What is the difference between Scope_Identity(), Identity(), @@Identity, and Ident_Current()?

Question

I know Scope_Identity(), Identity(), @@Identity, and Ident_Current() all get the value of the identity column, but I would love to know the difference.

Part of the controversy I'm having is what do they mean by scope as applied to these functions above?

I would also love a simple example of different scenarios of using them?

Answer 1

• The @@identity function returns the last identity created in the same session.
• The scope_identity() function returns the last identity created in the same session and the same scope.
• The ident_current(name) returns the last identity created for a specific table or view in any session.
• The identity() function is not used to get an identity, it's used to create an identity in a select...into query.

The session is the database connection. The scope is the current query or the current stored procedure.

A situation where the scope_identity() and the @@identity functions differ, is if you have a trigger on the table. If you have a query that inserts a record, causing the trigger to insert another record somewhere, the scope_identity() function will return the identity created by the query, while the @@identity function will return the identity created by the trigger.

So, normally you would use the scope_identity() function.

Answer 2

Good question.

• @@IDENTITY: returns the last identity value generated on your SQL connection (SPID). Most of the time it will be what you want, but sometimes it isn't (like when a trigger is fired in response to an INSERT, and the trigger executes another INSERT statement).

• SCOPE_IDENTITY(): returns the last identity value generated in the current scope (i.e. stored procedure, trigger, function, etc).

• IDENT_CURRENT(): returns the last identity value for a specific table. Don't use this to get the identity value from an INSERT, it's subject to race conditions (i.e. multiple connections inserting rows on the same table).

• IDENTITY(): used when declaring a column in a table as an identity column.

For more reference, see: http://msdn.microsoft.com/en-us/library/ms187342.aspx.

To summarize: if you are inserting rows, and you want to know the value of the identity column for the row you just inserted, always use SCOPE_IDENTITY().