**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

all_diff_disk_names.erase(disk->getName());
                    for (const String & disk_name : all_diff_disk_names)
                    {
                        auto disk = new_storage_policy->getDiskByName(disk_name);
                        if (disk->exists(relative_data_path))
                            throw Exception("New storage policy contain disks which already contain data of a table with the same name", ErrorCodes::LOGICAL_ERROR);
                    }
                    for (const String & disk_name : all_diff_disk_names)
                    {
                        auto disk = new_storage_policy->getDiskByName(disk_name);
                        disk->createDirectories(relative_data_path);
                        disk->createDirectories(relative_data_path + MergeTreeData::DETACHED_DIR_NAME);
                    }
                    
                    has_storage_policy_changed = true;
                }
            }
        }
        MergeTreeSettings copy = *getSettings();
        copy.applyChanges(new_changes);
        copy.sanityCheck(global_context.getSettingsRef());
        storage_settings.set(std::make_unique<const MergeTreeSettings>(copy));
        StorageInMemoryMetadata new_metadata = getInMemoryMetadata();
        new_metadata.setSettingsChanges(new_settings);
        setInMemoryMetadata(new_metadata);
        if (has_storage_policy_changed)
            startBackgroundMovesIfNeeded();
    }
}
void MergeTreeData::PartsTemporaryRename::addPart(const String & old_name, const String & new_name)