[SPARK-19509][SQL] Grouping Sets do not respect nullable grouping columns

## What changes were proposed in this pull request?
The analyzer currently does not check if a column used in grouping sets is actually nullable itself. This can cause the nullability of the column to be incorrect, which can cause null pointer exceptions down the line. This PR fixes that by also consider the nullability of the column.

This is only a problem for Spark 2.1 and below. The latest master uses a different approach.

Closes #16874

## How was this patch tested?
Added a regression test to `SQLQueryTestSuite.grouping_set`.

Author: Herman van Hovell <[email protected]>

Closes #16873 from hvanhovell/SPARK-19509.

(cherry picked from commit a3d5300)
Signed-off-by: Herman van Hovell <[email protected]>

Author: Stan Zhai

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -313,7 +313,8 @@ class Analyzer(
 
         val attrLength = groupByAliases.length
         val expandedAttributes = groupByAliases.zipWithIndex.map { case (a, idx) =>
-          a.toAttribute.withNullability(((nullBitmask >> (attrLength - idx - 1)) & 1) == 1)
+          val canBeNull = ((nullBitmask >> (attrLength - idx - 1)) & 1) == 1
+          a.toAttribute.withNullability(a.nullable || canBeNull)
         }
 
         val expand = Expand(x.bitmasks, groupByAliases, expandedAttributes, gid, x.child)

sql/core/src/test/resources/sql-tests/inputs/grouping_set.sql

@@ -2,7 +2,12 @@ CREATE TEMPORARY VIEW grouping AS SELECT * FROM VALUES
   ("1", "2", "3", 1),
   ("4", "5", "6", 1),
   ("7", "8", "9", 1)
-  as grouping(a, b, c, d);
+  AS grouping(a, b, c, d);
+
+CREATE TEMPORARY VIEW grouping_null AS SELECT * FROM VALUES
+  CAST(NULL AS STRING),
+  CAST(NULL AS STRING)
+  AS T(e);
 
 -- SPARK-17849: grouping set throws NPE #1
 SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS (());
@@ -13,5 +18,8 @@ SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((a));
 -- SPARK-17849: grouping set throws NPE #3
 SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((c));
 
+-- SPARK-19509: grouping set should honor input nullability
+SELECT COUNT(1) FROM grouping_null GROUP BY e GROUPING SETS (e);
 
-
+DROP VIEW IF EXISTS grouping;
+DROP VIEW IF EXISTS grouping_null;

sql/core/src/test/resources/sql-tests/results/grouping_set.sql.out

@@ -1,42 +1,77 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 4
+-- Number of queries: 8
 
 
 -- !query 0
 CREATE TEMPORARY VIEW grouping AS SELECT * FROM VALUES
   ("1", "2", "3", 1),
   ("4", "5", "6", 1),
   ("7", "8", "9", 1)
-  as grouping(a, b, c, d)
+  AS grouping(a, b, c, d)
 -- !query 0 schema
 struct<>
 -- !query 0 output
 
 
 
 -- !query 1
-SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS (())
+CREATE TEMPORARY VIEW grouping_null AS SELECT * FROM VALUES
+  CAST(NULL AS STRING),
+  CAST(NULL AS STRING)
+  AS T(e)
 -- !query 1 schema
-struct<a:string,b:string,c:string,count(d):bigint>
+struct<>
 -- !query 1 output
-NULL	NULL	NULL	3
+
 
 
 -- !query 2
-SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((a))
+SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS (())
 -- !query 2 schema
 struct<a:string,b:string,c:string,count(d):bigint>
 -- !query 2 output
+NULL	NULL	NULL	3
+
+
+-- !query 3
+SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((a))
+-- !query 3 schema
+struct<a:string,b:string,c:string,count(d):bigint>
+-- !query 3 output
 1	NULL	NULL	1
 4	NULL	NULL	1
 7	NULL	NULL	1
 
 
--- !query 3
+-- !query 4
 SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((c))
--- !query 3 schema
+-- !query 4 schema
 struct<a:string,b:string,c:string,count(d):bigint>
--- !query 3 output
+-- !query 4 output
 NULL	NULL	3	1
 NULL	NULL	6	1
 NULL	NULL	9	1
+
+
+-- !query 5
+SELECT COUNT(1) FROM grouping_null GROUP BY e GROUPING SETS (e)
+-- !query 5 schema
+struct<count(1):bigint>
+-- !query 5 output
+2
+
+
+-- !query 6
+DROP VIEW IF EXISTS grouping
+-- !query 6 schema
+struct<>
+-- !query 6 output
+
+
+
+-- !query 7
+DROP VIEW IF EXISTS grouping_null
+-- !query 7 schema
+struct<>
+-- !query 7 output
+