You have to provide the following information whenever possible.

**Describe the bug**
This query fails with the latest stable version 21.5.5.12. It worked with the last stable version 21.4.7.3.

**Does it reproduce on recent release?**
yes

**How to reproduce**
21.5.5.12

```
SELECT
    label,
    number
FROM
(
    SELECT
        'a' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
    UNION ALL
    SELECT
        'b' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
)
WHERE number IN
(
    SELECT number
    FROM numbers(5)
)
```

**Expected behavior**
Query should run without errors

**Error message and/or stacktrace**
```
Received exception from server (version 21.5.5):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Block structure mismatch in Pipe::unitePipes stream: different names of columns:
label String String(size = 0), number UInt64 UInt64(size = 0), 'b' String Const(size = 0, String(size = 1))
label String String(size = 0), number UInt64 UInt64(size = 0), 'a' String Const(size = 0, String(size = 1)).
```

}
                    
                    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);
                    }