Change the table comment after created the table is not supported now?
Like mysql : ALTER TABLE [tableName] COMMNET [comment]; 
The sql "ALTER TABLE `system`.tables UPDATE Comment='test' WHERE NAME='t1';" also not supported!!!
My version is '21.9.4.35'。
Float64 num_streams_multiplier
        = std::min(unsigned(tables_count), std::max(1U, unsigned(local_context->getSettingsRef().max_streams_multiplier_for_merge_tables)));
    num_streams *= num_streams_multiplier;
    size_t remaining_streams = num_streams;
    InputOrderInfoPtr input_sorting_info;
    if (query_info.order_optimizer)
    {
        for (auto it = selected_tables.begin(); it != selected_tables.end(); ++it)
        {
            auto storage_ptr = std::get<1>(*it);
            auto storage_metadata_snapshot = storage_ptr->getInMemoryMetadataPtr();
            auto current_info = query_info.order_optimizer->getInputOrder(storage_metadata_snapshot, local_context);
            if (it == selected_tables.begin())
                input_sorting_info = current_info;
            else if (!current_info || (input_sorting_info && *current_info != *input_sorting_info))
                input_sorting_info.reset();
            if (!input_sorting_info)
                break;
        }
        query_info.input_order_info = input_sorting_info;
    }
    auto sample_block = getInMemoryMetadataPtr()->getSampleBlock();
    Names required_columns;
    for (const auto & table : selected_tables)
    {
        size_t current_need_streams = tables_count >= num_streams ? 1 : (num_streams / tables_count);
        size_t current_streams = std::min(current_need_streams, remaining_streams);
        remaining_streams -= current_streams;
        current_streams = std::max(size_t(1), current_streams);
        const auto & storage = std::get<1>(table);