mgaido91 commented on a change in pull request #23726: [SPARK-26812][SQL]
Report correct nullability for complex datatypes in Union
URL: https://github.com/apache/spark/pull/23726#discussion_r255332358
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
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@@ -230,9 +231,19 @@ case class Union(children: Seq[LogicalPlan]) extends
LogicalPlan {
}
// updating nullability to make all the children consistent
- override def output: Seq[Attribute] =
- children.map(_.output).transpose.map(attrs =>
- attrs.head.withNullability(attrs.exists(_.nullable)))
+ override def output: Seq[Attribute] = {
+ children.map(_.output).transpose.map { attrs =>
+ val firstAttr = attrs.head
+ val outAttr = try {
+ firstAttr.withDataType(attrs.map(_.dataType).reduce(StructType.merge))
+ } catch {
+ // This should never happen, since `output` is called only when the
plan is `resolved`, so
Review comment:
thanks for the comment @dongjoon-hyun. I propose to add a `logError` in
order to ask users to report this error condition and go on with this fallback
logic, in order to ensure that the behavior is the same as before this patch in
unexpected conditions (so no behavior change) but at the same time we can
detect this problem. Do you agree?
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