Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/10577#discussion_r49629259 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicOperators.scala --- @@ -123,6 +115,39 @@ case class Except(left: LogicalPlan, right: LogicalPlan) extends SetOperation(le override def output: Seq[Attribute] = left.output } +/** Factory for constructing new `Union` nodes. */ +object Union { + def apply(left: LogicalPlan, right: LogicalPlan): Union = { + Union (left :: right :: Nil) + } +} + +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 lazy val resolved: Boolean = { + lazy val allChildrenCompatible: Boolean = + children.tail.forall( child => + // compare the attribute number with the first child + child.output.length == children.head.output.length && + // compare the data types with the first child + child.output.zip(children.head.output).forall { + case (l, r) => l.dataType == r.dataType } + ) + + childrenResolved && allChildrenCompatible --- End diff -- how about also make sure `children.nonEmpty`?
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