**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

{
    switch (state)
    {
        case IMergeTreeDataPart::State::Temporary:
            CurrentMetrics::sub(CurrentMetrics::PartsTemporary);
            return;
        case IMergeTreeDataPart::State::PreCommitted:
            CurrentMetrics::sub(CurrentMetrics::PartsPreCommitted);
            return;
        case IMergeTreeDataPart::State::Committed:
            CurrentMetrics::sub(CurrentMetrics::PartsCommitted);
            return;
        case IMergeTreeDataPart::State::Outdated:
            CurrentMetrics::sub(CurrentMetrics::PartsOutdated);
            return;
        case IMergeTreeDataPart::State::Deleting:
            CurrentMetrics::sub(CurrentMetrics::PartsDeleting);
            return;
        case IMergeTreeDataPart::State::DeleteOnDestroy:
            CurrentMetrics::sub(CurrentMetrics::PartsDeleteOnDestroy);
            return;
    }
}
static void incrementTypeMetric(MergeTreeDataPartType type)