**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

{
            
            if (committed_big_parts_from_partition.find(name) == committed_big_parts_from_partition.end()
                && part_info.partition_id == emerging_part.partition_id)
            {
                auto it = disk_occupation.find(emerging_part.disk_name);
                if (it != disk_occupation.end())
                {
                    it->second += emerging_part.estimate_bytes;
                    disk_parts_for_logging[emerging_part.disk_name].push_back(
                        formatReadableSizeWithBinarySuffix(emerging_part.estimate_bytes) + " (emerging)");
                }
                else
                {
                    
                }
            }
        }
        size_t min_occupation_size = std::numeric_limits<size_t>::max();
        std::vector<String> candidates;
        for (const auto & [disk_name, size] : disk_occupation)
        {
            if (size < min_occupation_size)
            {
                min_occupation_size = size;
                candidates = {disk_name};
            }
            else if (size == min_occupation_size)
            {
                candidates.push_back(disk_name);