41. Composite primary key

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

Create an enrollment table where the same student cannot enroll in the same course twice.

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Answer & Explanation

4 Answers

Verified Correct Answer

Option A

CREATE TABLE enrollments (student_id BIGINT NOT NULL, course_id BIGINT NOT NULL, PRIMARY KEY (student_id, course_id));

Additional Explanation

Correct implementation. Prefer parameterized queries in application code, validate affected rows for UPDATE/DELETE, and use transactions for related writes.

Verified

Option B

PRIMARY KEY (student_id), PRIMARY KEY (course_id);

Additional Explanation

This option is incorrect for the stated requirement.

Verified

Option C

PRIMARY KEY (student_id, course_id, created_at) without needing created_at;

Additional Explanation

This option is incorrect for the stated requirement.

Verified

Option D

UNIQUE (student_id) only;

Additional Explanation

This option is incorrect for the stated requirement.