uniqueidentifier
SQL Primary Key - INT vs UniqueIdentifier
An identify value is an automatically incrementing integer that starts counting from a base seed value (such as 1, or 100, or 1000, whatever integer you choose), and increments by a value you specify, which is called an increment (such as 1, -1, 10, whatever integer you choose). The default seed is 1, and the default increment is 1. Because the values are never the same (they increment), an identify value often makes for a good column on which to base a primary key.
