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'。
DataStreams input_streams;
    input_streams.emplace_back(query_plan.getCurrentDataStream());
    input_streams.emplace_back(buffers_plan.getCurrentDataStream());
    std::vector<std::unique_ptr<QueryPlan>> plans;
    plans.emplace_back(std::make_unique<QueryPlan>(std::move(query_plan)));
    plans.emplace_back(std::make_unique<QueryPlan>(std::move(buffers_plan)));
    query_plan = QueryPlan();
    auto union_step = std::make_unique<UnionStep>(std::move(input_streams));
    union_step->setStepDescription("Unite sources from Buffer table");
    query_plan.unitePlans(std::move(union_step), std::move(plans));
}
static void appendBlock(const Block & from, Block & to)
{
    if (!to)
        throw Exception("Cannot append to empty block", ErrorCodes::LOGICAL_ERROR);
    if (to.rows())
        assertBlocksHaveEqualStructure(from, to, "Buffer");
    from.checkNumberOfRows();
    to.checkNumberOfRows();
    size_t rows = from.rows();
    size_t bytes = from.bytes();
    CurrentMetrics::add(CurrentMetrics::StorageBufferRows, rows);
    CurrentMetrics::add(CurrentMetrics::StorageBufferBytes, bytes);
    size_t old_rows = to.rows();
    MutableColumnPtr last_col;
    try
    {
        MemoryTracker::BlockerInThread temporarily_disable_memory_tracker;
        if (to.rows() == 0)
        {