**How to reproduce**
Clickhouse server 20.13.1.5273
```
CREATE TABLE default.test
(
`key` UInt32,
`ts` DateTime CODEC(DoubleDelta, LZ4),
`db_time` DateTime DEFAULT now() COMMENT 'spout-ignore' CODEC(DoubleDelta, LZ4)
)
ENGINE = MergeTree
PARTITION BY toStartOfTenMinutes(db_time)
ORDER BY (key, ts)
TTL db_time + toIntervalHour(3)
SETTINGS index_granularity = 8192, merge_with_ttl_timeout = 3600, min_rows_for_compact_part = 1000000, min_bytes_for_compact_part = 200000000, in_memory_parts_enable_wal = 0;


INSERT INTO test(key, ts) SELECT number % 1000, now() + intDiv(number,1000) FROM numbers(500);

SELECT * FROM test;
500 rows in set. Elapsed: 0.003 sec.

DETACH TABLE test;

ATTACH TABLE test;

SELECT * FROM test;

0 rows in set. Elapsed: 0.002 sec.
```

**Expected behavior**
Clickhouse would flush parts on disk.
NameSet dropped_columns;
    std::map<String, const IDataType *> old_types;
    for (const auto & column : old_metadata.getColumns().getAllPhysical())
        old_types.emplace(column.name, column.type.get());
    NamesAndTypesList columns_to_check_conversion;
    auto name_deps = getDependentViewsByColumn(local_context);
    for (const AlterCommand & command : commands)
    {
        
        if (command.partition)
        {
            getPartitionIDFromQuery(command.partition, getContext());
        }
        if (command.column_name == merging_params.version_column)
        {
            
            if (command.type == AlterCommand::MODIFY_COLUMN)
            {
                const IDataType * new_type = command.data_type.get();
                const IDataType * old_type = old_types[command.column_name];
                if (new_type)
                    checkVersionColumnTypesConversion(old_type, new_type, command.column_name);
                
                continue;
            }
            else if (command.type == AlterCommand::DROP_COLUMN)
            {
                throw Exception(
                    "Trying to ALTER DROP version " + backQuoteIfNeed(command.column_name) + " column",
                    ErrorCodes::ALTER_OF_COLUMN_IS_FORBIDDEN);