The primary key is an assigned key that consists of a minimal set of attributes to uniquely specify an instance of a record. The attribute or a combination of attributes should meet the following characteristics:
- Unique: The attribute values of the key uniquely identify one instance of a concept. There are no duplicate instances.
- Non-volatile: The key does not change.
- Mandatory: All values are filled; there are no NULL values.
It is good practice to choose a primary key that also meet the following characteristic:
- Safe: Doesn't contain private or sensitive information, such as a social security number.