diff --git a/dbms/include/DB/Common/HashTable/TwoLevelHashTable.h b/dbms/include/DB/Common/HashTable/TwoLevelHashTable.h
index 2dd99f8cfe02bd0845d7aab5fbfa4082550d8283..916c27b7a156ac11d8e419e316bcbaddc64f85cb 100644
--- a/dbms/include/DB/Common/HashTable/TwoLevelHashTable.h
+++ b/dbms/include/DB/Common/HashTable/TwoLevelHashTable.h
@@ -95,6 +95,7 @@ public:
 	{
 		typename Source::const_iterator it = src.begin();
 
+		/// Предполагается, что нулевой ключ (хранящийся отдельно) при итерировании идёт первым.
 		if (it != src.end() && it.getPtr()->isZero(src))
 		{
 			insert(*it);
@@ -142,6 +143,8 @@ public:
 
 		value_type & operator* () const { return *current_it; }
 		value_type * operator->() const { return &*current_it; }
+
+		Cell * getPtr() const { return current_it.getPtr(); }
 	};
 
 
@@ -177,6 +180,8 @@ public:
 
 		const value_type & operator* () const { return *current_it; }
 		const value_type * operator->() const { return &*current_it; }
+
+		const Cell * getPtr() const { return current_it.getPtr(); }
 	};
 
 
@@ -205,6 +210,10 @@ public:
 
 		std::pair<iterator, bool> res;
 		emplace(Cell::getKey(x), res.first, res.second, hash_value);
+
+		if (res.second)
+			res.first.getPtr()->setMapped(x);
+
 		return res;
 	}
 
diff --git a/dbms/include/DB/Common/VirtualColumnUtils.h b/dbms/include/DB/Common/VirtualColumnUtils.h
index 0d873ce3cbab05628bef62b708daa8ac1cfb197c..a4848d5e17b63a44f3bda0e56498b0def459c73e 100644
--- a/dbms/include/DB/Common/VirtualColumnUtils.h
+++ b/dbms/include/DB/Common/VirtualColumnUtils.h
@@ -1,19 +1,18 @@
 #pragma once
 
-#include <DB/Interpreters/Context.h>
-#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
-#include <DB/DataStreams/OneBlockInputStream.h>
-#include <DB/DataTypes/DataTypeString.h>
-#include <DB/DataTypes/DataTypesNumberFixed.h>
-#include <DB/Parsers/ASTIdentifier.h>
-#include <DB/Parsers/ASTExpressionList.h>
-#include <DB/Parsers/ASTLiteral.h>
-#include <DB/Parsers/ASTSelectQuery.h>
-#include <DB/Columns/ColumnString.h>
+#include <set>
+
+#include <DB/Core/Block.h>
+#include <DB/Core/NamesAndTypes.h>
+#include <DB/Parsers/IAST.h>
+
 
 namespace DB
 {
 
+class Context;
+
+
 namespace VirtualColumnUtils
 {
 
diff --git a/dbms/include/DB/DataStreams/RemoteBlockInputStream.h b/dbms/include/DB/DataStreams/RemoteBlockInputStream.h
index 8efbf9dfae59efd58f519bbc23e33d6f45eb5709..d31f1e68ea7e52856990880af08733b0bfcf1536 100644
--- a/dbms/include/DB/DataStreams/RemoteBlockInputStream.h
+++ b/dbms/include/DB/DataStreams/RemoteBlockInputStream.h
@@ -3,7 +3,9 @@
 #include <Yandex/logger_useful.h>
 
 #include <DB/DataStreams/IProfilingBlockInputStream.h>
+#include <DB/DataStreams/OneBlockInputStream.h>
 #include <DB/Common/VirtualColumnUtils.h>
+#include <DB/Interpreters/Context.h>
 
 #include <DB/Client/ConnectionPool.h>
 
diff --git a/dbms/include/DB/Interpreters/AggregationCommon.h b/dbms/include/DB/Interpreters/AggregationCommon.h
index 5d06d11c03a774ae77344ae219735f2c951a3b6f..23c092da299845081c0a7b944a7efe822fb958d6 100644
--- a/dbms/include/DB/Interpreters/AggregationCommon.h
+++ b/dbms/include/DB/Interpreters/AggregationCommon.h
@@ -9,8 +9,6 @@
 #include <DB/Core/Defines.h>
 #include <DB/Core/StringRef.h>
 #include <DB/Columns/IColumn.h>
-#include <DB/Common/HashTable/HashMap.h>
-#include <DB/Common/HashTable/TwoLevelHashMap.h>
 
 
 template <>
diff --git a/dbms/include/DB/Interpreters/Aggregator.h b/dbms/include/DB/Interpreters/Aggregator.h
index a1e2213d52cec37f981be218228ff61b8d80b59c..f45c30a6c55809f926f115178db3b904aa2ee49a 100644
--- a/dbms/include/DB/Interpreters/Aggregator.h
+++ b/dbms/include/DB/Interpreters/Aggregator.h
@@ -7,6 +7,8 @@
 
 #include <DB/Core/StringRef.h>
 #include <DB/Common/Arena.h>
+#include <DB/Common/HashTable/HashMap.h>
+#include <DB/Common/HashTable/TwoLevelHashMap.h>
 
 #include <DB/DataStreams/IBlockInputStream.h>
 
diff --git a/dbms/src/Common/VirtualColumnUtils.cpp b/dbms/src/Common/VirtualColumnUtils.cpp
index bec2bca6787116ced35662e16f1f765b8a8c9def..d7d69eaa293b540081d89f6ea47618bcb05ceeca 100644
--- a/dbms/src/Common/VirtualColumnUtils.cpp
+++ b/dbms/src/Common/VirtualColumnUtils.cpp
@@ -1,16 +1,12 @@
-#include <DB/Common/VirtualColumnUtils.h>
-
 #include <DB/Interpreters/Context.h>
-#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
-#include <DB/DataStreams/OneBlockInputStream.h>
-#include <DB/DataTypes/DataTypeString.h>
-#include <DB/DataTypes/DataTypesNumberFixed.h>
+#include <DB/Interpreters/ExpressionAnalyzer.h>
 #include <DB/Parsers/ASTIdentifier.h>
 #include <DB/Parsers/ASTExpressionList.h>
 #include <DB/Parsers/ASTLiteral.h>
 #include <DB/Parsers/ASTSelectQuery.h>
-#include <DB/Storages/IStorage.h>
-#include <DB/Interpreters/InterpreterSelectQuery.h>
+
+#include <DB/Common/VirtualColumnUtils.h>
+
 
 namespace DB
 {
diff --git a/dbms/src/Interpreters/Aggregator.cpp b/dbms/src/Interpreters/Aggregator.cpp
index a7dd3973a21c1d66735368e87430364adaab8787..35cbfbaaf36ff3dae9b9c34ffcab16876513b2d3 100644
--- a/dbms/src/Interpreters/Aggregator.cpp
+++ b/dbms/src/Interpreters/Aggregator.cpp
@@ -442,10 +442,7 @@ void NO_INLINE Aggregator::mergeTwoLevelDataImpl(
 		}
 	};
 
-	/// future и packaged_task используются, чтобы исключения автоматически прокидывались в основной поток.
-
-	std::vector<std::future<void>> futures;
-	futures.reserve(Method::Data::NUM_BUCKETS);
+	/// packaged_task используются, чтобы исключения автоматически прокидывались в основной поток.
 
 	std::vector<std::packaged_task<void()>> tasks;
 	tasks.reserve(Method::Data::NUM_BUCKETS);
@@ -453,7 +450,6 @@ void NO_INLINE Aggregator::mergeTwoLevelDataImpl(
 	for (size_t bucket = 0; bucket < Method::Data::NUM_BUCKETS; ++bucket)
 	{
 		tasks.emplace_back(std::bind(merge_bucket, bucket, current_memory_tracker));
-		futures.emplace_back(tasks.back().get_future());
 
 		if (thread_pool)
 			thread_pool->schedule([bucket, &tasks] { tasks[bucket](); });
@@ -464,8 +460,8 @@ void NO_INLINE Aggregator::mergeTwoLevelDataImpl(
 	if (thread_pool)
 		thread_pool->wait();
 
-	for (auto & future : futures)
-		future.get();
+	for (auto & task : tasks)
+		task.get_future().get();
 }
 
 
@@ -635,16 +631,17 @@ bool Aggregator::executeOnBlock(Block & block, AggregatedDataVariants & result,
 	/** Почему выбрано 30 000? Потому что при таком количестве элементов, в TwoLevelHashTable,
 	  *  скорее всего, хватит места на все ключи, с размером таблицы по-умолчанию
 	  *  (256 корзин по 256 ячеек, fill factor = 0.5)
+	  * TODO Не конвертировать, если запрос выполняется в один поток.
 	  */
 
 	if (result.isConvertibleToTwoLevel() && result_size >= TWO_LEVEL_HASH_TABLE_THRESHOLD)
 		result.convertToTwoLevel();
 
 	/// Проверка ограничений.
-	if (!no_more_keys && max_rows_to_group_by && result.size() > max_rows_to_group_by)
+	if (!no_more_keys && max_rows_to_group_by && result_size > max_rows_to_group_by)
 	{
 		if (group_by_overflow_mode == OverflowMode::THROW)
-			throw Exception("Limit for rows to GROUP BY exceeded: has " + toString(result.size())
+			throw Exception("Limit for rows to GROUP BY exceeded: has " + toString(result_size)
 				+ " rows, maximum: " + toString(max_rows_to_group_by),
 				ErrorCodes::TOO_MUCH_ROWS);
 		else if (group_by_overflow_mode == OverflowMode::BREAK)
diff --git a/dbms/src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp b/dbms/src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp
index e2367f44dcb4fd5f4b2532a32e2777fcfe21ed9f..df0175ef9251e0ad8fdf44444137071711cdd9d0 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp
@@ -6,6 +6,7 @@
 #include <DB/DataStreams/FilterBlockInputStream.h>
 #include <DB/DataStreams/ConcatBlockInputStream.h>
 #include <DB/DataStreams/CollapsingFinalBlockInputStream.h>
+#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
 #include <DB/DataTypes/DataTypesNumberFixed.h>
 #include <DB/Common/VirtualColumnUtils.h>
 
diff --git a/dbms/src/Storages/StorageChunkMerger.cpp b/dbms/src/Storages/StorageChunkMerger.cpp
index 7462efa9f206a6b163726abc9a346f014d9065a5..0c3b66615d7b46ff557bcfb714fc9d539a339233 100644
--- a/dbms/src/Storages/StorageChunkMerger.cpp
+++ b/dbms/src/Storages/StorageChunkMerger.cpp
@@ -14,7 +14,10 @@
 #include <DB/DataStreams/ConcatBlockInputStream.h>
 #include <DB/DataStreams/narrowBlockInputStreams.h>
 #include <DB/DataStreams/AddingDefaultBlockInputStream.h>
+#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
 #include <DB/Common/VirtualColumnUtils.h>
+#include <DB/DataTypes/DataTypeString.h>
+#include <DB/Columns/ColumnString.h>
 
 
 namespace DB
diff --git a/dbms/src/Storages/StorageChunks.cpp b/dbms/src/Storages/StorageChunks.cpp
index c3aad961a39532b01b1a87fc56e5e9d7370df272..6617e1788eb07028727868e78cf943956f435809 100644
--- a/dbms/src/Storages/StorageChunks.cpp
+++ b/dbms/src/Storages/StorageChunks.cpp
@@ -6,6 +6,8 @@
 #include <DB/Interpreters/InterpreterDropQuery.h>
 #include <DB/Parsers/ASTDropQuery.h>
 #include <DB/Common/VirtualColumnUtils.h>
+#include <DB/DataTypes/DataTypeString.h>
+#include <DB/Columns/ColumnString.h>
 
 
 namespace DB
diff --git a/dbms/src/Storages/StorageMerge.cpp b/dbms/src/Storages/StorageMerge.cpp
index fcb99636408438bd2a2605efc992883b84d39c3c..309826e9059cb7a18b1d1cc332a0a0dd4ea70c14 100644
--- a/dbms/src/Storages/StorageMerge.cpp
+++ b/dbms/src/Storages/StorageMerge.cpp
@@ -1,8 +1,13 @@
 #include <DB/DataStreams/narrowBlockInputStreams.h>
+#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
 #include <DB/Storages/StorageMerge.h>
 #include <DB/Common/VirtualColumnUtils.h>
 #include <DB/Interpreters/InterpreterAlterQuery.h>
 #include <DB/Storages/VirtualColumnFactory.h>
+#include <DB/Parsers/ASTSelectQuery.h>
+#include <DB/DataTypes/DataTypeString.h>
+#include <DB/Columns/ColumnString.h>
+
 
 namespace DB
 {
diff --git a/dbms/src/Storages/StorageReplicatedMergeTree.cpp b/dbms/src/Storages/StorageReplicatedMergeTree.cpp
index 8f669e5d25d275be4f0346111a7f864e18c8f6c5..715aabf6011dbbb1ea525fc5527739d1658b597c 100644
--- a/dbms/src/Storages/StorageReplicatedMergeTree.cpp
+++ b/dbms/src/Storages/StorageReplicatedMergeTree.cpp
@@ -8,8 +8,10 @@
 #include <DB/IO/ReadBufferFromString.h>
 #include <DB/Interpreters/InterpreterAlterQuery.h>
 #include <DB/Common/VirtualColumnUtils.h>
+#include <DB/DataStreams/AddingConstColumnBlockInputStream.h>
 #include <time.h>
 
+
 namespace DB
 {