**Describe the bug**

I have a table like:

```
CREATE TABLE test (
    time DateTime64(3)
    ...
) ENGINE = MergeTree()
PARTITION BY toStartOfInterval(time, INTERVAL 1 HOUR)
...
```

But when I search in `system.parts` it does not appear to have the `min/max` columns appropriately set?

```
partition:                             2020-06-01 01:00:00
min_date:                              1970-01-01
max_date:                              1970-01-01
min_time:                              1970-01-01 00:00:00
max_time:                              1970-01-01 00:00:00
```

I assume that if these were correctly set, doing a `select toStartOfInterval(time, interval 1 day), count()` type query would be pretty instant rather than trying to scan everything? I am guessing this is due to the `DateTime64` type in use?

Clickhouse 20.11.3.3

}
    auto is_range_on_disk = [&block_numbers_on_disk](Int64 min_block, Int64 max_block)
    {
        auto lower = std::lower_bound(block_numbers_on_disk.begin(), block_numbers_on_disk.end(), std::make_pair(min_block, Int64(-1L)));
        if (lower != block_numbers_on_disk.end() && min_block >= lower->first && max_block <= lower->second)
            return true;
        if (lower != block_numbers_on_disk.begin())
        {
            --lower;
            if (min_block >= lower->first && max_block <= lower->second)
                return true;
        }
        return false;
    };
    auto disks = getStoragePolicy()->getDisks();
    for (auto disk_it = disks.rbegin(); disk_it != disks.rend(); ++disk_it)
    {
        auto disk_ptr = *disk_it;
        for (auto it = disk_ptr->iterateDirectory(relative_data_path); it->isValid(); it->next())
        {
            auto min_max_block_number = MergeTreeWriteAheadLog::tryParseMinMaxBlockNumber(it->name());
            if (min_max_block_number && is_range_on_disk(min_max_block_number->first, min_max_block_number->second))
            {
                LOG_DEBUG(log, "Removing from filesystem the outdated WAL file " + it->name());
                disk_ptr->removeFile(relative_data_path + it->name());
            }
        }
    }
}
void MergeTreeData::clearEmptyParts()