**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

}
    }
}
MergeTreeData::DataPartsVector MergeTreeData::grabOldParts(bool force)
{
    DataPartsVector res;
    
    std::unique_lock lock(grab_old_parts_mutex, std::defer_lock);
    if (!lock.try_lock())
        return res;
    time_t now = time(nullptr);
    std::vector<DataPartIteratorByStateAndInfo> parts_to_delete;
    {
        auto parts_lock = lockParts();
        auto outdated_parts_range = getDataPartsStateRange(DataPartState::Outdated);
        for (auto it = outdated_parts_range.begin(); it != outdated_parts_range.end(); ++it)
        {
            const DataPartPtr & part = *it;
            auto part_remove_time = part->remove_time.load(std::memory_order_relaxed);
            if (part.unique() && 
                ((part_remove_time < now &&
                now - part_remove_time > getSettings()->old_parts_lifetime.totalSeconds()) || force
                || isInMemoryPart(part))) 
            {
                parts_to_delete.emplace_back(it);
            }
        }
        res.reserve(parts_to_delete.size());
        for (const auto & it_to_delete : parts_to_delete)
        {