**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 StorageMetadataPtr & metadata_snapshot,
    UInt64 expected_size,
    const IMergeTreeDataPart::TTLInfos & ttl_infos,
    time_t time_of_move,
    size_t min_volume_index,
    bool is_insert,
    DiskPtr selected_disk) const
{
    expected_size = std::max(RESERVATION_MIN_ESTIMATION_SIZE, expected_size);
    ReservationPtr reservation = tryReserveSpacePreferringTTLRules(
        metadata_snapshot, expected_size, ttl_infos, time_of_move, min_volume_index, is_insert, selected_disk);
    return checkAndReturnReservation(expected_size, std::move(reservation));
}
ReservationPtr MergeTreeData::tryReserveSpacePreferringTTLRules(
    const StorageMetadataPtr & metadata_snapshot,
    UInt64 expected_size,
    const IMergeTreeDataPart::TTLInfos & ttl_infos,
    time_t time_of_move,
    size_t min_volume_index,
    bool is_insert,
    DiskPtr selected_disk) const
{
    expected_size = std::max(RESERVATION_MIN_ESTIMATION_SIZE, expected_size);
    ReservationPtr reservation;
    auto move_ttl_entry = selectTTLDescriptionForTTLInfos(metadata_snapshot->getMoveTTLs(), ttl_infos.moves_ttl, time_of_move, true);
    if (move_ttl_entry)
    {
        SpacePtr destination_ptr = getDestinationForMoveTTL(*move_ttl_entry, is_insert);
        if (!destination_ptr)