```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
```
{
    checkInitializedAndNotCompleted();
    if (!typeid_cast<const CreatingSetsTransform *>(transform.get()))
        throw Exception("CreatingSetsTransform expected for QueryPipeline::addExtremesTransform.",
                        ErrorCodes::LOGICAL_ERROR);
    resize(1);
    auto concat = std::make_shared<ConcatProcessor>(current_header, 2);
    connect(transform->getOutputs().front(), concat->getInputs().front());
    connect(*streams.back(), concat->getInputs().back());
    streams.assign({ &concat->getOutputs().front() });
    processors.emplace(std::move(transform));
    processors.emplace(std::move(concat));
}
void QueryPipeline::setOutputFormat(ProcessorPtr output)