**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 StorageID & table_id_,
    const String & relative_data_path_,
    const StorageInMemoryMetadata & metadata_,
    Context & context_,
    const String & date_column_name,
    const MergingParams & merging_params_,
    std::unique_ptr<MergeTreeSettings> storage_settings_,
    bool require_part_metadata_,
    bool attach,
    BrokenPartCallback broken_part_callback_)
    : IStorage(table_id_)
    , global_context(context_.getGlobalContext())
    , merging_params(merging_params_)
    , require_part_metadata(require_part_metadata_)
    , relative_data_path(relative_data_path_)
    , broken_part_callback(broken_part_callback_)
    , log_name(table_id_.getNameForLogs())
    , log(&Poco::Logger::get(log_name))
    , storage_settings(std::move(storage_settings_))
    , data_parts_by_info(data_parts_indexes.get<TagByInfo>())
    , data_parts_by_state_and_info(data_parts_indexes.get<TagByStateAndInfo>())
    , parts_mover(this)
{
    const auto settings = getSettings();
    allow_nullable_key = attach || settings->allow_nullable_key;