Sql server 合并中的更新行为不同？它没有'；插入时无法获取上下文信息（）

我创建了以下两个带有触发器的测试表来记录所有操作（插入、删除和更新）

设置表和触发器：

-- drop table test; drop table testLog
create table test (id int identity primary key, x int);
create table testLog (idx int identity primary key, Action varchar(10), id int not null, 
    x_deleted int, x_inserted int, uid uniqueidentifier);
go
-- Trigger to log the changes
create trigger trigger_test on test
    after insert, delete, update
as
declare @id uniqueidentifier = context_info();
print @id;

insert testLog (id, Action, x_deleted, x_inserted, uid)
select  isnull(d.id, i.id) ,
        case when i.id is not null and d.id is not null then 'Updated'
             when d.id is not null then 'Deleted'
             when i.id is not null then 'Inserted'
        end ,
        d.x ,
        i.x ,
        @id
from    Deleted d
        full outer join inserted i on i.id = d.id;

set context_info 0;
go 

现在插入一些示例数据

set context_info 0
insert test (x) values (10), (20), (30), (40), (50);
SELECT * FROM test;
SELECT * FROM testLog
go

下面的语句工作正常。正确的

context\u info（）

保存在日志表中

begin tran
declare @newid uniqueidentifier = newid()
-- 
set context_info @newid
print @newid
insert test(x) values (1)

set context_info @newid
update test set x = 2 where id = 1
SELECT * FROM dbo.testLog;
rollback
go

但是，只有插入部分的

合并

在

上下文信息（）中获得了值。

---

最近两次更新的

uid

为零

不要在触发器中将上下文信息设置为零。首先，你为什么要这么做？触发器不负责“清理”。merge语句将导致触发器分别为插入和更新执行。您没有注意到结果窗格中的多个“打印”吗？这应该是一个大线索

begin tran
declare @newid uniqueidentifier = newid()
-- 
set context_info @newid
print @newid;

with v as (select * from (values (1, 11), (2, 22), (6, 66)) v (id, x))
merge test as t using v on t.id = v.id
when matched then update set x = v.x
when not matched by target then insert (x) values (x);

SELECT * FROM dbo.testLog;
rollback
go