**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

encountered_date_column = true;
            }
            else
            {
                
                minmax_idx_date_column_pos = -1;
            }
        }
    }
    if (!encountered_date_column)
    {
        for (size_t i = 0; i < minmax_idx_columns_types.size(); ++i)
        {
            if (typeid_cast<const DataTypeDateTime *>(minmax_idx_columns_types[i].get()))
            {
                if (!encountered_date_column)
                {
                    minmax_idx_time_column_pos = i;
                    encountered_date_column = true;
                }
                else
                {
                    
                    minmax_idx_time_column_pos = -1;
                }
            }
        }
    }
}
void MergeTreeData::checkTTLExpressions(const StorageInMemoryMetadata & new_metadata, const StorageInMemoryMetadata & old_metadata) const