maropu commented on a change in pull request #30018:
URL: https://github.com/apache/spark/pull/30018#discussion_r508993694
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -477,6 +478,25 @@ object RemoveRedundantAliases extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = removeRedundantAliases(plan,
AttributeSet.empty)
}
+/**
+ * Remove redundant aggregates from a query plan. A redundant aggregate is an
aggregate whose
+ * only goal is to keep distinct values, while its parent aggregate would
ignore duplicate values.
+ */
+object RemoveRedundantAggregates extends Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
Review comment:
> transformUp can handle more than two consecutive aggregates in a
single iteration.
You meant that `transformUp` can transform `A1(A2(A3(...))) => A1()` in a
single iteration? Probably, I miss some conditions for the case you described
above, so could you give me a concrete query example for it?
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