Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/7957#discussion_r37118409
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -968,3 +961,61 @@ object EliminateSubQueries extends Rule[LogicalPlan] {
case Subquery(_, child) => child
}
}
+
+/**
+ * Cleans up unnecessary Aliases inside the plan. Basically we only need
Alias as a top level
+ * expression in Project(project list) or Aggregate(aggregate expressions)
or
+ * Window(window expressions).
+ */
+object CleanupAliases extends Rule[LogicalPlan] {
+ private def trimAliases(e: Expression): Expression = {
+ var stop = false
+ e.transformDown {
+ // CreateStruct is a special case, we need to retain its top level
Aliases as they decide the
+ // name of StructField. We also need to stop transform down this
expression, or the Aliases
+ // under CreateStruct will be mistakenly trimmed.
+ case c: CreateStruct if !stop =>
+ stop = true
+ c.copy(children = c.children.map(trimNonTopLevelAliases))
+ case c: CreateStructUnsafe if !stop =>
+ stop = true
+ c.copy(children = c.children.map(trimNonTopLevelAliases))
+ case Alias(child, _) if !stop => child
+ }
+ }
+
+ def trimNonTopLevelAliases(e: Expression): Expression = e match {
+ case a: Alias =>
+ Alias(trimAliases(a.child), a.name)(a.exprId, a.qualifiers,
a.explicitMetadata)
+ case other => trimAliases(other)
+ }
+
+ override def apply(plan: LogicalPlan): LogicalPlan = plan
resolveOperators {
+ case Project(projectList, child) =>
+ val cleanedProjectList =
+
projectList.map(trimNonTopLevelAliases(_).asInstanceOf[NamedExpression])
+ Project(cleanedProjectList, child)
+
+ case Aggregate(grouping, aggs, child) =>
+ val cleanedAggs =
aggs.map(trimNonTopLevelAliases(_).asInstanceOf[NamedExpression])
+ Aggregate(grouping.map(trimAliases), cleanedAggs, child)
+
+ case w @ Window(projectList, windowExprs, partitionSpec, orderSpec,
child) =>
+ val cleanedWindowExprs =
+ windowExprs.map(e =>
trimNonTopLevelAliases(e).asInstanceOf[NamedExpression])
+ Window(projectList, cleanedWindowExprs,
partitionSpec.map(trimAliases),
+ orderSpec.map(trimAliases(_).asInstanceOf[SortOrder]), child)
+
+ case other =>
+ var stop = false
--- End diff --
Not for this release, but this makes me think that we are abusing aliases.
I would rather that resolved expressions past the analyzer move the names out
of the subexpressions and into the `CreateStruct` expression itself.
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