The following table compares PI and SI features.
| Feature | Primary Index | Secondary Index |
|---|---|---|
| Can be unique or nonunique | Yes | Yes |
| Affects row distribution | Yes | No |
| Can be created and dropped dynamically | No | Yes |
| Improves access | Yes | Yes |
| Can be created using multiple data types | Yes | Yes |
| Requires separate physical structure | No | Yes, a subtable |
| Requires extra processing overhead | No | Yes |