Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/10577#discussion_r49631075
--- 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 --
I think we should ensure `children.length > 1`, it doesn't make sense to
have a one-child `Union`, we should remove the wrapping union at analysis phase.
cc @marmbrus @rxin
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