product
---------------
| id |  name  |
---------------
| 1  |  Name  |
| 2  |  ....  |

       attribute
-------------------------
|p_id|a_id|m_id|  text  |
-------------------------
| 1  | 5  | 1  | aaaaaa |
| 1  | 8  | 1  | AAAAAA |
| 2  | 5  | 1  | bbbbbb |
| 2  | 8  | 1  | BBBBBB |
| 2  | 5  | 2  | ...... |
| 2  | 8  | 2  | ...... |


Требуемый результат:
-------------------------
| id |    a    |   b    |
-------------------------
| 1  |  aaaaaa | AAAAAA |
| 2  |  bbbbbb | BBBBBB |

SELECT p.id as id, productA.a as a, productB.b as b
FROM product as p
INNER JOIN 
(
    SELECT text as a, attribute.p_id as id
    FROM attribute, product
    WHERE attribute.p_id = product.id AND m_id = '1' AND a_id = '5'    
) as productA ON productA.id = p.id
INNER JOIN 
(
    SELECT text as b, attribute.p_id as id
    FROM attribute, product
    WHERE attribute.p_id = product.id AND m_id = '1' AND a_id = '8'    
) as productB ON productB.id = p.id
GROUP BY id