Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE student_course_registrations (student_id VARCHAR)
### Question:
what is id of students who registered some courses but the least number of courses in these students?
### Answer:
SELECT student_id FROM student_course_registrations GROUP BY student_id ORDER BY COUNT(*) LIMIT 1