**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

part->volume->getDisk()->removeFileIfExists(backup_part_path + "/" + IMergeTreeDataPart::DELETE_ON_DESTROY_MARKER_FILE_NAME);
        part->is_frozen.store(true, std::memory_order_relaxed);
        result.push_back(PartitionCommandResultInfo{
            .partition_id = part->info.partition_id,
            .part_name = part->name,
            .backup_path = part->volume->getDisk()->getPath() + backup_path,
            .part_backup_path = part->volume->getDisk()->getPath() + backup_part_path,
            .backup_name = backup_name,
        });
        ++parts_processed;
    }
    LOG_DEBUG(log, "Freezed {} parts", parts_processed);
    return result;
}
PartitionCommandsResultInfo MergeTreeData::unfreezePartition(
    const ASTPtr & partition,
    const String & backup_name,
    const Context & context,
    TableLockHolder &)
{
    return unfreezePartitionsByMatcher(getPartitionMatcher(partition, context), backup_name, context);
}
PartitionCommandsResultInfo MergeTreeData::unfreezeAll(
    const String & backup_name,
    const Context & context,
    TableLockHolder &)
{
    return unfreezePartitionsByMatcher([] (const String &) { return true; }, backup_name, context);
}
PartitionCommandsResultInfo MergeTreeData::unfreezePartitionsByMatcher(MatcherFn matcher, const String & backup_name, const Context &)