
```
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))
```
{
                    child_data.needed_by_split_node = true;
                    stack.push({.node = child});
                }
            }
        }
    }
    
    for (const auto & node : nodes)
    {
        if (!data[&node].visited)
            stack.push({.node = &node});
        while (!stack.empty())
        {
            auto & cur = stack.top();
            auto & cur_data = data[cur.node];
            
            while (cur.next_child_to_visit < cur.node->children.size())
            {
                const auto * child = cur.node->children[cur.next_child_to_visit];
                auto & child_data = data[child];
                if (!child_data.visited)
                {
                    stack.push({.node = child});
                    break;
                }
                ++cur.next_child_to_visit;
            }
            
            if (cur.next_child_to_visit == cur.node->children.size())