**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 (const auto & command : commands)
    {
        if (command.type == PartitionCommand::DROP_DETACHED_PARTITION
            && !settings.allow_drop_detached)
            throw DB::Exception("Cannot execute query: DROP DETACHED PART is disabled "
                                "(see allow_drop_detached setting)", ErrorCodes::SUPPORT_IS_DISABLED);
        if (command.partition && command.type != PartitionCommand::DROP_DETACHED_PARTITION)
        {
            if (command.part)
            {
                auto part_name = command.partition->as<ASTLiteral &>().value.safeGet<String>();
                
                MergeTreePartInfo::fromPartName(part_name, format_version);
            }
            else
            {
                
                getPartitionIDFromQuery(command.partition, global_context);
            }
        }
    }
}
void MergeTreeData::checkPartitionCanBeDropped(const ASTPtr & partition)