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 (column_to_modify.default_desc.expression)
                    rename_visitor.visit(column_to_modify.default_desc.expression);
                if (column_to_modify.ttl)
                    rename_visitor.visit(column_to_modify.ttl);
            });
        }
        if (metadata.table_ttl.definition_ast)
            rename_visitor.visit(metadata.table_ttl.definition_ast);
        auto constraints_data = metadata.constraints.getConstraints();
        for (auto & constraint : constraints_data)
            rename_visitor.visit(constraint);
        metadata.constraints = ConstraintsDescription(constraints_data);
        if (metadata.isSortingKeyDefined())
            rename_visitor.visit(metadata.sorting_key.definition_ast);
        if (metadata.isPrimaryKeyDefined())
            rename_visitor.visit(metadata.primary_key.definition_ast);
        if (metadata.isSamplingKeyDefined())
            rename_visitor.visit(metadata.sampling_key.definition_ast);
        if (metadata.isPartitionKeyDefined())
            rename_visitor.visit(metadata.partition_key.definition_ast);
        for (auto & index : metadata.secondary_indices)
            rename_visitor.visit(index.definition_ast);
    }
    else
        throw Exception("Wrong parameter type in ALTER query", ErrorCodes::LOGICAL_ERROR);
}
namespace
{
bool isMetadataOnlyConversion(const IDataType * from, const IDataType * to)