Method transform

src/Processors/Transforms/AddingDefaultsTransform.cpp:163–247

void AddingDefaultsTransform::transform(Chunk & chunk)
{
    if (column_defaults.empty())
        return;

    const BlockMissingValues & block_missing_values = input_format.getMissingValues();
    if (block_missing_values.empty())
        return;

    const auto & header = getOutputPort().getHeader();
    size_t num_rows = chunk.getNumRows();
    auto res = header.cloneWithColumns(chunk.detachColumns());

    /// res block already has all columns values, with default value for type
    /// (not value specified in table). We identify which columns we need to
    /// recalculate with help of block_missing_values.
    Block evaluate_block{res};
    /// remove columns for recalculation
    for (const auto & column : column_defaults)
    {
        if (evaluate_block.has(column.first))
        {
            size_t column_idx = res.getPositionByName(column.first);
            if (block_missing_values.hasDefaultBits(column_idx))
                evaluate_block.erase(column.first);
        }
    }

    if (!evaluate_block.columns())
        evaluate_block.insert({ColumnConst::create(ColumnUInt8::create(1, 0), num_rows), std::make_shared<DataTypeUInt8>(), "_dummy"});

    auto dag = evaluateMissingDefaults(evaluate_block, header.getNamesAndTypesList(), columns, context, false);
    if (dag)
    {
        auto actions = std::make_shared<ExpressionActions>(std::move(dag), ExpressionActionsSettings::fromContext(context, CompileExpressions::yes));
        actions->execute(evaluate_block);
    }

    std::unordered_map<size_t, MutableColumnPtr> mixed_columns;

    for (const ColumnWithTypeAndName & column_def : evaluate_block)
    {
        const String & column_name = column_def.name;

        if (column_defaults.count(column_name) == 0)
            continue;

        size_t block_column_position = res.getPositionByName(column_name);
        ColumnWithTypeAndName & column_read = res.getByPosition(block_column_position);
        const auto & defaults_mask = block_missing_values.getDefaultsBitmask(block_column_position);

        checkCalculated(column_read, column_def, defaults_mask.size());

        if (!defaults_mask.empty())
        {
            /// TODO: FixedString
            if (isColumnedAsNumber(column_read.type) || isDecimal(column_read.type))
            {