The following table summarizes the differences between keys and indexes, using the primary key and primary index for purposes of comparison.
Primary Key | Primary Index |
---|---|
Important element of logical data model. | Not used in logical data model. |
Used to maintain referential integrity. | Used to distribute and retrieve data. |
Must be unique to identify each row. | Can be unique or nonunique. |
Values cannot change. | Values can change. |
Cannot be null. | Can be null. |
Does not imply access path. | Defines the most common access path. |
Not required for physical table definition. | Required for physical table definition. |