[GitHub] [spark] peter-toth commented on a diff in pull request #37525: [SPARK-40086][SQL] Improve AliasAwareOutputPartitioning to take all aliases into account

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

peter-toth commented on code in PR #37525:
URL: https://github.com/apache/spark/pull/37525#discussion_r947860136


##########
sql/core/src/main/scala/org/apache/spark/sql/execution/AliasAwareOutputExpression.scala:
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@@ -16,24 +16,56 @@
  */
 package org.apache.spark.sql.execution
 
-import org.apache.spark.sql.catalyst.expressions.{Alias, Expression, NamedExpression, SortOrder}
-import org.apache.spark.sql.catalyst.plans.physical.{HashPartitioning, Partitioning, PartitioningCollection, UnknownPartitioning}
+import scala.collection.mutable
+
+import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, Expression, NamedExpression, SortOrder}
+import org.apache.spark.sql.catalyst.plans.logical.LeafNode
+import org.apache.spark.sql.catalyst.plans.physical.{Partitioning, PartitioningCollection, UnknownPartitioning}
 
 /**
  * A trait that provides functionality to handle aliases in the `outputExpressions`.
  */
 trait AliasAwareOutputExpression extends UnaryExecNode {
   protected def outputExpressions: Seq[NamedExpression]
 
-  private lazy val aliasMap = outputExpressions.collect {
-    case a @ Alias(child, _) => child.canonicalized -> a.toAttribute
-  }.toMap
+  private lazy val aliasMap = {
+    val aliases = mutable.Map[Expression, mutable.ListBuffer[Attribute]]()
+    // Add aliases to the map. If multiple alias is defined for a source attribute then add all.
+    outputExpressions.foreach {
+      case a @ Alias(child, _) =>
+        // This prepend is needed to make the first element of the `ListBuffer` point to the last
+        // occurrence of an aliased child. This is to keep the previous behavior:
+        // - when we return `Partitioning`s in `outputPartitioning()`, the first should be same as
+        //   it was previously
+        // - when we return a `SortOrder` in `outputOrdering()`, it should be should be same as
+        //   previously
+        a.toAttribute +=: aliases.getOrElseUpdate(child.canonicalized, mutable.ListBuffer.empty)
+      case _ =>
+    }
+    // Append identity mapping of an attribute to the map if both the attribute and its aliased
+    // version can be found in `outputExpressions`.
+    outputExpressions.foreach {
+      case a: Attribute if aliases.contains(a.canonicalized) => aliases(a.canonicalized) += a
+      case _ =>
+    }
+    aliases
+  }
 
   protected def hasAlias: Boolean = aliasMap.nonEmpty
 
-  protected def normalizeExpression(exp: Expression): Expression = {
+  // This function returns a limited number (64) of alternatives to mapped `exp`.

Review Comment:
   sure, done in https://github.com/apache/spark/pull/37525/commits/7266347040cf6af77190c47d91854638aa8a046d, let me know if new conf name doesn't fit



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