beliefer commented on code in PR #42223:
URL: https://github.com/apache/spark/pull/42223#discussion_r1284414503


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CombineJoinedAggregates.scala:
##########
@@ -0,0 +1,132 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.optimizer
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.sql.catalyst.expressions.{Alias, And, Attribute, 
AttributeMap, Expression, NamedExpression, Or}
+import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
+import org.apache.spark.sql.catalyst.plans.{Cross, FullOuter, Inner, JoinType, 
LeftOuter, RightOuter}
+import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Filter, Join, 
LeafNode, LogicalPlan, Project, SerializeFromObject}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.catalyst.trees.TreePattern.{AGGREGATE, JOIN}
+
+/**
+ * This rule eliminates the [[Join]] if all the join side are [[Aggregate]]s 
by combine these
+ * [[Aggregate]]s. This rule also support the nested [[Join]], as long as all 
the join sides for
+ * every [[Join]] are [[Aggregate]]s.
+ *
+ * Note: this rule doesn't following cases:
+ * 1. One of the to be merged two [[Aggregate]]s with child [[Filter]] and the 
other one is not.

Review Comment:
   In most cases, the `f(c)` are different. e.g. `f1(c)`, `f2(c)` and so on.



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