with GpBy query outer query results need to be further merged

processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java

@@ -199,35 +199,42 @@ public class GroupByQueryQueryToolChest extends QueryToolChest<Row, GroupByQuery
       final GroupByQuery outerQuery = new GroupByQuery.Builder(query)
           .setLimitSpec(query.getLimitSpec().merge(subquery.getLimitSpec()))
           .build();
-      final IncrementalIndex index = makeIncrementalIndex(innerQuery, subqueryResult);
+
+      final IncrementalIndex innerQueryResultIndex = makeIncrementalIndex(innerQuery, subqueryResult);
 
       //Outer query might have multiple intervals, but they are expected to be non-overlapping and sorted which
       //is ensured by QuerySegmentSpec.
       //GroupByQueryEngine can only process one interval at a time, so we need to call it once per interval
       //and concatenate the results.
-      return new ResourceClosingSequence<>(
-          outerQuery.applyLimit(
-              Sequences.concat(
-                  Sequences.map(
-                      Sequences.simple(outerQuery.getIntervals()),
-                      new Function<Interval, Sequence<Row>>()
-                      {
-                        @Override
-                        public Sequence<Row> apply(Interval interval)
-                        {
-                          return engine.process(
-                              outerQuery.withQuerySegmentSpec(
-                                  new MultipleIntervalSegmentSpec(ImmutableList.of(interval))
-                              ),
-                              new IncrementalIndexStorageAdapter(index)
-                          );
-                        }
-                      }
-                  )
+      final IncrementalIndex outerQueryResultIndex = makeIncrementalIndex(
+          outerQuery,
+          Sequences.concat(
+              Sequences.map(
+                  Sequences.simple(outerQuery.getIntervals()),
+                  new Function<Interval, Sequence<Row>>()
+                  {
+                    @Override
+                    public Sequence<Row> apply(Interval interval)
+                    {
+                      return engine.process(
+                          outerQuery.withQuerySegmentSpec(
+                              new MultipleIntervalSegmentSpec(ImmutableList.of(interval))
+                          ),
+                          new IncrementalIndexStorageAdapter(innerQueryResultIndex)
+                      );
+                    }
+                  }
               )
-          ),
-          index
+          )
       );
+
+      innerQueryResultIndex.close();
+
+      return new ResourceClosingSequence<>(
+          outerQuery.applyLimit(postAggregate(query, outerQueryResultIndex)),
+          outerQueryResultIndex
+      );
+
     } else {
       final IncrementalIndex index = makeIncrementalIndex(
           query, runner.run(

processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java

@@ -2809,6 +2809,63 @@ public class GroupByQueryRunnerTest
     TestHelper.assertExpectedObjects(expectedResults, results, "");
   }
 
+  @Test
+  public void testSubqueryWithExtractionFnInOuterQuery()
+  {
+    //https://github.com/druid-io/druid/issues/2556
+    
+    GroupByQuery subquery = GroupByQuery
+        .builder()
+        .setDataSource(QueryRunnerTestHelper.dataSource)
+        .setQuerySegmentSpec(QueryRunnerTestHelper.firstToThird)
+        .setDimensions(Lists.<DimensionSpec>newArrayList(new DefaultDimensionSpec("quality", "alias")))
+        .setDimFilter(new JavaScriptDimFilter("quality", "function(dim){ return true; }"))
+        .setAggregatorSpecs(
+            Arrays.asList(
+                QueryRunnerTestHelper.rowsCount,
+                new LongSumAggregatorFactory("idx", "index")
+            )
+        )
+        .setGranularity(QueryRunnerTestHelper.dayGran)
+        .build();
+
+    GroupByQuery query = GroupByQuery
+        .builder()
+        .setDataSource(subquery)
+        .setQuerySegmentSpec(
+            new MultipleIntervalSegmentSpec(
+                ImmutableList.of(
+                    new Interval("2011-04-01T00:00:00.000Z/2011-04-03T00:00:00.000Z")
+                )
+            )
+        )
+        .setDimensions(Lists.<DimensionSpec>newArrayList(
+                           new ExtractionDimensionSpec(
+                               "alias",
+                               "alias",
+                               new RegexDimExtractionFn("(a).*", true, "a")
+                           )
+                       )
+        )
+        .setAggregatorSpecs(
+            Arrays.<AggregatorFactory>asList(
+                new LongSumAggregatorFactory("rows", "rows"),
+                new LongSumAggregatorFactory("idx", "idx")
+            )
+        )
+        .setGranularity(QueryRunnerTestHelper.dayGran)
+        .build();
+
+    List<Row> expectedResults = Arrays.asList(
+        GroupByQueryRunnerTestHelper.createExpectedRow("2011-04-01", "alias", "a", "rows", 13L, "idx", 6619L),
+        GroupByQueryRunnerTestHelper.createExpectedRow("2011-04-02", "alias", "a", "rows", 13L, "idx", 5827L)
+    );
+
+    // Subqueries are handled by the ToolChest
+    Iterable<Row> results = GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
+    TestHelper.assertExpectedObjects(expectedResults, results, "");
+  }
+
   @Test
   public void testDifferentGroupingSubquery()
   {