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)).
```

ErrorCodes::THERE_IS_NO_COLUMN);
                }
                else
                {
                    src_node = dst_node = actions_dag->inputs[input.front()];
                    input.pop_front();
                }
                break;
            }
        }
        
        if (const auto * res_const = typeid_cast<const ColumnConst *>(res_elem.column.get()))
        {
            if (const auto * src_const = typeid_cast<const ColumnConst *>(dst_node->column.get()))
            {
                if (ignore_constant_values)
                    dst_node = &actions_dag->addColumn(res_elem);
                else if (res_const->getField() != src_const->getField())
                    throw Exception("Cannot convert column " + backQuote(res_elem.name) + " because "
                                    "it is constant but values of constants are different in source and result",
                                    ErrorCodes::ILLEGAL_COLUMN);
            }
            else
                throw Exception("Cannot convert column " + backQuote(res_elem.name) + " because "
                                "it is non constant in source stream but must be constant in result",
                                ErrorCodes::ILLEGAL_COLUMN);
        }
        
        if (!res_elem.type->equals(*dst_node->result_type))
        {