[GitHub] spark pull request #17251: [SPARK-19910][SQL] `stack` should not reject NULL...

[viirya <gi...@git.apache.org>]

Github user viirya commented on a diff in the pull request:

    https://github.com/apache/spark/pull/17251#discussion_r116932653
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala ---
    @@ -649,6 +650,21 @@ object TypeCoercion {
       }
     
       /**
    +   * Coerces NullTypes in the Stack expression to the column types of the corresponding positions.
    +   */
    +  object StackCoercion extends Rule[LogicalPlan] {
    +    def apply(plan: LogicalPlan): LogicalPlan = plan resolveExpressions {
    +      case s @ Stack(children) if s.childrenResolved && s.hasFoldableRowNums =>
    +        Stack(children.zipWithIndex.map {
    --- End diff --
    
    `children.tail.zipWithIndex.map { ...}`? So we can strip the first case and we don't need do `index - 1` in next case.



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