The following table compares PKs and PIs.
| Primary Key | Primary Index |
|---|---|
| Identifies a row uniquely. | Distributes rows. |
| Does not imply access path. | Defines most common access path. |
| Must be unique. | May be unique or nonunique. |
| Cannot be null. | May be null. |
| Causes a Unique Primary Index (UPI) or Unique Secondary Index (USI) to be created. | N/A |
| Constraint that ensures referential integrity. | Physical access mechanism. |
| Required only if Vantage is to perform referential integrity checks. | Defined for most production tables. Omitted for some staging tables. |
| If Vantage performs referential integrity checks, column limit is 64. Otherwise, there is no arbitrary column limit. | 64-column limit. |
| Do not change values. | You can change values. |