[SPARK-17849] [SQL] Fix NPE problem when using grouping sets

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

@@ -298,10 +298,14 @@ class Analyzer(
           case other => Alias(other, other.toString)()
         }
 
-        val nonNullBitmask = x.bitmasks.reduce(_ & _)
+        // The left most bit in the bitmasks corresponds to the last expression in groupByAliases
+        // with 0 indicating this expression is in the grouping set. The following line of code
+        // calculates the bit mask representing the expressions that exist in all the grouping sets.
+        val nonNullBitmask = ~ x.bitmasks.reduce(_ | _)
 
+        val attrLength = groupByAliases.length
         val expandedAttributes = groupByAliases.zipWithIndex.map { case (a, idx) =>
-          a.toAttribute.withNullability((nonNullBitmask & 1 << idx) == 0)
+          a.toAttribute.withNullability((nonNullBitmask & 1 << (attrLength - idx - 1)) == 0)
         }
 
         val expand = Expand(x.bitmasks, groupByAliases, expandedAttributes, gid, x.child)

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

@@ -0,0 +1,17 @@
+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);
+
+-- SPARK-17849: grouping set throws NPE #1
+SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS (());
+
+-- SPARK-17849: grouping set throws NPE #2
+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));
+
+
+

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

@@ -0,0 +1,42 @@
+-- Automatically generated by SQLQueryTestSuite
+-- Number of queries: 4
+
+
+-- !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)
+-- !query 0 schema
+struct<>
+-- !query 0 output
+
+
+
+-- !query 1
+SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS (())
+-- !query 1 schema
+struct<a:string,b:string,c:string,count(d):bigint>
+-- !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))
+-- !query 2 schema
+struct<a:string,b:string,c:string,count(d):bigint>
+-- !query 2 output
+1	NULL	NULL	1
+4	NULL	NULL	1
+7	NULL	NULL	1
+
+
+-- !query 3
+SELECT a, b, c, count(d) FROM grouping GROUP BY a, b, c GROUPING SETS ((c))
+-- !query 3 schema
+struct<a:string,b:string,c:string,count(d):bigint>
+-- !query 3 output
+NULL	NULL	3	1
+NULL	NULL	6	1
+NULL	NULL	9	1