The IDENTITY property enables you to assign an auto-number to a numeric column.
Values for a column with an IDENTITY property are generated automatically.
The IDENTITY column must be of datatype int, bigint, smallint, tinyint, decimal, or numeric with a scale of 0.
It must be non-NULLable.
15.1.Identity
15.1.1.
Using the IDENTITY Property and the IDENTITY() Function