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)).
```

{
    NodeRawConstPtrs required_nodes;
    required_nodes.reserve(required_names.size());
    NameSet added;
    for (const auto & node : index)
    {
        if (required_names.count(node->result_name) && added.count(node->result_name) == 0)
        {
            required_nodes.push_back(node);
            added.insert(node->result_name);
        }
    }
    if (added.size() < required_names.size())
    {
        for (const auto & name : required_names)
            if (added.count(name) == 0)
                throw Exception(ErrorCodes::UNKNOWN_IDENTIFIER,
                                "Unknown column: {}, there are only columns {}", name, dumpNames());
    }
    index.swap(required_nodes);
    removeUnusedActions();
}
void ActionsDAG::removeUnusedActions(const Names & required_names)