Github user JDrit commented on a diff in the pull request:
https://github.com/apache/spark/pull/7478#discussion_r35057227
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/expressions/ResolveVirtualColumn.scala
---
@@ -0,0 +1,37 @@
+/*
+ * 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.expressions
+
+import org.apache.spark.sql.catalyst.analysis._
+import org.apache.spark.sql.catalyst.expressions.{Alias, VirtualColumn}
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.execution.expressions.SparkPartitionID
+
+/**
+ * Used to resolve virtual column attributes and insert the expression for
them. Add case
+ * statements to this for each additional virtual column
+ */
+private[sql] class ResolveVirtualColumn(resolver: Resolver) extends
Rule[LogicalPlan] {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case lPlan: LogicalPlan => lPlan transformExpressionsUp {
+ case u @ UnresolvedAttribute(nameParts) if nameParts.length == 1 &&
+ resolver(nameParts.head, VirtualColumn.sparkPartitionId) =>
SparkPartitionID
--- End diff --
So the query you gave will resolve the outer `spark__partition__id` as a
virtual column, ignoring the alias.
Some other data points:
`select spark__partition__id from table` (where `spark__partition__id` is a
column) will resolve to the column and not the virtual column.
`SELECT a as spark__partition__id from test_table` will resolve the column
`a`
The order of precedence goes, column, virtual_column, alias.
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