[GitHub] [spark] cloud-fan commented on a diff in pull request #42223: [SPARK-44571][SQL] Eliminate the Join by combine multiple Aggregates

["cloud-fan (via GitHub)" <gi...@apache.org>]

cloud-fan commented on code in PR #42223:
URL: https://github.com/apache/spark/pull/42223#discussion_r1280715232


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CombineJoinedAggregates.scala:
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@@ -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.
+ * 2. The upstream node of these [[Aggregate]]s to be merged exists [[Join]].
+ */
+object CombineJoinedAggregates extends Rule[LogicalPlan] with MergeScalarSubqueriesHelper {
+
+  private def isSupportedJoinType(joinType: JoinType): Boolean =
+    Seq(Inner, Cross, LeftOuter, RightOuter, FullOuter).contains(joinType)
+
+  // Merge the multiple Aggregates.
+  private def mergePlan(
+      left: LogicalPlan,
+      right: LogicalPlan): Option[(LogicalPlan, AttributeMap[Attribute], Seq[Expression])] = {
+    (left, right) match {
+      case (la: Aggregate, ra: Aggregate) =>
+        val mergedChildPlan = mergePlan(la.child, ra.child)
+        mergedChildPlan.map { case (newChild, outputMap, filters) =>
+          val rightAggregateExprs = ra.aggregateExpressions.map(mapAttributes(_, outputMap))
+
+          val mergedAggregateExprs = if (filters.length == 2) {
+            Seq(
+              (la.aggregateExpressions, filters.head),
+              (rightAggregateExprs, filters.last)
+            ).flatMap { case (aggregateExpressions, propagatedFilter) =>
+              aggregateExpressions.map { ne =>
+                ne.transform {
+                  case ae @ AggregateExpression(_, _, _, filterOpt, _) =>
+                    val newFilter = filterOpt.map { filter =>
+                      And(filter, propagatedFilter)

Review Comment:
   the old query evaluates `Filter` first, we should keep it and here it should be `And(propagatedFilter, filter)`



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