text: CREATE TABLE student_course_attendance (student_id VARCHAR); CREATE TABLE student_course_registrations (student_id VARCHAR) -- What are the id of students who registered courses or attended courses? SELECT student_id FROM student_course_registrations UNION SELECT student_id FROM student_course_attendance CREATE TABLE student_course_attendance (course_id VARCHAR, student_id VARCHAR); CREATE TABLE student_course_registrations (course_id VARCHAR, student_id VARCHAR) -- Find the id of courses which are registered or attended by 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 CREATE TABLE student_course_attendance (student_id VARCHAR); CREATE TABLE student_course_registrations (student_id VARCHAR) -- What are all info of students who registered courses but not attended courses? SELECT * FROM student_course_registrations WHERE NOT student_id IN (SELECT student_id FROM student_course_attendance) CREATE TABLE student_course_registrations (student_id VARCHAR, course_id VARCHAR, registration_date VARCHAR); CREATE TABLE courses (course_id VARCHAR, course_name VARCHAR) -- List the id of students who registered course statistics in the order of registration date. SELECT T2.student_id FROM courses AS T1 JOIN student_course_registrations AS T2 ON T1.course_id = T2.course_id WHERE T1.course_name = "statistics" ORDER BY T2.registration_date