INSERT INTO users (firstName, lastName, email )
VALUES ( '#FORM.LastName#', '#FORM.LastName#', '#FORM.email#' );

select thisID = @@identity

----------------------------------------------------------------------

The primary key is then referenced as Q_QueryName.thisID

"thisID" can be renamed to whatever you like

I use this code in ColdFusion, I assume it works in any language that supports SQL querying.

Get Primary Key ID after an INSERT

SQL