Duplicate Enrollments

A student should not be able to enroll in the same course in the same semester twice — (student_id, course_id, semester) is meant to be a composite candidate key on enrollments, but it isn't enforced yet. Write a query returning student_id, course_id, semester, and a cnt column, for every combination that appears more than once.

sql
CREATE TABLE enrollments (
  student_id INTEGER NOT NULL,
  course_id INTEGER NOT NULL,
  semester TEXT NOT NULL
);

Sample data (this is what your query runs against when you press Run):

sql
INSERT INTO enrollments (student_id, course_id, semester) VALUES
(1, 101, 'Fall2025'),
(1, 102, 'Fall2025'),
(2, 101, 'Fall2025'),
(1, 101, 'Fall2025'),
(2, 102, 'Spring2026'),
(3, 101, 'Fall2025');