| Parent required? |
❌ No |
✔ Yes |
✔ Yes |
| Cascade delete |
Optional (checkbox) |
✔ Always |
✔ Always |
| Controls sharing/security |
Independent |
✔ Yes (inherits from Primary) |
❌ No |
| Controls ownership |
Child owns itself |
✔ Yes |
❌ No |
| Roll-Up Summary allowed? |
❌ No |
✔ Yes |
❌ No |
| Reparenting allowed? |
✔ Yes |
Optional |
Optional |
| How many M-D can object have? |
Unlimited (Lookups) |
1 (Primary of 2 possible M-D) |
1 (Secondary of 2 possible M-D) |
| Can be child of standard object? |
✔ Yes |
✔ Yes |
✔ Yes |
| Can be M-D child? |
Not applicable |
✔ Yes (custom objects only) |
✔ Yes (custom objects only) |
| Delete impact |
No impact unless enabled |
Deletes detail + its children |
Deletes detail + its children |
| Use case |
Optional relationship |
Main controlling parent |
Additional classification parent |
| Max number of child records |
Unlimited |
Unlimited (but roll-up performance degrades) |
Unlimited |
