**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

{
    LOG_TRACE(log, "dropAllData: waiting for locks.");
    auto lock = lockParts();
    LOG_TRACE(log, "dropAllData: removing data from memory.");
    DataPartsVector all_parts(data_parts_by_info.begin(), data_parts_by_info.end());
    data_parts_indexes.clear();
    column_sizes.clear();
    
    
    if (!getStorageID().hasUUID())
        global_context.dropCaches();
    LOG_TRACE(log, "dropAllData: removing data from filesystem.");
    
    clearPartsFromFilesystem(all_parts);
    for (const auto & [path, disk] : getRelativeDataPathsWithDisks())
    {
        try
        {
            disk->removeRecursive(path);
        }
        catch (const Poco::FileNotFoundException &)
        {
            
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
    }
    setDataVolume(0, 0, 0);
    LOG_TRACE(log, "dropAllData: done.");
}
void MergeTreeData::dropIfEmpty()