```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 (totals_having_port)
        throw Exception("Totals having transform was already added to pipeline.", ErrorCodes::LOGICAL_ERROR);
    checkSource(source, false);
    assertBlocksHaveEqualStructure(current_header, source->getOutputs().front().getHeader(), "QueryPipeline");
    totals_having_port = &source->getOutputs().front();
    processors.emplace(std::move(source));
}
void QueryPipeline::dropTotalsAndExtremes()
{
    auto drop_port = [&](OutputPort *& port)
    {
        auto null_sink = std::make_shared<NullSink>(port->getHeader());
        connect(*port, null_sink->getPort());
        processors.emplace(std::move(null_sink));
        port = nullptr;
    };
    if (totals_having_port)
        drop_port(totals_having_port);
    if (extremes_port)
        drop_port(extremes_port);
}
void QueryPipeline::addExtremesTransform()