**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

{
    return NamesAndTypesList{
        NameAndTypePair("_part", std::make_shared<DataTypeString>()),
        NameAndTypePair("_part_index", std::make_shared<DataTypeUInt64>()),
        NameAndTypePair("_part_uuid", std::make_shared<DataTypeUUID>()),
        NameAndTypePair("_partition_id", std::make_shared<DataTypeString>()),
        NameAndTypePair("_sample_factor", std::make_shared<DataTypeFloat64>()),
    };
}
size_t MergeTreeData::getTotalMergesWithTTLInMergeList() const
{
    return global_context.getMergeList().getMergesWithTTLCount();
}
void MergeTreeData::addPartContributionToDataVolume(const DataPartPtr & part)
{
    increaseDataVolume(part->getBytesOnDisk(), part->rows_count, 1);
}
void MergeTreeData::removePartContributionToDataVolume(const DataPartPtr & part)
{
    decreaseDataVolume(part->getBytesOnDisk(), part->rows_count, 1);
}
void MergeTreeData::increaseDataVolume(size_t bytes, size_t rows, size_t parts)