**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

extern const Metric PartsPreCommitted;
    extern const Metric PartsCommitted;
    extern const Metric PartsOutdated;
    extern const Metric PartsDeleting;
    extern const Metric PartsDeleteOnDestroy;
    extern const Metric PartsWide;
    extern const Metric PartsCompact;
    extern const Metric PartsInMemory;
}
namespace DB
{
namespace ErrorCodes
{
    extern const int DIRECTORY_ALREADY_EXISTS;
    extern const int CANNOT_READ_ALL_DATA;
    extern const int LOGICAL_ERROR;
    extern const int FILE_DOESNT_EXIST;
    extern const int NO_FILE_IN_DATA_PART;
    extern const int EXPECTED_END_OF_FILE;
    extern const int CORRUPTED_DATA;
    extern const int NOT_FOUND_EXPECTED_DATA_PART;
    extern const int BAD_SIZE_OF_FILE_IN_DATA_PART;
    extern const int BAD_TTL_FILE;
    extern const int NOT_IMPLEMENTED;
}
static std::unique_ptr<ReadBufferFromFileBase> openForReading(const DiskPtr & disk, const String & path)
{
    return disk->readFile(path, std::min(size_t(DBMS_DEFAULT_BUFFER_SIZE), disk->getFileSize(path)));
}
void IMergeTreeDataPart::MinMaxIndex::load(const MergeTreeData & data, const DiskPtr & disk_, const String & part_path)