There are three relations (t1, t2, t3):

```
t1
-----------
 a  | b

 1  | 2
----------- 

t2
------------
  b  |  c

  2  | 3
------------

t3
-------------
  a  |  c

  4  |  5
-------------

```

The query is:

```
select * from t1 natural full outer join (t2 natural full outer join t3); 

```

The result of `select * from t2 natural full outer join t3` is:

```
-----------------
  a  |  b  |  c

     | 2   | 3

  4  |     | 5
------------------

```

then I tried:

`select * from t1 natural full outer join (result)`

```
    t1             result
-----------      -----------------
 a  | b           a    |  b  | c

 1  | 2                | 2   | 3

                    4  |     | 5
                 ------------------

```

Shouldn't this be:

```
--------------------------
   a    |  b  |  c

   1    |  2  | 3

  4     |     | 5

```

But I don't know why the sql query give:

```
 a | b | c 

 4 |   | 5
   | 2 | 3
 1 | 2 | 

```