如果 id 没有记录，SQL Server 合并语句返回零答案

【问题标题】：SQL Server Merge Statement to return zero if no record for an id如果 id 没有记录，SQL Server 合并语句返回零
【发布时间】：2019-05-16 11:24:57
【问题描述】：

我正在使用合并语句来更新 ModuleEnrollment 表中完成的课程数。这可行，但是如果从 Employee 中删除课程，则它仍保持其先前的值。有没有办法在合并语句中包含任何 EmployeeID 未包含在 CoursesComplete 表中的返回 0。

 MERGE [dbo].[ModuleEnrollment] as ME
 USING  [dbo].[CoursesComplete]AS CC
 ON ME.[EmployeeID] = CC.[EmployeeID] AND ME.[ModuleID] = CC.[ModuleID]
 WHEN MATCHED THEN
      UPDATE SET ME.[CoursesComplete]=CC.[CoursesComplete]
 WHEN NOT MATCHED BY TARGET THEN
      INSERT([EmployeeID],[ModuleID],[CoursesComplete]) VALUES(CC. 
[EmployeeID],CC.[ModuleID],CC.[CoursesComplete]);

GO

【问题讨论】：

标签： sql-server merge

【解决方案1】：

您只需添加：

WHEN NOT MATCHED BY SOURCE THEN 
    UPDATE SET ME.[CoursesComplete]=0

整个查询：

;MERGE [dbo].[ModuleEnrollment] as ME
 USING  [dbo].[CoursesComplete]AS CC
 ON ME.[EmployeeID] = CC.[EmployeeID] AND ME.[ModuleID] = CC.[ModuleID]
 WHEN MATCHED THEN
      UPDATE SET ME.[CoursesComplete]=CC.[CoursesComplete]
 WHEN NOT MATCHED BY TARGET THEN
      INSERT([EmployeeID],[ModuleID],[CoursesComplete]) VALUES(CC. 
[EmployeeID],CC.[ModuleID],CC.[CoursesComplete])
WHEN NOT MATCHED BY SOURCE THEN 
        UPDATE SET ME.[CoursesComplete]=0;

【讨论】：