The following table provides a brief comparison of PI and SI features.
| Feature | Primary | Secondary |
|---|---|---|
| Can be unique or nonunique | Both | Both |
| Affects row distribution | Yes | No |
| Create and drop dynamically | No | Yes |
| Improves access | Yes | Yes |
| Create using multiple data types | Yes | Yes |
| Requires separate physical structure | No | Yes, a subtable |
| Requires extra processing overhead | No | Yes |