**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 Names & column_names,
    const DataTypes & data_types,
    const DiskPtr & disk_,
    const String & part_path,
    Checksums & out_checksums) const
{
    if (!initialized)
        throw Exception("Attempt to store uninitialized MinMax index for part " + part_path + ". This is a bug.",
            ErrorCodes::LOGICAL_ERROR);
    for (size_t i = 0; i < column_names.size(); ++i)
    {
        String file_name = "minmax_" + escapeForFileName(column_names[i]) + ".idx";
        const DataTypePtr & data_type = data_types.at(i);
        auto out = disk_->writeFile(part_path + file_name);
        HashingWriteBuffer out_hashing(*out);
        data_type->serializeBinary(hyperrectangle[i].left, out_hashing);
        data_type->serializeBinary(hyperrectangle[i].right, out_hashing);
        out_hashing.next();
        out_checksums.files[file_name].file_size = out_hashing.count();
        out_checksums.files[file_name].file_hash = out_hashing.getHash();
        out->finalize();
    }
}
void IMergeTreeDataPart::MinMaxIndex::update(const Block & block, const Names & column_names)