address comments.

Author: gatorsmile

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -320,15 +320,12 @@ object ColumnPruning extends Rule[LogicalPlan] {
       output1.zip(output2).forall(pair => pair._1.semanticEquals(pair._2))
 
   def apply(plan: LogicalPlan): LogicalPlan = plan transform {
-    // Prunes the unused columns from project list of Project/Aggregate/Window/Expand
+    // Prunes the unused columns from project list of Project/Aggregate/Expand
     case p @ Project(_, p2: Project) if (p2.outputSet -- p.references).nonEmpty =>
       p.copy(child = p2.copy(projectList = p2.projectList.filter(p.references.contains)))
     case p @ Project(_, a: Aggregate) if (a.outputSet -- p.references).nonEmpty =>
       p.copy(
         child = a.copy(aggregateExpressions = a.aggregateExpressions.filter(p.references.contains)))
-    case p @ Project(_, w: Window) if (w.windowOutputSet -- p.references).nonEmpty =>
-      p.copy(child = w.copy(
-        windowExpressions = w.windowExpressions.filter(p.references.contains)))
     case a @ Project(_, e @ Expand(_, _, grandChild)) if (e.outputSet -- a.references).nonEmpty =>
       val newOutput = e.output.filter(a.references.contains(_))
       val newProjects = e.projections.map { proj =>
@@ -378,12 +375,17 @@ object ColumnPruning extends Rule[LogicalPlan] {
         p
       }
 
-    // Eliminate no-op Projects
-    case p @ Project(projectList, child) if sameOutput(child.output, p.output) => child
+    // Prune unnecessary window expressions
+    case p @ Project(_, w: Window) if (w.windowOutputSet -- p.references).nonEmpty =>
+      p.copy(child = w.copy(
+        windowExpressions = w.windowExpressions.filter(p.references.contains)))
 
     // Eliminate no-op Window
     case w: Window if w.windowExpressions.isEmpty => w.child
 
+    // Eliminate no-op Projects
+    case p @ Project(projectList, child) if sameOutput(child.output, p.output) => child
+
     // Can't prune the columns on LeafNode
     case p @ Project(_, l: LeafNode) => p