:)
によるグループが欠落しているだけです。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
編集：
しばらく遊んだ後、私はあなたが探している最初の解決策を得たと思います。試してみてください:)
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
次の表の場合：
+------------+----------+---------+
| 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 |
+------------+----------+---------+
データは次のようになります：
+------------+------+------+-------+
| PARTNUMBER | SUP1 | SUP2 | SUP3 |
+------------+------+------+-------+
| a1 | | | Three |
| a2 | | Two | |
| a3 | | Two | Three |
| a4 | One | | |
| a5 | One | | Three |
| a6 | One | Two | |
| a7 | One | Two | Three |
+------------+------+------+-------+
そして最後にこれに：
+------------+-------+-------+-------+
| PARTNUMBER | SUPP1 | SUPP2 | SUPP3 |
+------------+-------+-------+-------+
| a1 | Three | | |
| a2 | Two | | |
| a3 | Two | Three | |
| a4 | One | | |
| a5 | One | Three | |
| a6 | One | Two | |
| a7 | One | Two | Three |
+------------+-------+-------+-------+