**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 "IMergeTreeDataPart.h"
#include <optional>
#include <Core/Defines.h>
#include <IO/HashingWriteBuffer.h>
#include <IO/ReadBufferFromString.h>
#include <IO/ReadHelpers.h>
#include <IO/WriteHelpers.h>
#include <Storages/MergeTree/MergeTreeData.h>
#include <Storages/MergeTree/localBackup.h>
#include <Storages/MergeTree/checkDataPart.h>
#include <Storages/StorageReplicatedMergeTree.h>
#include <Common/StringUtils/StringUtils.h>
#include <Common/escapeForFileName.h>
#include <Common/ZooKeeper/ZooKeeper.h>
#include <Common/CurrentMetrics.h>
#include <common/JSON.h>
#include <common/logger_useful.h>
#include <Compression/getCompressionCodecForFile.h>
#include <Parsers/queryToString.h>
#include <DataTypes/NestedUtils.h>
namespace CurrentMetrics
{
    extern const Metric PartsTemporary;