[GitHub] [spark] cloud-fan commented on a change in pull request #30134: [SPARK-33225][SQL] Extract AliasHelper trait

[GitBox <gi...@apache.org>]

cloud-fan commented on a change in pull request #30134:
URL: https://github.com/apache/spark/pull/30134#discussion_r511926874



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/AliasHelper.scala
##########
@@ -0,0 +1,100 @@
+/*
+ * 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.expressions
+
+import org.apache.spark.sql.catalyst.analysis.MultiAlias
+import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
+import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Project}
+
+/**
+ * Helper methods for collecting and replacing aliases.
+ */
+trait AliasHelper {
+
+  protected def getAliasMap(plan: Project): AttributeMap[Alias] = {
+    // Create a map of Aliases to their values from the child projection.
+    // e.g., 'SELECT a + b AS c, d ...' produces Map(c -> Alias(a + b, c)).
+    getAliasMap(plan.projectList)
+  }
+
+  protected def getAliasMap(plan: Aggregate): AttributeMap[Alias] = {
+    // Find all the aliased expressions in the aggregate list that don't include any actual
+    // AggregateExpression or PythonUDF, and create a map from the alias to the expression
+    val aliasMap = plan.aggregateExpressions.collect {
+      case a: Alias if a.child.find(e => e.isInstanceOf[AggregateExpression] ||
+        PythonUDF.isGroupedAggPandasUDF(e)).isEmpty =>
+        (a.toAttribute, a)
+    }
+    AttributeMap(aliasMap)
+  }
+
+  protected def getAliasMap(exprs: Seq[NamedExpression]): AttributeMap[Alias] = {
+    // Create a map of Aliases to their values from the child projection.
+    // e.g., 'SELECT a + b AS c, d ...' produces Map(c -> Alias(a + b, c)).
+    AttributeMap(exprs.collect { case a: Alias => (a.toAttribute, a) })
+  }
+
+  /**
+   * Replace all attributes, that reference an alias, with the aliased expression
+   */
+  protected def replaceAlias(
+    expr: Expression,

Review comment:
       nit: 4 space indentation




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