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
{
    const DataTypeFactory & data_type_factory = DataTypeFactory::instance();
    if (command_ast->type == ASTAlterCommand::ADD_COLUMN)
    {
        AlterCommand command;
        command.ast = command_ast->clone();
        command.type = AlterCommand::ADD_COLUMN;
        const auto & ast_col_decl = command_ast->col_decl->as<ASTColumnDeclaration &>();
        command.column_name = ast_col_decl.name;
        if (ast_col_decl.type)
        {
            command.data_type = data_type_factory.get(ast_col_decl.type);
        }
        if (ast_col_decl.default_expression)
        {
            command.default_kind = columnDefaultKindFromString(ast_col_decl.default_specifier);
            command.default_expression = ast_col_decl.default_expression;
        }
        if (ast_col_decl.comment)
        {
            const auto & ast_comment = typeid_cast<ASTLiteral &>(*ast_col_decl.comment);
            command.comment = ast_comment.value.get<String>();
        }
        if (ast_col_decl.codec)
        {
            if (ast_col_decl.default_specifier == "ALIAS")
                throw Exception{"Cannot specify codec for column type ALIAS", ErrorCodes::BAD_ARGUMENTS};