Function tryGetSubcolumnFromBlock

src/Interpreters/getColumnFromBlock.cpp:42–70

}

ColumnPtr tryGetSubcolumnFromBlock(const Block & block, const DataTypePtr & requested_column_type, const NameAndTypePair & requested_subcolumn)
{
    const auto * elem = block.findByName(requested_subcolumn.getNameInStorage());
    if (!elem)
        return nullptr;

    auto subcolumn_name = requested_subcolumn.getSubcolumnName();
    /// If requested subcolumn is dynamic, we should first perform cast and then
    /// extract the subcolumn, because the data of dynamic subcolumn can change after cast.
    if ((elem->type->hasDynamicStructure() || requested_column_type->hasDynamicStructure()) && !elem->type->equals(*requested_column_type))
    {
        auto cast_column = castColumn({elem->column->decompress(), elem->type, ""}, requested_column_type);
        auto elem_column = requested_column_type->tryGetSubcolumn(subcolumn_name, cast_column);
        auto elem_type = requested_column_type->tryGetSubcolumnType(subcolumn_name);

        if (!elem_type || !elem_column)
            return nullptr;

        return elem_column;
    }

    auto elem_column = elem->type->tryGetSubcolumn(subcolumn_name, elem->column->decompress());
    auto elem_type = elem->type->tryGetSubcolumnType(subcolumn_name);

    if (!elem_type || !elem_column)
        return nullptr;

    return castColumn({elem_column, elem_type, ""}, requested_subcolumn.type);
}

ColumnPtr getColumnFromBlock(const Block & block, const NameAndTypePair & requested_column)
{