SCOPE_IDENTITY, IDENT_CURRENT, and @@IDENTITY are similar functions because they return values that are inserted into identity columns. However, the scope and session on which last is defined in each of these functions differ:
- IDENT_CURRENT is not limited by scope and session; it is limited to a specified table. It returns the last identity value generated for a specific table in any session and any scope.
- @@IDENTITY returns the last identity value generated for any table in the current session, across all scopes.
- SCOPE_IDENTITY returns the last identity value generated for any table in the current session and the current scope.
Failed statements and transactions can change the current identity for a table and create gaps in the identity column values. The identity value is never rolled back even though the transaction that tried to insert the value into the table is not committed. For example, if an INSERT statement fails because of an IGNORE_DUP_KEY violation, the current identity value for the table is still incremented.
Examples
The following example shows the different identity values that are returned by IDENT_CURRENT, @@IDENTITY, and SCOPE_IDENTITY
USE test;
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.*/