比较 IDENT_CURRENT、@@IDENTITY 和 SCOPE_IDENTITY 返回的标识值

SELECT @@IDENTITY;
/*
针对当前会话,所有作用域
Returns the value 100. This was inserted by the trigger.*/

SELECT SCOPE_IDENTITY();
/* 
针对当前会话,当前作用域
Returns the value 1. This was inserted by the 
INSERT statement two statements before this query.*/

SELECT IDENT_CURRENT('t7');
/* 
针对全局会话
Returns value inserted into t7, that is in the trigger.*/

SELECT IDENT_CURRENT('t6');
/* 
针对全局会话
Returns value inserted into t6. This was the INSERT statement four statements before this query.*/

其实自己试试就明白了,完整的代码如下:

USE AdventureWorks2008R2;
GO
IF OBJECT_ID(N't6', N'U') IS NOT NULL 
    DROP TABLE t6;
GO
IF OBJECT_ID(N't7', N'U') IS NOT NULL 
    DROP TABLE t7;
GO
CREATE TABLE t6(id int IDENTITY);
CREATE TABLE t7(id int IDENTITY(100,1));
GO
CREATE TRIGGER t6ins ON t6 FOR INSERT 
AS
BEGIN
   INSERT t7 DEFAULT VALUES
END;
GO
--End of trigger definition

SELECT id FROM t6;
--IDs empty.

SELECT id FROM t7;
--ID is empty.

--Do the following in Session 1
INSERT t6 DEFAULT VALUES;
SELECT @@IDENTITY;
/*Returns the value 100. This was inserted by the trigger.*/

SELECT SCOPE_IDENTITY();
/* Returns the value 1. This was inserted by the 
INSERT statement two statements before this query.*/

SELECT IDENT_CURRENT('t7');
/* Returns value inserted into t7, that is in the trigger.*/

SELECT IDENT_CURRENT('t6');
/* Returns value inserted into t6. This was the INSERT statement four statements before this query.*/

-- Do the following in Session 2.
SELECT @@IDENTITY;
/* Returns NULL because there has been no INSERT action 
up to this point in this session.*/

SELECT SCOPE_IDENTITY();
/* Returns NULL because there has been no INSERT action 
up to this point in this scope in this session.*/

SELECT IDENT_CURRENT('t7');
/* Returns the last value inserted into t7.*/

参考:http://msdn.microsoft.com/zh-cn/library/ms175098(SQL.105).aspx