**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

#include <optional>
#include <set>
#include <thread>
#include <typeinfo>
#include <typeindex>
#include <unordered_set>
namespace ProfileEvents
{
    extern const Event RejectedInserts;
    extern const Event DelayedInserts;
    extern const Event DelayedInsertsMilliseconds;
}
namespace CurrentMetrics
{
    extern const Metric DelayedInserts;
    extern const Metric BackgroundMovePoolTask;
}
namespace
{
    constexpr UInt64 RESERVATION_MIN_ESTIMATION_SIZE = 1u * 1024u * 1024u; 
}
namespace DB
{
namespace ErrorCodes
{
    extern const int NO_SUCH_DATA_PART;
    extern const int NOT_IMPLEMENTED;
    extern const int DIRECTORY_ALREADY_EXISTS;
    extern const int TOO_MANY_UNEXPECTED_DATA_PARTS;
    extern const int DUPLICATE_DATA_PART;