Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE student_course_attendance (course_id VARCHAR, student_id VARCHAR)
TABLE: CREATE TABLE student_course_registrations (course_id VARCHAR, student_id VARCHAR)

### Question ###
Find the id of courses which are registered or attended by student whose id is 121?

### Accurate SQL ###

SELECT course_id FROM student_course_registrations WHERE student_id = 121 UNION SELECT course_id FROM student_course_attendance WHERE student_id = 121