SQL Server 2000中，有三个比较类似的功能：他们分别是：SCOPE_IDENTITY、IDENT_CURRENT 和 @@IDENTITY，它们都返回插入到 IDENTITY 列中的值。

IDENT_CURRENT 返回为任何会话和任何作用域中的特定表最后生成的标识值。IDENT_CURRENT 不受作用域和会话的限制，而受限于指定的表。IDENT_CURRENT 返回为任何会话和作用域中的特定表所生成的值。
@@IDENTITY 返回为当前会话的所有作用域中的任何表最后生成的标识值。
SCOPE_IDENTITY 返回为当前会话和当前作用域中的任何表最后生成的标识值

SCOPE_IDENTITY 和 @@IDENTITY 返回在当前会话中的任何表内所生成的最后一个标识值。但是，SCOPE_IDENTITY 只返回插入到当前作用域中的值；@@IDENTITY 不受限于特定的作用域。


例如，有两个表 T1 和 T2，在 T1 上定义了一个 INSERT 触发器。当将某行插入 T1 时，触发器被激发，并在 T2 中插入一行。此例说明了两个作用域：一个是在 T1 上的插入，另一个是作为触发器的结果在 T2 上的插入。


假设 T1 和 T2 都有 IDENTITY 列，@@IDENTITY 和 SCOPE_IDENTITY 将在 T1 上的 INSERT 语句的最后返回不同的值。


@@IDENTITY 返回插入到当前会话中任何作用域内的最后一个 IDENTITY 列值，该值是插入 T2 中的值。


SCOPE_IDENTITY() 返回插入 T1 中的 IDENTITY 值，该值是发生在相同作用域中的最后一个 INSERT。如果在作用域中发生插入语句到标识列之前唤醒调用 SCOPE_IDENTITY() 函数，则该函数将返回 NULL 值。


而IDENT_CURRENT('T1') 和 IDENT_CURRENT('T2') 返回的值分别是这两个表最后自增的值。


注意@@IDENTITY是当前会话
所以并发不会影响这个取值

其它还有@@ROWCOUNT @@ERROR 也类似。

在一般的批处理或存储过程中，最常用也比较保险的还是SCOPE_IDENTITY函数，尤其在处理流程中涉及触发器的情形。

这有篇Doug Seven在《10 Things You Shouldn't Do with SQL Server》提到的
http://www.dotnetjunkies.com/Article/86F0988E-FED4-414F-BA2E-D01D953C11BE.dcik
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9. @@IDENTITY vs. SCOPE_IDENTITY
This particular issue isn't so much about doing something right or wrong, it is about understanding your options so you choose the right one. Both @@IDENTITY and SCOPE_IDENTITY() return the last identity value (primary key) that was entered by your active session, but in different scenarios they can each return different values. When I say "active session" I am referring to the current activity you are engaging in. For example, if you can a stored procedure, that is what I am referring to as your active session. Each call to t a stored procedure (or user defined function, etc) is a session, unless the a stored procedure is nested in the stored procedure you are calling. In the case of a nested stored procedure or user defined method, while they are separate methods, they are part of the current session, but not part of the current scope. Your scope is limited to the method (stored procedure or user defined function) that you explicitly invoked. This is where the difference between @@IDENTITY and SCOPE_IDENTITY() comes in.

@@IDENTITY will return the last identity value entered into a table in your current session (this is limited to your session only, so you won't get identities entered by other users). While @@IDENTITY is limited to the current session, it is not limited to the current scope. In other words, if you have a trigger on a table that causes an identity to be created in another table, you will get the identity that was created last, even if it was the trigger that created it. Now this isn't bad, as long as you ensure that things are done in the correct order. Where this can get ugly is when there is an application revision and a new trigger gets added that gets fired from your stored procedure. Your code didn't anticipate this new trigger, so you could now be getting an incorrect value back.

SCOPE_IDENTITY(), like @@IDENTITY, will return the last identity value created in the current session, but it will also limit it to your current scope as well. In other words, it will return the last identity value that you explicitly created, rather than any identity that was created by a trigger or a user defined function.

Follow is some sample script that you can run to see the different value you get back before a trigger is added, and after.
=================================================
/*In a test database, create a new table named TY*/
USE SomeTestDatabase
CREATE TABLE TABLE_A ( TABLE_A_id int IDENTITY(100,5)PRIMARY KEY, ItemValue varchar(20) NULL)
/*INSERT records into TABLE_A*/
INSERT TABLE_A VALUES ('Widget')
INSERT TABLE_A VALUES ('Boat')
INSERT TABLE_A VALUES ('Car')
GO

/*Create a new table named TABLE_B*/
CREATE TABLE TABLE_B ( TABLE_B_id int IDENTITY(1,1)PRIMARY KEY, Username varchar(20) NOT NULL)
/*INSERT records into TABLE_B*/
INSERT TABLE_B VALUES ('Doug')
INSERT TABLE_B VALUES ('Erika')
INSERT TABLE_B VALUES ('Lola')
GO

/*INSERT a record into TABLE_B*/
INSERT TABLE_B
VALUES ('Kali')

/*SELECT the data to see what values were returned by @@IDENTITY and SCOPE_IDENTITY()*/
SELECT * FROM TABLE_A
SELECT * FROM TABLE_B
SELECT @@Identity AS [@@Identity], SCOPE_IDENTITY() AS [SCOPE_IDENTITY]
GO

/*Create the trigger that inserts a row in table TABLE_A when a row is inserted in table TABLE_B*/
CREATE TRIGGER TABLE_B_trig
ON TABLE_B
FOR INSERT AS
BEGIN
INSERT TABLE_A VALUES ('Airplane')
END
GO

/*Now INSERT a record into TABLE_B, which will cause the trigger to be fired*/
INSERT TABLE_B
VALUES ('Donny')

/*SELECT the data to see what values were returned by @@IDENTITY and SCOPE_IDENTITY() - they will be different values. SCOPE_IDENTITY() will return the identity from TABLE_A (the identity that you explicitly created), while @@IDENTITY will return the identity from TABLE_B (the triggered item).*/
SELECT * FROM TABLE_A
SELECT * FROM TABLE_B
SELECT @@Identity AS [@@Identity], SCOPE_IDENTITY() AS [SCOPE_IDENTITY]
GO


http://blog.joycode.com/ghj/archive/2004/03/21/16745.aspx