**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

* Precommitted -> Committed:    we successfully committed a part to active dataset
     * Precommitted -> Outdated:    a part was replaced by a covering part or DROP PARTITION
     * Outdated -> Deleting:        a cleaner selected this part for deletion
     * Deleting -> Outdated:        if an ZooKeeper error occurred during the deletion, we will retry deletion
     * Committed -> DeleteOnDestroy if part was moved to another disk
     */
    enum class State
    {
        Temporary,       
        PreCommitted,    
        Committed,       
        Outdated,        
        Deleting,        
        DeleteOnDestroy, 
    };
    using TTLInfo = MergeTreeDataPartTTLInfo;
    using TTLInfos = MergeTreeDataPartTTLInfos;
    TTLInfos ttl_infos;
    
    void setState(State new_state) const;
    State getState() const;
    
    static String stateToString(State state);
    String stateString() const;
    String getNameWithState() const
    {
        return name + " (state " + stateString() + ")";
    }
    
    bool checkState(const std::initializer_list<State> & affordable_states) const