**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

Type part_type_);
    virtual MergeTreeReaderPtr getReader(
        const NamesAndTypesList & columns_,
        const StorageMetadataPtr & metadata_snapshot,
        const MarkRanges & mark_ranges,
        UncompressedCache * uncompressed_cache,
        MarkCache * mark_cache,
        const MergeTreeReaderSettings & reader_settings_,
        const ValueSizeMap & avg_value_size_hints_ = ValueSizeMap{},
        const ReadBufferFromFileBase::ProfileCallback & profile_callback_ = ReadBufferFromFileBase::ProfileCallback{}) const = 0;
    virtual MergeTreeWriterPtr getWriter(
        const NamesAndTypesList & columns_list,
        const StorageMetadataPtr & metadata_snapshot,
        const std::vector<MergeTreeIndexPtr> & indices_to_recalc,
        const CompressionCodecPtr & default_codec_,
        const MergeTreeWriterSettings & writer_settings,
        const MergeTreeIndexGranularity & computed_index_granularity = {}) const = 0;
    virtual bool isStoredOnDisk() const = 0;
    virtual bool supportsVerticalMerge() const { return false; }
    
    
    ColumnSize getColumnSize(const String & column_name, const IDataType & ) const;
    
    ColumnSize getTotalColumnsSize() const { return total_columns_size; }
    virtual String getFileNameForColumn(const NameAndTypePair & column) const = 0;
    virtual ~IMergeTreeDataPart();
    using ColumnToSize = std::map<std::string, UInt64>;
    
    void accumulateColumnSizes(ColumnToSize & ) const;
    Type getType() const { return part_type; }