Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/17251#discussion_r106329490
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
---
@@ -590,6 +591,23 @@ object TypeCoercion {
}
/**
+ * Coerces NullTypes of a Stack function to the corresponding column
types.
+ */
+ object StackCoercion extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan resolveExpressions {
+ case s @ Stack(children) if s.childrenResolved &&
s.children.head.dataType == IntegerType &&
+ s.children.head.foldable =>
+ val schema = s.elementSchema
+ Stack(children.zipWithIndex.map {
+ case (e, 0) => e
+ case (Literal(null, NullType), index: Int) =>
+ Literal.create(null, schema.fields((index - 1) %
schema.length).dataType)
--- End diff --
we can call `findDataType((index - 1) % s.numFields)` here
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