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 (student_id VARCHAR)
TABLE: CREATE TABLE student_course_registrations (student_id VARCHAR)

### Question ###
What are the id of students who registered courses or attended courses?

### Accurate SQL ###

SELECT student_id FROM student_course_registrations UNION SELECT student_id FROM student_course_attendance