[SPARK-16195][SQL] Allow users to specify empty over clause in window expressions through dataset API

## What changes were proposed in this pull request?
Allow to specify empty over clause in window expressions through dataset API

In SQL, its allowed to specify an empty OVER clause in the window expression.

```SQL
select area, sum(product) over () as c from windowData
where product > 3 group by area, product
having avg(month) > 0 order by avg(month), product
```
In this case the analytic function sum is presented based on all the rows of the result set

Currently its not allowed through dataset API and is handled in this PR.

## How was this patch tested?

Added a new test in DataframeWindowSuite

Author: Dilip Biswal <dbiswal@us.ibm.com>

Closes #13897 from dilipbiswal/spark-empty-over.

1 files changed, 12 insertions, 0 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameWindowSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameWindowSuite.scala
index 9a1aa46947..c6f8c3ad3f 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameWindowSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameWindowSuite.scala
@@ -245,6 +245,18 @@ class DataFrameWindowSuite extends QueryTest with SharedSQLContext {
       Seq(Row("a", 6, 9), Row("b", 9, 6)))
   }
 
+  test("SPARK-16195 empty over spec") {
+    val df = Seq(("a", 1), ("a", 1), ("a", 2), ("b", 2)).
+      toDF("key", "value")
+    df.createOrReplaceTempView("window_table")
+    checkAnswer(
+      df.select($"key", $"value", sum($"value").over(), avg($"value").over()),
+      Seq(Row("a", 1, 6, 1.5), Row("a", 1, 6, 1.5), Row("a", 2, 6, 1.5), Row("b", 2, 6, 1.5)))
+    checkAnswer(
+      sql("select key, value, sum(value) over(), avg(value) over() from window_table"),
+      Seq(Row("a", 1, 6, 1.5), Row("a", 1, 6, 1.5), Row("a", 2, 6, 1.5), Row("b", 2, 6, 1.5)))
+  }
+
   test("window function with udaf") {
     val udaf = new UserDefinedAggregateFunction {
       def inputSchema: StructType = new StructType()