22.2.1.4422.

```
create table test_alias (K Int64, D Date, S String, B Int64 Alias length(S)) Engine=MergeTree order by K;
insert into test_alias select number, today(), 'sdfsdfsdfsdfsdfds' from numbers(10000000);

session1: 
clickhouse-benchmark -c 10 <<< "insert into test_alias select number, today(), 'sdfsdfsdfsdfsdfds' from numbers(10000)"

session2: 
alter table test_alias drop column B;
0 rows in set. Elapsed: 251.043 sec.
```

especially it can be a problem with S3 disks

Alias columns do not persist in parts even in columns.txt
{
    if (from->equals(*to))
        return true;
    if (const auto * from_enum8 = typeid_cast<const DataTypeEnum8 *>(from))
    {
        if (const auto * to_enum8 = typeid_cast<const DataTypeEnum8 *>(to))
            return to_enum8->contains(*from_enum8);
    }
    if (const auto * from_enum16 = typeid_cast<const DataTypeEnum16 *>(from))
    {
        if (const auto * to_enum16 = typeid_cast<const DataTypeEnum16 *>(to))
            return to_enum16->contains(*from_enum16);
    }
    static const std::unordered_multimap<std::type_index, const std::type_info &> ALLOWED_CONVERSIONS =
        {
            { typeid(DataTypeEnum8),    typeid(DataTypeInt8)     },
            { typeid(DataTypeEnum16),   typeid(DataTypeInt16)    },
            { typeid(DataTypeDateTime), typeid(DataTypeUInt32)   },
            { typeid(DataTypeUInt32),   typeid(DataTypeDateTime) },
            { typeid(DataTypeDate),     typeid(DataTypeUInt16)   },
            { typeid(DataTypeUInt16),   typeid(DataTypeDate)     },
        };
    while (true)