CREATE TABLE Students (personal_name VARCHAR)
CREATE TABLE Student_Course_Enrolment (student_id VARCHAR)

Find the personal names of students not enrolled in any course.
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
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"