diff --git a/processing/src/main/java/io/druid/query/QueryToolChest.java b/processing/src/main/java/io/druid/query/QueryToolChest.java
index 7d42eda6792..fb8c73bb4c6 100644
--- a/processing/src/main/java/io/druid/query/QueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/QueryToolChest.java
@@ -46,6 +46,9 @@ public abstract class QueryToolChest<ResultType, QueryType extends Query<ResultT
    */
   public abstract Sequence<ResultType> mergeSequences(Sequence<Sequence<ResultType>> seqOfSequences);
 
+  public abstract Sequence<ResultType> mergeSequencesUnordered(Sequence<Sequence<ResultType>> seqOfSequences);
+
+
   public abstract ServiceMetricEvent.Builder makeMetricBuilder(QueryType query);
 
   public abstract Function<ResultType, ResultType> makePreComputeManipulatorFn(
diff --git a/processing/src/main/java/io/druid/query/UnionQueryRunner.java b/processing/src/main/java/io/druid/query/UnionQueryRunner.java
index 2610cdfc20e..f14bb180f62 100644
--- a/processing/src/main/java/io/druid/query/UnionQueryRunner.java
+++ b/processing/src/main/java/io/druid/query/UnionQueryRunner.java
@@ -45,7 +45,7 @@ public class UnionQueryRunner<T> implements QueryRunner<T>
   {
     DataSource dataSource = query.getDataSource();
     if (dataSource instanceof UnionDataSource) {
-      return toolChest.mergeSequences(
+      return toolChest.mergeSequencesUnordered(
           Sequences.simple(
               Lists.transform(
                   ((UnionDataSource) dataSource).getDataSources(),
diff --git a/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
index 123bd230287..e2ddc18da5c 100644
--- a/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/groupby/GroupByQueryQueryToolChest.java
@@ -193,7 +193,18 @@ public class GroupByQueryQueryToolChest extends QueryToolChest<Row, GroupByQuery
   @Override
   public Sequence<Row> mergeSequences(Sequence<Sequence<Row>> seqOfSequences)
   {
-    return new OrderedMergeSequence<>(Ordering.<Row>natural().nullsFirst(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<Row> mergeSequencesUnordered(Sequence<Sequence<Row>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  private Ordering<Row> getOrdering()
+  {
+    return Ordering.<Row>natural().nullsFirst();
   }
 
   @Override
@@ -372,7 +383,7 @@ public class GroupByQueryQueryToolChest extends QueryToolChest<Row, GroupByQuery
       @Override
       public Sequence<Row> mergeSequences(Sequence<Sequence<Row>> seqOfSequences)
       {
-        return new MergeSequence<>(Ordering.<Row>natural().nullsFirst(), seqOfSequences);
+        return new MergeSequence<>(getOrdering(), seqOfSequences);
       }
     };
   }
diff --git a/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
index f21665b1a38..21f02145988 100644
--- a/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java
@@ -146,7 +146,13 @@ public class SegmentMetadataQueryQueryToolChest extends QueryToolChest<SegmentAn
   @Override
   public Sequence<SegmentAnalysis> mergeSequences(Sequence<Sequence<SegmentAnalysis>> seqOfSequences)
   {
-    return new OrderedMergeSequence<SegmentAnalysis>(getOrdering(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<SegmentAnalysis> mergeSequencesUnordered(Sequence<Sequence<SegmentAnalysis>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
index e24239f8896..558d7ee3f13 100644
--- a/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/search/SearchQueryQueryToolChest.java
@@ -111,7 +111,13 @@ public class SearchQueryQueryToolChest extends QueryToolChest<Result<SearchResul
   @Override
   public Sequence<Result<SearchResultValue>> mergeSequences(Sequence<Sequence<Result<SearchResultValue>>> seqOfSequences)
   {
-    return new OrderedMergeSequence<Result<SearchResultValue>>(getOrdering(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<Result<SearchResultValue>> mergeSequencesUnordered(Sequence<Sequence<Result<SearchResultValue>>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
index 95480302336..345aeff1d5b 100644
--- a/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/select/SelectQueryQueryToolChest.java
@@ -113,7 +113,13 @@ public class SelectQueryQueryToolChest extends QueryToolChest<Result<SelectResul
   @Override
   public Sequence<Result<SelectResultValue>> mergeSequences(Sequence<Sequence<Result<SelectResultValue>>> seqOfSequences)
   {
-    return new OrderedMergeSequence<Result<SelectResultValue>>(getOrdering(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<Result<SelectResultValue>> mergeSequencesUnordered(Sequence<Sequence<Result<SelectResultValue>>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
index 6e0f41db855..a45a63e031d 100644
--- a/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/timeboundary/TimeBoundaryQueryQueryToolChest.java
@@ -113,6 +113,12 @@ public class TimeBoundaryQueryQueryToolChest
     return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
   }
 
+  @Override
+  public Sequence<Result<TimeBoundaryResultValue>> mergeSequencesUnordered(Sequence<Sequence<Result<TimeBoundaryResultValue>>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
   @Override
   public ServiceMetricEvent.Builder makeMetricBuilder(TimeBoundaryQuery query)
   {
diff --git a/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
index e7c7e0849b5..3ed7e84149d 100644
--- a/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/timeseries/TimeseriesQueryQueryToolChest.java
@@ -112,7 +112,13 @@ public class TimeseriesQueryQueryToolChest extends QueryToolChest<Result<Timeser
   @Override
   public Sequence<Result<TimeseriesResultValue>> mergeSequences(Sequence<Sequence<Result<TimeseriesResultValue>>> seqOfSequences)
   {
-    return new OrderedMergeSequence<Result<TimeseriesResultValue>>(getOrdering(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<Result<TimeseriesResultValue>> mergeSequencesUnordered(Sequence<Sequence<Result<TimeseriesResultValue>>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
   }
 
   @Override
diff --git a/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java b/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
index ab1faebf67e..cc00ea3292e 100644
--- a/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
+++ b/processing/src/main/java/io/druid/query/topn/TopNQueryQueryToolChest.java
@@ -72,7 +72,6 @@ public class TopNQueryQueryToolChest extends QueryToolChest<Result<TopNResultVal
   private static final TypeReference<Object> OBJECT_TYPE_REFERENCE = new TypeReference<Object>()
   {
   };
-
   private final TopNQueryConfig config;
 
   @Inject
@@ -128,7 +127,13 @@ public class TopNQueryQueryToolChest extends QueryToolChest<Result<TopNResultVal
   @Override
   public Sequence<Result<TopNResultValue>> mergeSequences(Sequence<Sequence<Result<TopNResultValue>>> seqOfSequences)
   {
-    return new OrderedMergeSequence<Result<TopNResultValue>>(getOrdering(), seqOfSequences);
+    return new OrderedMergeSequence<>(getOrdering(), seqOfSequences);
+  }
+
+  @Override
+  public Sequence<Result<TopNResultValue>> mergeSequencesUnordered(Sequence<Sequence<Result<TopNResultValue>>> seqOfSequences)
+  {
+    return new MergeSequence<>(getOrdering(), seqOfSequences);
   }
 
   @Override
diff --git a/processing/src/test/java/io/druid/query/timeseries/TimeSeriesUnionQueryRunnerTest.java b/processing/src/test/java/io/druid/query/timeseries/TimeSeriesUnionQueryRunnerTest.java
index 17d61908c3c..84ace0a798f 100644
--- a/processing/src/test/java/io/druid/query/timeseries/TimeSeriesUnionQueryRunnerTest.java
+++ b/processing/src/test/java/io/druid/query/timeseries/TimeSeriesUnionQueryRunnerTest.java
@@ -21,12 +21,18 @@ package io.druid.query.timeseries;
 
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Lists;
+import com.metamx.common.guava.Sequence;
 import com.metamx.common.guava.Sequences;
 import io.druid.query.Druids;
+import io.druid.query.Query;
 import io.druid.query.QueryConfig;
 import io.druid.query.QueryRunner;
 import io.druid.query.QueryRunnerTestHelper;
+import io.druid.query.QueryToolChest;
 import io.druid.query.Result;
+import io.druid.query.TableDataSource;
+import io.druid.query.UnionDataSource;
+import io.druid.query.UnionQueryRunner;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.aggregation.LongSumAggregatorFactory;
 import io.druid.segment.TestHelper;
@@ -43,6 +49,15 @@ import java.util.List;
 @RunWith(Parameterized.class)
 public class TimeSeriesUnionQueryRunnerTest
 {
+  private final QueryRunner runner;
+
+  public TimeSeriesUnionQueryRunnerTest(
+      QueryRunner runner
+  )
+  {
+    this.runner = runner;
+  }
+
   @Parameterized.Parameters
   public static Collection<?> constructorFeeder() throws IOException
   {
@@ -55,15 +70,6 @@ public class TimeSeriesUnionQueryRunnerTest
     );
   }
 
-  private final QueryRunner runner;
-
-  public TimeSeriesUnionQueryRunnerTest(
-      QueryRunner runner
-  )
-  {
-    this.runner = runner;
-  }
-
   @Test
   public void testUnionTimeseries()
   {
@@ -106,6 +112,145 @@ public class TimeSeriesUnionQueryRunnerTest
     TestHelper.assertExpectedResults(expectedResults, results);
   }
 
+  @Test
+  public void testUnionResultMerging()
+  {
+    TimeseriesQuery query = Druids.newTimeseriesQueryBuilder()
+                                  .dataSource(
+                                      new UnionDataSource(
+                                          Lists.newArrayList(
+                                              new TableDataSource("ds1"),
+                                              new TableDataSource("ds2")
+                                          )
+                                      )
+                                  )
+                                  .granularity(QueryRunnerTestHelper.dayGran)
+                                  .intervals(QueryRunnerTestHelper.firstToThird)
+                                  .aggregators(
+                                      Arrays.<AggregatorFactory>asList(
+                                          QueryRunnerTestHelper.rowsCount,
+                                          new LongSumAggregatorFactory(
+                                              "idx",
+                                              "index"
+                                          )
+                                      )
+                                  )
+                                  .build();
+    QueryToolChest toolChest = new TimeseriesQueryQueryToolChest(new QueryConfig());
+    QueryRunner mergingrunner = toolChest.mergeResults(
+        new UnionQueryRunner<Result<TimeseriesResultValue>>(
+            new QueryRunner<Result<TimeseriesResultValue>>()
+            {
+              @Override
+              public Sequence<Result<TimeseriesResultValue>> run(Query<Result<TimeseriesResultValue>> query)
+              {
+                if (query.getDataSource().equals(new TableDataSource("ds1"))) {
+                  return Sequences.simple(
+                      Lists.newArrayList(
+                          new Result<TimeseriesResultValue>(
+                              new DateTime("2011-04-02"),
+                              new TimeseriesResultValue(
+                                  ImmutableMap.<String, Object>of(
+                                      "rows",
+                                      1L,
+                                      "idx",
+                                      2L
+                                  )
+                              )
+                          ),
+                          new Result<TimeseriesResultValue>(
+                              new DateTime("2011-04-03"),
+                              new TimeseriesResultValue(
+                                  ImmutableMap.<String, Object>of(
+                                      "rows",
+                                      3L,
+                                      "idx",
+                                      4L
+                                  )
+                              )
+                          )
+                      )
+                  );
+                } else {
+                  return Sequences.simple(
+                      Lists.newArrayList(
+                          new Result<TimeseriesResultValue>(
+                              new DateTime("2011-04-01"),
+                              new TimeseriesResultValue(
+                                  ImmutableMap.<String, Object>of(
+                                      "rows",
+                                      5L,
+                                      "idx",
+                                      6L
+                                  )
+                              )
+                          ),
+                          new Result<TimeseriesResultValue>(
+                              new DateTime("2011-04-02"),
+                              new TimeseriesResultValue(
+                                  ImmutableMap.<String, Object>of(
+                                      "rows",
+                                      7L,
+                                      "idx",
+                                      8L
+                                  )
+                              )
+                          ),
+                          new Result<TimeseriesResultValue>(
+                              new DateTime("2011-04-04"),
+                              new TimeseriesResultValue(
+                                  ImmutableMap.<String, Object>of(
+                                      "rows",
+                                      9L,
+                                      "idx",
+                                      10L
+                                  )
+                              )
+                          )
+                      )
+                  );
+                }
+              }
+            },
+            toolChest
+        )
+    );
 
+    List<Result<TimeseriesResultValue>> expectedResults = Arrays.asList(
+        new Result<TimeseriesResultValue>(
+            new DateTime("2011-04-01"),
+            new TimeseriesResultValue(
+                ImmutableMap.<String, Object>of("rows", 5L, "idx", 6L)
+            )
+        ),
+        new Result<TimeseriesResultValue>(
+            new DateTime("2011-04-02"),
+            new TimeseriesResultValue(
+                ImmutableMap.<String, Object>of("rows", 8L, "idx", 10L)
+            )
+        ),
+        new Result<TimeseriesResultValue>(
+            new DateTime("2011-04-03"),
+            new TimeseriesResultValue(
+                ImmutableMap.<String, Object>of("rows", 3L, "idx", 4L)
+            )
+        ),
+        new Result<TimeseriesResultValue>(
+            new DateTime("2011-04-04"),
+            new TimeseriesResultValue(
+                ImmutableMap.<String, Object>of("rows", 9L, "idx", 10L)
+            )
+        )
+    );
+
+    Iterable<Result<TimeseriesResultValue>> results = Sequences.toList(
+        mergingrunner.run(query),
+        Lists.<Result<TimeseriesResultValue>>newArrayList()
+    );
+
+    System.out.println(results);
+    TestHelper.assertExpectedResults(expectedResults, results);
+
+  }
 
 }
diff --git a/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java b/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
index 431fdce8318..a8789b021a3 100644
--- a/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
+++ b/server/src/test/java/io/druid/server/coordination/ServerManagerTest.java
@@ -571,6 +571,12 @@ public class ServerManagerTest
       return new ConcatSequence<T>(seqOfSequences);
     }
 
+    @Override
+    public Sequence<T> mergeSequencesUnordered(Sequence<Sequence<T>> seqOfSequences)
+    {
+      return new ConcatSequence<T>(seqOfSequences);
+    }
+
     @Override
     public ServiceMetricEvent.Builder makeMetricBuilder(QueryType query)
     {