**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

MergeTreeData::getDetachedParts() const
{
    std::vector<DetachedPartInfo> res;
    for (const auto & [path, disk] : getRelativeDataPathsWithDisks())
    {
        for (auto it = disk->iterateDirectory(path + MergeTreeData::DETACHED_DIR_NAME); it->isValid(); it->next())
        {
            res.emplace_back();
            auto & part = res.back();
            DetachedPartInfo::tryParseDetachedPartName(it->name(), part, format_version);
            part.disk = disk->getName();
        }
    }
    return res;
}
void MergeTreeData::validateDetachedPartName(const String & name) const
{
    if (name.find('/') != std::string::npos || name == "." || name == "..")
        throw DB::Exception("Invalid part name '" + name + "'", ErrorCodes::INCORRECT_FILE_NAME);
    auto full_path = getFullRelativePathForPart(name, "detached/");
    if (!full_path)
        throw DB::Exception("Detached part \"" + name + "\" not found" , ErrorCodes::BAD_DATA_PART_NAME);
    if (startsWith(name, "attaching_") || startsWith(name, "deleting_"))
        throw DB::Exception("Cannot drop part " + name + ": "
                            "most likely it is used by another DROP or ATTACH query.",
                            ErrorCodes::BAD_DATA_PART_NAME);
}
void MergeTreeData::dropDetached(const ASTPtr & partition, bool part, const Context & context)