cloud-fan commented on a change in pull request #34025:
URL: https://github.com/apache/spark/pull/34025#discussion_r710838554
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/types/StructType.scala
##########
@@ -559,52 +559,82 @@ object StructType extends AbstractDataType {
case _ => dt
}
+ /**
+ * This leverages `merge` to merge data types for UNION operator by
specializing
+ * the handling of struct types to follow UNION semantics.
+ */
+ private[sql] def unionLikeMerge(left: DataType, right: DataType): DataType =
+ mergeInternal(left, right, (s1: StructType, s2: StructType) => {
+ val leftFields = s1.fields
+ val rightFields = s2.fields
+ require(leftFields.size == rightFields.size, "To merge nullability, " +
+ "two structs must have same number of fields.")
+
+ val newFields = leftFields.zip(rightFields).map {
+ case (leftField@StructField(_, leftType, leftNullable, _),
+ _@StructField(_, rightType, rightNullable, _)) =>
Review comment:
nit:
```
case (leftField, rightField) =>
leftField.copy(
dataType = unionLikeMerge(leftField.dataType, rightField.dataType),
nullable = ...
```
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