SQL 数据透视字符串数据

Question

我在 SQL Server 中有一个表:Product

产品表:

ImageID  ProductID  
-------  ---------- 
1           P1
1           P2             
1           P3             
2           S1
2           S2
2           S3
3           M1

这是我需要的输出:

ImageID  Product1ID     Product2ID      Product3ID
----------- ---------- ----------    ----------
1           P1             P2           P3
2           S1             S2           S3
3           M1             null         null

一个ImageID最多可以有3个ProductID没有必要所有 ImageID 都有 3 个产品 [例如。图片ID=3]

SELECT ImageID, [Product1ID], [Product2ID], [Product3ID]
FROM    
(  
        SELECT ImageID,  ProductID
        FROM ProductTable
) AS P
PIVOT 
(  
    max( ImageID) 
    FOR ProductID IN ([Product1ID], [Product2ID], [Product3ID])
) AS  PVT

Answer 1

我只会使用条件聚合:

SELECT ImageID,
       MAX(CASE WHEN seqnum = 1 THEN ProductID END) as Product1ID,
       MAX(CASE WHEN seqnum = 2 THEN ProductID END) as Product2ID,
       MAX(CASE WHEN seqnum = 3 THEN ProductID END) as Product3ID
FROM (SELET pt.*, ROW_NUMBER() OVER (PARTITION BY ImageId ORDER BY ProductID) as seqnum
      FROM ProductTable
     ) P
GROUP BY ImageID;

不过，关键思想是使用 ROW_NUMBER() 来枚举产品。