@@identity
я бы не советовал таким образом определять
а вот так:

MystеryА в чём разница, почему не советовал бы?
все ответы в BOL:

BOL @@IDENTITY
Returns the last-inserted identity value.
If the statement fires one or more triggers that perform inserts that generate identity values, calling @@IDENTITY immediately after the statement returns the last identity value generated by the triggers

SCOPE_IDENTITY
Returns the last IDENTITY value inserted into an IDENTITY column in the same scope. A scope is a module -- a stored procedure, trigger, function, or batch. Thus, two statements are in the same scope if they are in the same stored procedure, function, or batch.

вот так вот