**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

{
        const auto & src_relative_data_path = src_part_in_memory->storage.relative_data_path;
        auto flushed_part_path = src_part_in_memory->getRelativePathForPrefix(tmp_part_prefix);
        src_part_in_memory->flushToDisk(src_relative_data_path, flushed_part_path, metadata_snapshot);
        src_part_path = src_relative_data_path + flushed_part_path + "/";
    }
    LOG_DEBUG(log, "Cloning part {} to {}", fullPath(disk, src_part_path), fullPath(disk, dst_part_path));
    localBackup(disk, src_part_path, dst_part_path);
    disk->removeFileIfExists(dst_part_path + "/" + IMergeTreeDataPart::DELETE_ON_DESTROY_MARKER_FILE_NAME);
    auto single_disk_volume = std::make_shared<SingleDiskVolume>(disk->getName(), disk, 0);
    auto dst_data_part = createPart(dst_part_name, dst_part_info, single_disk_volume, tmp_dst_part_name);
    dst_data_part->is_temp = true;
    dst_data_part->loadColumnsChecksumsIndexes(require_part_metadata, true);
    dst_data_part->modification_time = disk->getLastModified(dst_part_path).epochTime();
    return dst_data_part;
}
String MergeTreeData::getFullPathOnDisk(const DiskPtr & disk) const
{
    return disk->getPath() + relative_data_path;
}
DiskPtr MergeTreeData::getDiskForPart(const String & part_name, const String & additional_path) const
{
    const auto disks = getStoragePolicy()->getDisks();
    for (const DiskPtr & disk : disks)
        for (auto it = disk->iterateDirectory(relative_data_path + additional_path); it->isValid(); it->next())
            if (it->name() == part_name)
                return disk;
    return nullptr;
}
std::optional<String> MergeTreeData::getFullRelativePathForPart(const String & part_name, const String & additional_path) const