Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21687#discussion_r201261400
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -172,6 +172,18 @@ object TypeCoercion {
case _ => None
}
+ /**
+ * The method finds a common type for data types that differ only in
nullable, containsNull
+ * and valueContainsNull flags. If the input types are too different,
None is returned.
+ */
+ def findCommonTypeDifferentOnlyInNullFlags(t1: DataType, t2: DataType):
Option[DataType] = {
--- End diff --
why define the method here as it's only used in
`ComplexTypeMergingExpression`?
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