**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

MergeTreeDataPartType type, const MergeTreePartInfo & part_info,
    const VolumePtr & volume, const String & relative_path) const
{
    if (type == MergeTreeDataPartType::COMPACT)
        return std::make_shared<MergeTreeDataPartCompact>(*this, name, part_info, volume, relative_path);
    else if (type == MergeTreeDataPartType::WIDE)
        return std::make_shared<MergeTreeDataPartWide>(*this, name, part_info, volume, relative_path);
    else if (type == MergeTreeDataPartType::IN_MEMORY)
        return std::make_shared<MergeTreeDataPartInMemory>(*this, name, part_info, volume, relative_path);
    else
        throw Exception("Unknown type of part " + relative_path, ErrorCodes::UNKNOWN_PART_TYPE);
}
static MergeTreeDataPartType getPartTypeFromMarkExtension(const String & mrk_ext)
{
    if (mrk_ext == getNonAdaptiveMrkExtension())
        return MergeTreeDataPartType::WIDE;
    if (mrk_ext == getAdaptiveMrkExtension(MergeTreeDataPartType::WIDE))
        return MergeTreeDataPartType::WIDE;
    if (mrk_ext == getAdaptiveMrkExtension(MergeTreeDataPartType::COMPACT))
        return MergeTreeDataPartType::COMPACT;
    throw Exception("Can't determine part type, because of unknown mark extension " + mrk_ext, ErrorCodes::UNKNOWN_PART_TYPE);
}
MergeTreeData::MutableDataPartPtr MergeTreeData::createPart(