cloud-fan commented on a change in pull request #32301:
URL: https://github.com/apache/spark/pull/32301#discussion_r638918033
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
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@@ -17,71 +17,155 @@
package org.apache.spark.sql.catalyst.optimizer
+import scala.collection.mutable
+
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.logical._
import org.apache.spark.sql.internal.SQLConf
import org.apache.spark.sql.types._
/**
- * This aims to handle a nested column aliasing pattern inside the
`ColumnPruning` optimizer rule.
- * If a project or its child references to nested fields, and not all the
fields
- * in a nested attribute are used, we can substitute them by alias attributes;
then a project
- * of the nested fields as aliases on the children of the child will be
created.
+ * This aims to handle a nested column aliasing pattern inside the
[[ColumnPruning]] optimizer rule.
+ * If:
+ * - A [[Project]] or its child references nested fields
+ * - Not all of the fields in a nested attribute are used
+ * Then:
+ * - Substitute the nested field references with alias attributes
+ * - Add grandchild [[Project]]s transforming the nested fields to aliases
Review comment:
not related to this PR: we only add a new Project node as grandchild,
but the scan node may still be at the bottom. Do we expect other rules to push
down the Project through other nodes until it reaches the bottom?
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