Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table. Often this is the primary key field that we would like to be created automatically every time a new record is inserted.

Is identity column a primary key?

In many cases an identity column is used as a primary key; however, this is not always the case. It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to enforce uniqueness on the column you must include the appropriate constraint too.

Is auto increment a constraint?

The Auto increment is commonly used to generate primary keys. ... It is considered a good practice to specify the unsigned constraint on auto increment primary keys to avoid having negative numbers. When a row is deleted from a table, its auto incremented id is not re-used.