Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/13906#discussion_r68701768
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -1053,6 +1055,41 @@ object PruneFilters extends Rule[LogicalPlan] with
PredicateHelper {
}
/**
+ * Collapse plans consisting all empty local relations generated by
[[PruneFilters]].
+ * Note that the ObjectProducer/Consumer and direct aggregations are the
exceptions.
+ * {{{
+ * SELECT a, b FROM t WHERE 1=0 GROUP BY a, b ORDER BY a, b ==> empty
result
+ * SELECT SUM(a) FROM t WHERE 1=0 GROUP BY a HAVING COUNT(*)>1 ORDER BY
a (Not optimized)
+ * }}}
+ */
+object CollapseEmptyPlan extends Rule[LogicalPlan] with PredicateHelper {
+ private def isEmptyLocalRelation(plan: LogicalPlan): Boolean =
+ plan.isInstanceOf[LocalRelation] &&
plan.asInstanceOf[LocalRelation].data.isEmpty
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
+ case x if x.isInstanceOf[ObjectProducer] ||
x.isInstanceOf[ObjectConsumer] => x
+
+ // Case 1: If groupingExpressions contains all aggregation
expressions, the result is empty.
+ case a @ Aggregate(ge, ae, child) if isEmptyLocalRelation(child) &&
ae.forall(ge.contains(_)) =>
+ LocalRelation(a.output, data = Seq.empty)
+
+ // Case 2: General aggregations can generate non-empty results.
+ case a: Aggregate => a
+
+ // Case 3: The following non-leaf plans having only empty relations
return empty results.
+ case p: LogicalPlan if p.children.nonEmpty &&
p.children.forall(isEmptyLocalRelation) =>
+ p match {
+ case _: Project | _: Generate | _: Filter | _: Sample | _: Join |
--- End diff --
actually for intersect you only need one child to be empty
for join if it is inner join you just need one child to be empty too
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