Thursday, December 21, 2006

Difference between @@IDENTITY and SCOPE_IDENTITY()

A colleague asked me today if he could use @@IDENTITY in the context of an insert stored procedure to return the generated value for an identity column. I recalled there was something about this function so I consulted the Books OnLine.
It states :

@@IDENTITY, SCOPE_IDENTITY, and IDENT_CURRENT are similar functions because they all return the last value inserted into the IDENTITY column of a table.

@@IDENTITY and SCOPE_IDENTITY return the last identity value generated in any table in the current session. However, SCOPE_IDENTITY returns the value only within the current scope; @@IDENTITY is not limited to a specific scope.

It took me a minute to find a good example to illustrate the difference between the two, but with a trigger I created the following example:

USE TempDB
GO
CREATE TABLE tst
( a int identity(1,1), s varchar(10))
GO
CREATE TABLE tst2
( a int identity(1000,1), s varchar(10))
GO
CREATE TRIGGER dbo.trgTst
ON tst
AFTER INSERT
AS INSERT tst2 SELECT inserted.s FROM inserted
GO
INSERT tst VALUES('a')
SELECT
@@IDENTITY AS [@@IDENTITY],
SCOPE_IDENTITY() AS [SCOPE_IDENTITY()]
GO
DROP TABLE tst2
DROP TABLE tst

SCOPE_IDENTITY() will give you the value of tst.$IDENTITY, ignoring the identity value that is generated for table tst2 with the trigger after the insert into tst. @@IDENTITY will give you that value from tst2.$IDENTITY.

So the function we actually need in our case is not @@IDENTITY but SCOPE_IDENTITY().

1 comment:

रुपेश कुमार तिवारी said...

good example but still not much clear try to give some more simple examples