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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