```sql
SELECT count()
FROM 
(
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
    UNION ALL
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
    UNION ALL
    SELECT number
    FROM numbers_mt(100000000)
    ORDER BY number DESC
    LIMIT 100
)


SET experimental_use_processors = 0;
-- 1 rows in set. Elapsed: 1.581 sec. Processed 300.00 million rows, 2.40 GB (189.78 million rows/s., 1.52 GB/s.) 

SET experimental_use_processors = 1;
-- 1 rows in set. Elapsed: 3.569 sec. Processed 300.00 million rows, 2.40 GB (84.06 million rows/s., 672.50 MB/s.) 
```

Similar for MergeTree:

```sql
create table test engine=MergeTree order by tuple() as select * from numbers(30000000);

select count() from (select number from test group by number order by number limit 10 union all select number from test group by number order by number limit 10);

set experimental_use_processors=0;
-- Elapsed: 2.664 sec

set experimental_use_processors=1;
-- Elapsed: 3.656 sec
```
#include <Processors/QueryPipeline.h>
#include <Processors/ResizeProcessor.h>
#include <Processors/ConcatProcessor.h>
#include <Processors/NullSink.h>
#include <Processors/LimitTransform.h>
#include <Processors/Sources/NullSource.h>
#include <Processors/Transforms/TotalsHavingTransform.h>
#include <Processors/Transforms/ExtremesTransform.h>
#include <Processors/Transforms/CreatingSetsTransform.h>
#include <Processors/Transforms/ConvertingTransform.h>
#include <Processors/Formats/IOutputFormat.h>
#include <Processors/Sources/SourceFromInputStream.h>
#include <Processors/Executors/PipelineExecutor.h>
#include <Processors/Transforms/PartialSortingTransform.h>
#include <Processors/Sources/SourceFromSingleChunk.h>
#include <IO/WriteHelpers.h>
#include <Interpreters/Context.h>
#include <Common/typeid_cast.h>
#include <Common/CurrentThread.h>
#include <Processors/DelayedPortsProcessor.h>
#include <Processors/RowsBeforeLimitCounter.h>
#include <Processors/Sources/RemoteSource.h>
namespace DB
{
namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
}
void QueryPipeline::checkInitialized()