**How to reproduce**
Clickhouse version 21.2-21.3

```
SELECT x
FROM
(
    SELECT 1 AS x
    UNION DISTINCT
    SELECT 1
)
LIMIT 1

Query id: b82bbb8d-dea9-4f1c-9a2f-5b0e9b6c2422


0 rows in set. Elapsed: 0.002 sec.

Received exception from server (version 21.2.3):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Bad cast from type DB::ASTSelectWithUnionQuery to DB::ASTSelectQuery.
```


{
            return true;
        }
        else if (left[i].column_number > right[i].column_number)
        {
            return false;
        }
        else if (left[i].direction < right[i].direction)
        {
            return true;
        }
        else if (left[i].direction > right[i].direction)
        {
            return false;
        }
        else if (left[i].nulls_direction < right[i].nulls_direction)
        {
            return true;
        }
        else if (left[i].nulls_direction > right[i].nulls_direction)
        {
            return false;
        }
        assert(left[i] == right[i]);
    }
    
    
    return left.size() > right.size();
}
static bool sortIsPrefix(const WindowDescription & _prefix,