i dont remember how to join a table to itself.. my table is:

```
| id | proc | value | kind |
| 1  | 1    | foo   | a    |
| 2  | 1    | bar   | b    |
| 3  | 2    | some  | a    |

```

And i need to retrieve the value col where proc is $proc and kind is both 'a' and 'b'.. well, i need to do have that (looking for proc = 1):

```
| v_a | v_b |
| foo | bar |

```

So i wrote this query:

```
SELECT
    a.value AS v_a,
    b.value AS v_b
FROM
    (SELECT value FROM table WHERE proc = '1' AND kind = 'a') AS a,
    (SELECT value FROM table WHERE proc = '1' AND kind = 'b') AS b

```

And works but only if in the table i have both rows for kind=a and kind=b.

But i need that if miss a row, i'll have a null value: if i look for proc=2 i must get:

```
| v_a | v_b |
| foo | NULL|

```

Instead, with my query i dont get anythong if the b or a row is missing.

Im working with mysql...How to do that?

**Edit:**
I could use the UNION clause, but this wont allow me to have a NULL value when one row is missing (kind=a or kind=b)