MySQL, множество редове за отделни полета

Просто ви липсва група от :)

SELECT PartNumber,
  MAX(IF (Priority = 0, SupName, NULL)) AS Sup1,
  MAX(IF (Priority = 1, SupName, NULL)) AS Sup2,
  MAX(IF (Priority = 2, SupName, NULL)) AS Sup3
FROM SupXref
GROUP BY PartNumber

Редактиране:

След като играх известно време, мисля, че получих първото решение, което търсите. Опитайте :)

SELECT partnumber,
  COALESCE(Sup1, COALESCE(Sup2, Sup3)) AS Supp1,
  IF (Sup1 IS NULL, IF (Sup2 IS NULL, NULL, Sup3), COALESCE(Sup2, Sup3)) AS Supp2,
  IF (Sup1 IS NULL, NULL, IF (Sup2 IS NULL, NULL, Sup3)) AS Supp3
FROM (
  SELECT PartNumber,
    MAX(IF (Priority = 0, SupName, NULL)) AS Sup1,
    MAX(IF (Priority = 1, SupName, NULL)) AS Sup2,
    MAX(IF (Priority = 2, SupName, NULL)) AS Sup3
  FROM SupXref
  GROUP BY PartNumber
) AS S

За следната таблица:

+------------+----------+---------+
| PARTNUMBER | PRIORITY | SUPNAME |
+------------+----------+---------+
| a1         |        2 | Three   |
| a2         |        1 | Two     |
| a3         |        2 | Three   |
| a3         |        1 | Two     |
| a4         |        0 | One     |
| a5         |        0 | One     |
| a5         |        2 | Three   |
| a6         |        0 | One     |
| a6         |        1 | Two     |
| a7         |        0 | One     |
| a7         |        1 | Two     |
| a7         |        2 | Three   |
+------------+----------+---------+

Данните се превръщат в това:

+------------+------+------+-------+
| PARTNUMBER | SUP1 | SUP2 | SUP3  |
+------------+------+------+-------+
| a1         |      |      | Three |
| a2         |      | Two  |       |
| a3         |      | Two  | Three |
| a4         | One  |      |       |
| a5         | One  |      | Three |
| a6         | One  | Two  |       |
| a7         | One  | Two  | Three |
+------------+------+------+-------+

И накрая в това:

+------------+-------+-------+-------+
| PARTNUMBER | SUPP1 | SUPP2 | SUPP3 |
+------------+-------+-------+-------+
| a1         | Three |       |       |
| a2         | Two   |       |       |
| a3         | Two   | Three |       |
| a4         | One   |       |       |
| a5         | One   | Three |       |
| a6         | One   | Two   |       |
| a7         | One   | Two   | Three |
+------------+-------+-------+-------+