**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

{
    String path = getFullRelativePath() + "ttl.txt";
    if (volume->getDisk()->exists(path))
    {
        auto in = openForReading(volume->getDisk(), path);
        assertString("ttl format version: ", *in);
        size_t format_version;
        readText(format_version, *in);
        assertChar('\n', *in);
        if (format_version == 1)
        {
            try
            {
                ttl_infos.read(*in);
            }
            catch (const JSONException &)
            {
                throw Exception("Error while parsing file ttl.txt in part: " + name, ErrorCodes::BAD_TTL_FILE);
            }
        }
        else
            throw Exception("Unknown ttl format version: " + toString(format_version), ErrorCodes::BAD_TTL_FILE);
    }
}
void IMergeTreeDataPart::loadUUID()