**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

class IMergeTreeDataPartWriter;
class MarkCache;
class UncompressedCache;
namespace ErrorCodes
{
}
class IMergeTreeDataPart : public std::enable_shared_from_this<IMergeTreeDataPart>
{
public:
    using Checksums = MergeTreeDataPartChecksums;
    using Checksum = MergeTreeDataPartChecksums::Checksum;
    using ValueSizeMap = std::map<std::string, double>;
    using MergeTreeReaderPtr = std::unique_ptr<IMergeTreeReader>;
    using MergeTreeWriterPtr = std::unique_ptr<IMergeTreeDataPartWriter>;
    using ColumnSizeByName = std::unordered_map<std::string, ColumnSize>;
    using NameToPosition = std::unordered_map<std::string, size_t>;
    using Type = MergeTreeDataPartType;
    IMergeTreeDataPart(
        const MergeTreeData & storage_,
        const String & name_,
        const MergeTreePartInfo & info_,
        const VolumePtr & volume,
        const std::optional<String> & relative_path,
        Type part_type_);
    IMergeTreeDataPart(
        MergeTreeData & storage_,
        const String & name_,
        const VolumePtr & volume,
        const std::optional<String> & relative_path,