**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

const Context & context, PartsTemporaryRename & renamed_parts)
{
    String source_dir = "detached/";
    std::map<String, DiskPtr> name_to_disk;
    
    if (attach_part)
    {
        String part_id = partition->as<ASTLiteral &>().value.safeGet<String>();
        validateDetachedPartName(part_id);
        renamed_parts.addPart(part_id, "attaching_" + part_id);