Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/17251#discussion_r105514460
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/generators.scala
---
@@ -156,9 +157,21 @@ case class Stack(children: Seq[Expression]) extends
Generator {
}
}
+ private def findDataType(column: Integer): DataType = {
+ // Find the first data type except NullType
+ for (i <- (column + 1) until children.length by numFields) {
+ if (children(i).dataType != NullType) {
+ return children(i).dataType
+ }
+ }
+ // If all values of the column are NullType, use it.
+ children(column + 1).dataType
+ }
+
override def elementSchema: StructType =
StructType(children.tail.take(numFields).zipWithIndex.map {
- case (e, index) => StructField(s"col$index", e.dataType)
+ case (e, index) if e.dataType != NullType =>
StructField(s"col$index", e.dataType)
+ case (_, index) => StructField(s"col$index", findDataType(index))
--- End diff --
`findDataType` is only used when a value of the first row is `NULL`.
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