[SPARK-8641][SPARK-12455][SQL] Native Spark Window functions - Follow-up (docs & tests)

This PR is a follow-up for PR https://github.com/apache/spark/pull/9819. It adds documentation for the window functions and a couple of NULL tests.

The documentation was largely based on the documentation in (the source of)  Hive and Presto:
* https://prestodb.io/docs/current/functions/window.html
* https://cwiki.apache.org/confluence/display/Hive/LanguageManual+WindowingAndAnalytics

I am not sure if we need to add the licenses of these two projects to the licenses directory. They are both under the ASL. srowen any thoughts?

cc yhuai

Author: Herman van Hovell <hvanhovell@questtec.nl>

Closes #10402 from hvanhovell/SPARK-8641-docs.

1 files changed, 15 insertions, 0 deletions

diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/WindowQuerySuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/WindowQuerySuite.scala
index c05dbfd760..ea82b8c459 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/WindowQuerySuite.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/WindowQuerySuite.scala
@@ -227,4 +227,19 @@ class WindowQuerySuite extends QueryTest with SQLTestUtils with TestHiveSingleto
         Row("Manufacturer#5", "almond azure blanched chiffon midnight", 23, 315.9225931564038, 315.9225931564038, 46, 99807.08486666666, -0.9978877469246935, -5664.856666666666)))
       // scalastyle:on
   }
+
+  test("null arguments") {
+    checkAnswer(sql("""
+        |select  p_mfgr, p_name, p_size,
+        |sum(null) over(distribute by p_mfgr sort by p_name) as sum,
+        |avg(null) over(distribute by p_mfgr sort by p_name) as avg
+        |from part
+      """.stripMargin),
+      sql("""
+        |select  p_mfgr, p_name, p_size,
+        |null as sum,
+        |null as avg
+        |from part
+        """.stripMargin))
+  }
 }