g. string -> int, array -> string.
+ */
+case class AssignableCast(child: Expression, dataType: DataType, walkedTypePath: Seq[String] = Nil)
 
 Review comment:
   can we apply it for the v2 table insertion first? We probably need another PR to apply it for v1 table insertion, as it's a behavior change and needs migration guide.

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