1 files changed, 9 insertions, 19 deletions
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
index 5210f42c55..cc62d5e7c8 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
@@ -1663,27 +1663,17 @@ class Analyzer(
         }
       }.toSeq
 
-      // Third, for every Window Spec, we add a Window operator and set currentChild as the
-      // child of it.
-      var currentChild = child
-      var i = 0
-      while (i < groupedWindowExpressions.size) {
-        val ((partitionSpec, orderSpec), windowExpressions) = groupedWindowExpressions(i)
-        // Set currentChild to the newly created Window operator.
-        currentChild =
-          Window(
-            windowExpressions,
-            partitionSpec,
-            orderSpec,
-            currentChild)
-
-        // Move to next Window Spec.
-        i += 1
-      }
+      // Third, we aggregate them by adding each Window operator for each Window Spec and then
+      // setting this to the child of the next Window operator.
+      val windowOps =
+        groupedWindowExpressions.foldLeft(child) {
+          case (last, ((partitionSpec, orderSpec), windowExpressions)) =>
+            Window(windowExpressions, partitionSpec, orderSpec, last)
+        }
 
-      // Finally, we create a Project to output currentChild's output
+      // Finally, we create a Project to output windowOps's output
       // newExpressionsWithWindowFunctions.
-      Project(currentChild.output ++ newExpressionsWithWindowFunctions, currentChild)
+      Project(windowOps.output ++ newExpressionsWithWindowFunctions, windowOps)
     } // end of addWindow
 
     // We have to use transformDown at here to make sure the rule of