Question

我有一个带有ID和D_DESC列的映射表。我想传递一个D_DESC值，传递多个ID，例如：

ID  D_DESC
1   DESC_ID1
2   DESC_ID2
3   DESC_ID3

结果应为

D_DESC1    D_DESC2
DESC_ID1   DESC_ID2

我做了这个查询：

SELECT t1.D_DESC AS DESC_1,t2.D_DESC AS DESC_2 
FROM  Tabel t1,Tabel t2 
WHERE '1'=t1.ID  
AND   '2'=t2.ID

返回正是我想要的，但如果我想在id未通过的情况下也将null值放入。例如，我还想从查询中显示此结果（ SELECT t1.D_DESC AS DESC_1,t2.D_DESC AS DESC_2 FROM Tabel t1,Tabel t2 WHERE '1'=t1.ID AND ''=t2.ID;）：

D_DESC1    D_DESC2
DESC_ID1   null

推荐？

Answer 1

如果您希望只有一行具有不同的IDS，那么您可以这样做：

select max(case when id = 1 then D_DESC end) DESC_1,
       max(case when id = 2 then D_DESC end) DESC_2
from table t;

Answer 2

这是PIVOT操作。

SELECT *
FROM Table1
PIVOT(MAX(D_DESC) FOR id IN (
             1 AS D_DESC1
            ,2 AS D_DESC2
            ,3 AS D_DESC3
            ));

这给出了：

|  D_DESC1 |  D_DESC2 |  D_DESC3 |
|----------|----------|----------|
| DESC_ID1 | DESC_ID2 | DESC_ID3 |

如果您想为NULL传递id2，请写

SELECT *
FROM Table1
PIVOT(MAX(D_DESC) FOR id IN (
            1 AS  D_DESC1
        ,NULL AS  D_DESC2
           ,3 AS  D_DESC3
            ));

给出了

|  D_DESC1 | D_DESC2 |  D_DESC3 |
|----------|---------|----------|
| DESC_ID1 |  (null) | DESC_ID3 |

从同一个表中获取来自不同ID的一列的值

2 个答案: