Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/4826#discussion_r25639644
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/types/dataTypes.scala ---
@@ -198,6 +198,43 @@ object DataType {
case (left, right) => left == right
}
}
+
+ /**
+ * Compares two types, ignoring compatible nullability of ArrayType,
MapType, StructType.
+ *
+ * Compatible nullability is defined as follows:
+ * - If `from` and `to` are ArrayTypes, `from` has a compatible
nullability with `to`
+ * if and only if `to.containsNull` is true, or both of
`from.containsNull` and
+ * `to.containsNull` are false.
+ * - If `from` and `to` are MapTypes, `from` has a compatible
nullability with `to`
+ * if and only if `to.valueContainsNull` is true, or both of
`from.valueContainsNull` and
+ * `to.valueContainsNull` are false.
+ * - If `from` and `to` are StructTypes, `from` has a compatible
nullability with `to`
+ * if and only if for all every pair of fields, `to.nullable` is true,
or both
+ * of `fromField.nullable` and `toField.nullable` are false.
+ */
+ private[sql] def equalsIgnoreCompatibleNullability(from: DataType, to:
DataType): Boolean = {
--- End diff --
We can introduce a method to the class of `DataType` based on this one
later (I am not sure what will be a good name. I thought about
`compatibleWith`, but I feel it is not very accurate).
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