**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

dropped_columns.emplace(command.column_name);
        }
        else if (command.isRequireMutationStage(getInMemoryMetadata()))
        {
            
            
            if (columns_alter_type_forbidden.count(command.column_name))
                throw Exception("ALTER of key column " + backQuoteIfNeed(command.column_name) + " is forbidden",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
            if (command.type == AlterCommand::MODIFY_COLUMN)
            {
                if (columns_alter_type_check_safe_for_partition.count(command.column_name))
                {
                    auto it = old_types.find(command.column_name);
                    assert(it != old_types.end());
                    if (!isSafeForKeyConversion(it->second, command.data_type.get()))
                        throw Exception("ALTER of partition key column " + backQuoteIfNeed(command.column_name) + " from type "
                                + it->second->getName() + " to type " + command.data_type->getName()
                                + " is not safe because it can change the representation of partition key",
                            ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);
                }
                if (columns_alter_type_metadata_only.count(command.column_name))
                {
                    auto it = old_types.find(command.column_name);
                    assert(it != old_types.end());
                    if (!isSafeForKeyConversion(it->second, command.data_type.get()))
                        throw Exception("ALTER of key column " + backQuoteIfNeed(command.column_name) + " from type "
                                    + it->second->getName() + " to type " + command.data_type->getName()
                                    + " is not safe because it can change the representation of primary key",
                            ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);