
```
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 (visited_nodes.count(child) == 0)
            {
                visited_nodes.insert(child);
                stack.push({.node = child, .is_predicate = is_conjunction});
                break;
            }
            if (allowed_nodes.contains(child))
                ++cur.num_allowed_children;
            ++cur.next_child_to_visit;
        }
        if (cur.next_child_to_visit == cur.node->children.size())
        {
            if (cur.num_allowed_children == cur.node->children.size())
            {
                if (cur.node->type != ActionsDAG::ActionType::ARRAY_JOIN && cur.node->type != ActionsDAG::ActionType::INPUT)
                    allowed_nodes.emplace(cur.node);
            }
            else if (is_conjunction)
            {
                for (const auto * child : cur.node->children)
                {
                    if (allowed_nodes.count(child))
                    {
                        if (allowed.insert(child).second)
                            conjunction.allowed.push_back(child);
                    }
                }
            }
            else if (cur.is_predicate)
            {