
```
select *
from (
select 'table' as table, toInt64(10) as rows, toInt64(101) as elements
union all
select 'another table' as table, toInt64(0) as rows, toInt64(0) as elements
)
where rows - elements <> 0

DB::Exception: Block structure mismatch in Pipe::unitePipes stream: different number of columns:
table String String(size = 0), rows Int64 Int64(size = 0), elements Int64 Int64(size = 0)
table String String(size = 0), rows Int64 Int64(size = 0), elements Int64 Int64(size = 0), dummy UInt8 UInt8(size = 0) (version 21.5.3.1 (official build))
```
}
                    
                    if (copy.type == ActionType::INPUT)
                    {
                        auto & input_copy = first_nodes.emplace_back(*cur.node);
                        assert(cur_data.to_first == nullptr);
                        cur_data.to_first = &input_copy;
                        new_inputs.push_back(cur.node);
                    }
                }
                else
                {
                    auto & copy = first_nodes.emplace_back(*cur.node);
                    cur_data.to_first = &copy;
                    
                    for (auto & child : copy.children)
                    {
                        child = data[child].to_first;
                        assert(child != nullptr);
                    }
                    if (cur_data.used_in_result)
                    {
                        
                        Node input_node;
                        input_node.type = ActionType::INPUT;
                        input_node.result_type = node.result_type;
                        input_node.result_name = node.result_name;
                        cur_data.to_second = &second_nodes.emplace_back(std::move(input_node));
                        new_inputs.push_back(cur.node);
                    }