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)).
```

for (const auto * child : node->children)
        {
            if (visited_nodes.count(child) == 0)
            {
                stack.push(const_cast<Node *>(child));
                visited_nodes.insert(child);
            }
        }
    }
    nodes.remove_if([&](const Node & node) { return visited_nodes.count(&node) == 0; });
    auto it = std::remove_if(inputs.begin(), inputs.end(), [&](const Node * node) { return visited_nodes.count(node) == 0; });
    inputs.erase(it, inputs.end());
}
static ColumnWithTypeAndName executeActionForHeader(const ActionsDAG::Node * node, ColumnsWithTypeAndName arguments)
{
    ColumnWithTypeAndName res_column;
    res_column.type = node->result_type;
    res_column.name = node->result_name;
    switch (node->type)
    {
        case ActionsDAG::ActionType::FUNCTION:
        {
            
            
            
            
            res_column.column = node->function->execute(arguments, res_column.type, 0, true);
            
            
            break;