CREATE TABLE people_addresses (person_address_id NUMBER, person_id NUMBER, address_id NUMBER, date_from TIME, date_to TIME)
CREATE TABLE candidate_assessments (candidate_id NUMBER, qualification CLOB, assessment_date TIME, asessment_outcome_code CLOB)
CREATE TABLE people (person_id NUMBER, first_name CLOB, middle_name CLOB, last_name CLOB, cell_mobile_number CLOB, email_address CLOB, login_name CLOB, password CLOB)
CREATE TABLE students (student_id NUMBER, student_details CLOB)
CREATE TABLE student_course_registrations (student_id NUMBER, course_id NUMBER, registration_date TIME)
CREATE TABLE student_course_attendance (student_id NUMBER, course_id NUMBER, date_of_attendance TIME)
CREATE TABLE candidates (candidate_id NUMBER, candidate_details CLOB)
CREATE TABLE addresses (address_id NUMBER, line_1 CLOB, line_2 CLOB, city CLOB, zip_postcode CLOB, state_province_county CLOB, country CLOB)
CREATE TABLE courses (course_id CLOB, course_name CLOB, course_description CLOB, other_details CLOB)

What are the ids of the courses that are registered or attended by the student whose id is 121?
SELECT course_id FROM student_course_registrations WHERE student_id = 121 UNION SELECT course_id FROM student_course_attendance WHERE student_id = 121
SELECT "course_id" FROM "student_course_registrations" WHERE "student_id" = 121 UNION SELECT "course_id" FROM "student_course_attendance" WHERE "student_id" = 121