Describe the relationship between Enrolls and STUDENT

Question

BlackTom AI · Accepted Answer

suniqueID in Enrolls is both a primary key component and a foreign key referencing STUDENT.suniqueID, so each Enrolls row must point to exactly one STUDENT.

1) Relevant concepts
- Primary key (PK): uniquely identifies a row and cannot be null. Enrolls has suniqueID as part of its PK.
- Foreign key (FK): enforces a reference to a row in another table. suniqueID in Enrolls references STUDENT.suniqueID.
- Cardinality/participation: whether the FK can be null (optional) or must exist (mandatory) determines 0..1 vs 1..1 etc.

2) Step-by-step reasoning
- Inspect Enrolls table: its PK is composite (suniqueID, cnumber). Because suniqueID is part of the PK, it cannot be NULL for any Enrolls row.
- suniqueID in Enrolls points to STUDENT.suniqueID (a FK relationship). Referential integrity requires that the referenced STUDENT row exists.
- Therefore every single Enrolls tuple must be associated with a STUDENT tuple, and there is exactly one STUDENT referenced per Enrolls row (a FK column holds a single value).

3) Intermediate logic steps (explicit)
- Enrolls.suniqueID is non-null (PK constraint) → no Enrolls row can lack a student reference.
- The FK links to one STUDENT.suniqueID → one referenced student per Enrolls row.
- Combine: exactly one STUDENT per Enrolls row.

4) Why the correct answer is correct
Because the FK column in Enrolls is mandatory (it is part of the PK), cardinality from a single Enrolls record to STUDENT is 1 and only 1.

5) Why other options are incorrect (brief)
- "0 to 1 Student": incorrect because suniqueID is part of PK so it cannot be null (not optional).
- "1 to Many Students", "Many Students", "Many Enrolls are associated with Many Students": wrong direction or imply an Enrolls row can reference multiple students, which is impossible for a single FK field.
- Options saying "0 to Many" or "There is not a relationship": contradict the FK/PK shown.

Conclusion: The correct relationship description is "1 Enrolls is associated with 1 and only 1 Student," which matches the provided answer.

Describe the relationship between Enrolls and STUDENT单项选择题

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