**Use case**
mysql repl to clickhouse

**Describe the solution you'd like**
Hope MaterializeMySQL engine can support MySQL prefix index



auto rewritten_command = std::make_shared<ASTAlterCommand>();
                rewritten_command->type = ASTAlterCommand::ADD_COLUMN;
                rewritten_command->first = alter_command->first;
                rewritten_command->col_decl = additional_columns->children[index]->clone();
                const auto & column_declare = alter_command->additional_columns->children[index]->as<MySQLParser::ASTDeclareColumn>();
                if (column_declare && column_declare->column_options)
                {
                    
                    const auto & column_options = column_declare->column_options->as<MySQLParser::ASTDeclareOptions>();
                    const auto & default_expression_it = column_options->changes.find("default");
                    if (default_expression_it != column_options->changes.end())
                    {
                        ASTColumnDeclaration * col_decl = rewritten_command->col_decl->as<ASTColumnDeclaration>();
                        col_decl->default_specifier = "DEFAULT";
                        col_decl->default_expression = default_expression_it->second->clone();
                        col_decl->children.emplace_back(col_decl->default_expression);
                    }
                }
                if (default_after_column.empty())
                {
                    StoragePtr storage = DatabaseCatalog::instance().getTable({mapped_to_database, alter_query.table}, context);
                    Block storage_header = storage->getInMemoryMetadataPtr()->getSampleBlock();
                    
                    default_after_column = storage_header.getByPosition(storage_header.columns() - 3).name;
                }
                if (!alter_command->column_name.empty())
                {
                    rewritten_command->column = std::make_shared<ASTIdentifier>(alter_command->column_name);
                    rewritten_command->children.push_back(rewritten_command->column);