将 MERGE INTO 与 Scope_IDENTITY 结合使用

Question

当 Merge into 使用以下语句执行 insert 时，Scope_Identity 返回正确的代理键信息。但是，当执行更新时，Scope_Identity 和@@Identity 都会返回下一个可用代理键。当我添加 output 时，我在 update 和 insert 上都得到了 null。

如何在更新和插入上返回代理键？

DECLARE @Surrogate_KEY bigint


MERGE INTO [dbo].[MyTable] ChangeSet
USING (SELECT   @NaturalKey1 AS NaturalKey1, 
                @NaturalKey2 AS NaturalKey2, 
                @NaturalKey3 AS NaturalKey3,
                @Surrogate_KEY AS Surrogate_KEY) CurrentSet
ON  ChangeSet.NaturalKey1 = CurrentSet.NaturalKey1 AND 
    ChangeSet.NaturalKey2 = CurrentSet.NaturalKey2 AND 
    ChangeSet.NaturalKey3 = CurrentSet.NaturalKey3      
WHEN MATCHED THEN 
    UPDATE SET blah, blah, blah 

WHEN NOT MATCHED 
    THEN INSERT VALUES
       (
        blah, blah, blah
       )

output CurrentSet.*, @Surrogate_KEY ;

 print @Surrogate_KEY
 print @@IDENTITY
 print SCOPE_IDENTITY() 

Answer 1

在 OUTPUT 子句中使用插入伪表：

DECLARE @Surrogate_KEY bigint


MERGE INTO [dbo].[MyTable] ChangeSet
USING (SELECT   @NaturalKey1 AS NaturalKey1, 
                @NaturalKey2 AS NaturalKey2, 
                @NaturalKey3 AS NaturalKey3,
                @Surrogate_KEY AS Surrogate_KEY) CurrentSet
ON  ChangeSet.NaturalKey1 = CurrentSet.NaturalKey1 AND 
    ChangeSet.NaturalKey2 = CurrentSet.NaturalKey2 AND 
    ChangeSet.NaturalKey3 = CurrentSet.NaturalKey3      
WHEN MATCHED THEN 
    UPDATE SET blah, blah, blah 

WHEN NOT MATCHED 
    THEN INSERT VALUES
       (
        blah, blah, blah
       )

output inserted.* ;

这会返回任何内容这些值位于语句末尾的表（针对受影响的行）中。

Answer 2

DECLARE @Id ...
--
MERGE
    dbo.Table AS Tgt
USING
    (
        SELECT
            <Keys>
    ) AS Src
    ON Src.<Keys> = Tgt.<Keys>
WHEN MATCHED THEN
    UPDATE SET
        <...>
        ,@Id = Tgt.Id
WHEN NOT MATCHED THEN
    INSERT
    (
        ...
    )
    VALUES
    (
        ...
    )
;--
RETURN/SET/PRINT ISNULL(@Id, SCOPE_IDENTITY())