Question

在连接具有一对多关系的两个表时，我想要一个结果，在一个表中显示多个表中具有null值的所有值。

以下是一个例子：

tbl_Platform：PriKey = PlatformID

PlatformID  PlatformDesc
1   Application
2   Cloud
3   Storage
4   Backup

tbl_Missed：PriKey = CustomerID + Week + PlatformID

CustomerID  Week    Missed     Platform ID
49          1       2017-05-19  1

所需输出：

CustomerID  Week    Missed  PlatformDesc
49  1   2017-05-19  Application
49  1   null    Cloud
49  1   null    Storage
49  1   null    Backup

我最接近的是使用交叉连接，如下所示：

SELECT        
   dbo.tbl_Missed.CustomerID, 
   dbo.tbl_Missed.Week, 
   dbo.tbl_Missed.Missed, 
   dbo.tbl_Platform.PlatformDesc
FROM
   dbo.tbl_Platform 
CROSS JOIN dbo.tbl_MissedSPT

这给了我：

49  1   2017-05-19  Application
49  1   2017-05-19  Cloud
49  1   2017-05-19  Storage
49  1   2017-05-19  Backup

Answer 1

如果missed中存在匹配，则好像您想要获取属性platformID的值，否则null。尝试以下（希望没有拼写错误）：

SELECT        
   dbo.tbl_Missed.CustomerID, 
   dbo.tbl_Missed.week, 
   CASE WHEN dbo.tbl_Missed.PlatformID = dbo.tbl_Platform.PlatformID
               THEN dbo.tbl_Missed.missed 
               ELSE NULL
   END as missed, 
   dbo.tbl_Platform.PlatformDesc
FROM dbo.tbl_Platform CROSS JOIN dbo.tbl_MissedSPT

SQL隐含连接表中的空值

1 个答案: