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)).
```

visited_nodes.insert(node);
            visited_index_names.insert(node->result_name);
            stack.push(const_cast<Node *>(node));
        }
    }
    if (add_missing_keys)
    {
        for (const auto & column : required_columns)
        {
            if (visited_index_names.find(column) == visited_index_names.end())
            {
                if (const ColumnWithTypeAndName * column_with_type_name = projection_block_for_keys.findByName(column))
                {
                    const auto * node = &addInput(*column_with_type_name);
                    visited_nodes.insert(node);
                    index.push_back(node);
                    visited_index_names.insert(column);
                }
                else
                {
                    
                    return {};
                }
            }
        }
    }
    while (!stack.empty())
    {
        auto * node = stack.top();
        stack.pop();