Find the id of courses which are registered or attended by student whose id is 121?
CREATE TABLE student_course_attendance (course_id VARCHAR, student_id VARCHAR); CREATE TABLE student_course_registrations (course_id VARCHAR, student_id VARCHAR)
[SQL] SELECT course_id FROM student_course_registrations WHERE student_id = 121 UNION SELECT course_id FROM student_course_attendance WHERE student_id = 121 [/SQL]