@@IDENTITY, SCOPE_IDENTITY(), OUTPUT and other methods of retrieving last identity

Question

I have seen various methods used when retrieving the value of a primary key identity field after insert.

declare @t table (
    id int identity primary key,
    somecol datetime default getdate()
)
insert into @t
default values

select SCOPE_IDENTITY() --returns 1
select @@IDENTITY --returns 1

Returning a table of identities following insert:

Create Table #Testing (  
    id int identity,  
    somedate datetime default getdate()  
)  
insert into #Testing  
output inserted.*  
default values   

What method is proper or better? Is the OUTPUT method scope-safe?

The second code snippet was borrowed from SQL in the Wild

Answer 1

It depends on what you are trying to do...

@@IDENTITY

Returns the last IDENTITY value produced on a connection, regardless of the table that produced the value, and regardless of the scope of the statement that produced the value. @@IDENTITY will return the last identity value entered into a table in your current session. @@IDENTITY is limited to the current session and is not limited to the current scope. For example, 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.

SCOPE_IDENTITY()

Returns the last IDENTITY value produced on a connection and by a statement in the same scope, regardless of the table that produced the value. SCOPE_IDENTITY() is similar to @@IDENTITY, but it will also limit the value to your current scope. 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.

IDENT_CURRENT()

Returns the last IDENTITY value produced in a table, regardless of the connection and scope of the statement that produced the value. IDENT_CURRENT is limited to a specified table, but not by connection or scope.