你只是错过了一个分组依据:)
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
Edit:
玩了一段时间后,我想我得到了您正在寻找的第一个解决方案。试一试 :)
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
对于下表:
+------------+----------+---------+
| 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 |
+------------+----------+---------+
数据变成这样:
+------------+------+------+-------+
| PARTNUMBER | SUP1 | SUP2 | SUP3 |
+------------+------+------+-------+
| a1 | | | Three |
| a2 | | Two | |
| a3 | | Two | Three |
| a4 | One | | |
| a5 | One | | Three |
| a6 | One | Two | |
| a7 | One | Two | Three |
+------------+------+------+-------+
最后进入这个:
+------------+-------+-------+-------+
| PARTNUMBER | SUPP1 | SUPP2 | SUPP3 |
+------------+-------+-------+-------+
| a1 | Three | | |
| a2 | Two | | |
| a3 | Two | Three | |
| a4 | One | | |
| a5 | One | Three | |
| a6 | One | Two | |
| a7 | One | Two | Three |
+------------+-------+-------+-------+