Context: CREATE TABLE Student_Course_Enrolment (student_id VARCHAR); CREATE TABLE Students (personal_name VARCHAR); CREATE TABLE Students (personal_name VARCHAR, student_id VARCHAR)
Question: Find the personal names of students not enrolled in any course.
Answer: SELECT personal_name FROM Students EXCEPT SELECT T1.personal_name FROM Students AS T1 JOIN Student_Course_Enrolment AS T2 ON T1.student_id = T2.student_id