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
{
    auto columns = metadata.columns;
    for (size_t i = 0; i < size(); ++i)
    {
        auto & command = (*this)[i];
        bool has_column = columns.has(command.column_name) || columns.hasNested(command.column_name);
        if (command.type == AlterCommand::MODIFY_COLUMN)
        {
            if (!has_column && command.if_exists)
                command.ignore = true;
            if (has_column)
            {
                auto column_from_table = columns.get(command.column_name);
                if (command.data_type && !command.default_expression && column_from_table.default_desc.expression)
                {
                    command.default_kind = column_from_table.default_desc.kind;
                    command.default_expression = column_from_table.default_desc.expression;
                }
            }
        }
        else if (command.type == AlterCommand::ADD_COLUMN)
        {
            if (has_column && command.if_not_exists)
                command.ignore = true;
        }