21.7.3 throws an exception if `_sample_factor` is used in a query:
```
CREATE TABLE sessions
(
  `user_id` UInt64
)
ENGINE = MergeTree
ORDER BY user_id 
SAMPLE BY user_id;

insert into sessions values(1);

SELECT
    sum(user_id * _sample_factor) 
FROM sessions
SAMPLE 10000000

DB::Exception: Cannot find column `user_id` in source stream (version 21.8.1.7409 (official build))

SELECT
    sum(user_id) 
FROM sessions
SAMPLE 10000000

sum(user_id)
------------
           1
```
No exception on 21.6.5
format_settings.out << prefix << indent << indent << "Keys: " << stat.name << '\n';
                for (const auto & used_key : stat.used_keys)
                    format_settings.out << prefix << indent << indent << indent << used_key << '\n';
            }
            if (!stat.condition.empty())
                format_settings.out << prefix << indent << indent << "Condition: " << stat.condition << '\n';
            format_settings.out << prefix << indent << indent << "Parts: " << stat.num_parts_after;
            if (i)
                format_settings.out << '/' << index_stats[i - 1].num_parts_after;
            format_settings.out << '\n';
            format_settings.out << prefix << indent << indent << "Granules: " << stat.num_granules_after;
            if (i)
                format_settings.out << '/' << index_stats[i - 1].num_granules_after;
            format_settings.out << '\n';
        }
    }
}
void ReadFromMergeTree::describeIndexes(JSONBuilder::JSONMap & map) const
{
    auto result = selectRangesToRead(prepared_parts);
    auto index_stats = std::move(result.index_stats);
    if (!index_stats.empty())
    {
        
        if (index_stats.size() == 1 && index_stats.front().type == IndexType::None)
            return;
        auto indexes_array = std::make_unique<JSONBuilder::JSONArray>();
        for (size_t i = 0; i < index_stats.size(); ++i)
        {
            const auto & stat = index_stats[i];