
```
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))
```
}
    node.result_name = std::move(result_name);
    return addNode(std::move(node));
}
const ActionsDAG::Node & ActionsDAG::findInIndex(const std::string & name) const
{
    if (const auto * node = tryFindInIndex(name))
        return *node;
    throw Exception(ErrorCodes::UNKNOWN_IDENTIFIER, "Unknown identifier: '{}'", name);
}
const ActionsDAG::Node * ActionsDAG::tryFindInIndex(const std::string & name) const
{
    for (const auto & node : index)
        if (node->result_name == name)
            return node;
    return nullptr;
}
void ActionsDAG::addOrReplaceInIndex(const Node & node)
{
    for (auto & index_node : index)
    {
        if (index_node->result_name == node.result_name)
        {
            index_node = &node;
            return;
        }
    }
    index.push_back(&node);
}
NamesAndTypesList ActionsDAG::getRequiredColumns() const