Lookup relationship is an example of loosely coupled relationship whereas Master-Detail is an example of Tightly coupled relationship.
- In tightly coupled (M-D relation) when we delete the parent record, all child records are also deleted but nothing of this sort happens in loosely coupled (Lookup relation). Sure shot ADM 201,CON 201, DEV 401 question.
- In M-D relation, a person who can view the master can see all the detail records of that master as the their is no owner on the detail side records and detail side gets its access properties from the master. Nothing of this sort happens in the Lookup relation as both objects have owners.
- Roll up summary field can be made on Master Detail relation but not on the Lookup relationship.
- One detail side record can have maximum 2 masters but no limit on the Lookup fields. DEV 401 certification question.
- Standard objects can never be on the detail side of the master detail relationship but no such thing in a Lookup relation. (ADM 201)