Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/16578#discussion_r148437549
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/JoinFieldExtractionPushdown.scala
---
@@ -0,0 +1,66 @@
+/*
+ * 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 org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet,
NamedExpression}
+import org.apache.spark.sql.catalyst.planning.PhysicalOperation
+import org.apache.spark.sql.catalyst.plans.logical.{Join, LogicalPlan,
Project}
+
+/**
+ * Pushes down aliases to [[expressions.GetStructField]] expressions in a
projection over a join
+ * and its join condition. The original [[expressions.GetStructField]]
expressions are replaced
+ * with references to the pushed down aliases.
+ */
+object JoinFieldExtractionPushdown extends FieldExtractionPushdown {
+ override def apply(plan: LogicalPlan): LogicalPlan =
+ plan transformDown {
+ case op @ PhysicalOperation(projects, Seq(),
+ join @ Join(left, right, joinType, Some(joinCondition))) =>
+ val fieldExtractors = (projects :+
joinCondition).flatMap(getFieldExtractors).distinct
+
+ if (fieldExtractors.nonEmpty) {
+ val (aliases, substituteAttributes) =
constructAliasesAndSubstitutions(fieldExtractors)
--- End diff --
We can return original plan if `aliases` is empty.
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