cloud-fan commented on a change in pull request #33284:
URL: https://github.com/apache/spark/pull/33284#discussion_r669608171
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/subquery.scala
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@@ -701,3 +702,43 @@ object RewriteLateralSubquery extends Rule[LogicalPlan] {
Join(left, newRight, joinType, newCond, JoinHint.NONE)
}
}
+
+/**
+ * This rule optimizes subqueries with OneRowRelation as leaf nodes.
+ */
+object OptimizeOneRowRelationSubquery extends Rule[LogicalPlan] {
+
+ object OneRowSubquery {
+ def unapply(plan: LogicalPlan): Option[Seq[NamedExpression]] = {
+ CollapseProject(EliminateSubqueryAliases(plan)) match {
+ case Project(projectList, _: OneRowRelation) =>
Some(stripOuterReferences(projectList))
+ case _ => None
+ }
+ }
+ }
+
+ /**
+ * Rewrite a subquery expression into one or more expressions. The rewrite
can only be done
+ * if there is no nested subqueries in the subquery plan.
+ */
+ private def rewrite(plan: LogicalPlan): LogicalPlan =
plan.transformUpWithSubqueries {
Review comment:
do we need to handle nested subqueries here? I think the rule
`OptimizeSubqueries` will run this rule again to optimize nested subqueries.
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