**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

{
    DataPartsVector parts = getDataPartsVector();
    std::vector<std::pair<Int64, Int64>> all_block_numbers_on_disk;
    std::vector<std::pair<Int64, Int64>> block_numbers_on_disk;
    for (const auto & part : parts)
        if (part->isStoredOnDisk())
            all_block_numbers_on_disk.emplace_back(part->info.min_block, part->info.max_block);
    if (all_block_numbers_on_disk.empty())
        return;
    std::sort(all_block_numbers_on_disk.begin(), all_block_numbers_on_disk.end());
    block_numbers_on_disk.push_back(all_block_numbers_on_disk[0]);
    for (size_t i = 1; i < all_block_numbers_on_disk.size(); ++i)
    {
        if (all_block_numbers_on_disk[i].first == all_block_numbers_on_disk[i - 1].second + 1)
            block_numbers_on_disk.back().second = all_block_numbers_on_disk[i].second;
        else
            block_numbers_on_disk.push_back(all_block_numbers_on_disk[i]);