**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 auto & storage_columns = metadata_snapshot->getColumns().getAllPhysical();
    auto alter_conversions = storage.getAlterConversionsForPart(shared_from_this());
    std::optional<std::string> minimum_size_column;
    UInt64 minimum_size = std::numeric_limits<UInt64>::max();
    for (const auto & column : storage_columns)
    {
        auto column_name = column.name;
        auto column_type = column.type;
        if (alter_conversions.isColumnRenamed(column.name))
            column_name = alter_conversions.getColumnOldName(column.name);
        if (!hasColumnFiles(column))
            continue;
        const auto size = getColumnSize(column_name, *column_type).data_compressed;
        if (size < minimum_size)
        {
            minimum_size = size;
            minimum_size_column = column_name;
        }
    }
    if (!minimum_size_column)
        throw Exception("Could not find a column of minimum size in MergeTree, part " + getFullPath(), ErrorCodes::LOGICAL_ERROR);
    return *minimum_size_column;
}
String IMergeTreeDataPart::getFullPath() const