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)).
```

}
    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