Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/16757#discussion_r99357536
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -154,56 +155,108 @@ class SimpleTestOptimizer extends Optimizer(
new SimpleCatalystConf(caseSensitiveAnalysis = true))
/**
- * Removes the Project only conducting Alias of its child node.
- * It is created mainly for removing extra Project added in
EliminateSerialization rule,
- * but can also benefit other operators.
+ * Remove redundant aliases from a query plan. A redundant alias is an
alias that does not change
+ * the name or metadata of a column, and does not deduplicate it.
*/
-object RemoveAliasOnlyProject extends Rule[LogicalPlan] {
+object RemoveRedundantAliases extends Rule[LogicalPlan] {
+
/**
- * Returns true if the project list is semantically same as child
output, after strip alias on
- * attribute.
+ * Replace the attributes in an expression using the given mapping.
*/
- private def isAliasOnly(
- projectList: Seq[NamedExpression],
- childOutput: Seq[Attribute]): Boolean = {
- if (projectList.length != childOutput.length) {
- false
- } else {
- stripAliasOnAttribute(projectList).zip(childOutput).forall {
- case (a: Attribute, o) if a semanticEquals o => true
- case _ => false
- }
+ private def createAttributeMapping(current: LogicalPlan, next:
LogicalPlan)
--- End diff --
can you explain what `current` and `next` means here?
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