**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

{
    UInt64 res = 0;
    for (const ColumnPtr & column : index)
        res += column->allocatedBytes();
    return res;
}
String IMergeTreeDataPart::stateToString(IMergeTreeDataPart::State state)
{
    switch (state)
    {
        case State::Temporary:
            return "Temporary";
        case State::PreCommitted:
            return "PreCommitted";
        case State::Committed:
            return "Committed";
        case State::Outdated:
            return "Outdated";
        case State::Deleting:
            return "Deleting";
        case State::DeleteOnDestroy:
            return "DeleteOnDestroy";
    }
    __builtin_unreachable();
}
String IMergeTreeDataPart::stateString() const
{
    return stateToString(state);
}
void IMergeTreeDataPart::assertState(const std::initializer_list<IMergeTreeDataPart::State> & affordable_states) const