**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

for (auto disk_it = disks.rbegin(); disk_it != disks.rend(); ++disk_it)
    {
        auto disk_ptr = *disk_it;
        for (auto it = disk_ptr->iterateDirectory(relative_data_path); it->isValid(); it->next())
        {
            
            if (startsWith(it->name(), "tmp") || it->name() == MergeTreeData::FORMAT_VERSION_FILE_NAME || it->name() == MergeTreeData::DETACHED_DIR_NAME)
                continue;
            if (!startsWith(it->name(), MergeTreeWriteAheadLog::WAL_FILE_NAME))
                part_names_with_disks.emplace_back(it->name(), disk_ptr);
            else if (it->name() == MergeTreeWriteAheadLog::DEFAULT_WAL_FILE_NAME && settings->in_memory_parts_enable_wal)
            {
                
                write_ahead_log = std::make_shared<MergeTreeWriteAheadLog>(*this, disk_ptr, it->name());
                for (auto && part : write_ahead_log->restore(metadata_snapshot))
                    parts_from_wal.push_back(std::move(part));
            }
            else if (settings->in_memory_parts_enable_wal)
            {
                MergeTreeWriteAheadLog wal(*this, disk_ptr, it->name());
                for (auto && part : wal.restore(metadata_snapshot))
                    parts_from_wal.push_back(std::move(part));
            }
        }
    }
    auto part_lock = lockParts();
    data_parts_indexes.clear();
    if (part_names_with_disks.empty() && parts_from_wal.empty())
    {
        LOG_DEBUG(log, "There is no data parts");