**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

{
    DataPartPtr part_to_delete;
    {
        auto lock = lockParts();
        LOG_TRACE(log, "Trying to immediately remove part {}", part->getNameWithState());
        auto it = data_parts_by_info.find(part->info);
        if (it == data_parts_by_info.end() || (*it).get() != part.get())
            throw Exception("Part " + part->name + " doesn't exist", ErrorCodes::LOGICAL_ERROR);
        part.reset();
        if (!((*it)->getState() == DataPartState::Outdated && it->unique()))
            return;
        modifyPartState(it, DataPartState::Deleting);
        part_to_delete = *it;
    }
    try
    {
        part_to_delete->remove();
    }
    catch (...)
    {
        rollbackDeletingParts({part_to_delete});
        throw;
    }
    removePartsFinally({part_to_delete});
    LOG_TRACE(log, "Removed part {}", part_to_delete->name);
}
size_t MergeTreeData::getTotalActiveSizeInBytes() const