
```
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 (nodes_mapping.count(predicate))
            continue;
        stack.push({.node = predicate});
        while (!stack.empty())
        {
            auto & cur = stack.top();
            
            while (cur.next_child_to_visit < cur.node->children.size())
            {
                const auto * child = cur.node->children[cur.next_child_to_visit];
                if (nodes_mapping.count(child) == 0)
                {
                    stack.push({.node = child});
                    break;
                }
                ++cur.next_child_to_visit;
            }
            if (cur.next_child_to_visit == cur.node->children.size())
            {
                auto & node = actions->nodes.emplace_back(*cur.node);
                nodes_mapping[cur.node] = &node;
                for (auto & child : node.children)
                    child = nodes_mapping[child];
                if (node.type == ActionType::INPUT)
                    required_inputs[node.result_name].push_back(&node);
                stack.pop();
            }
        }
    }
    const Node * result_predicate = nodes_mapping[*conjunction.begin()];