Consider the university enrollment database schema:
Student(snum: integer, sname: string, major: string, level: string, age: integer)
Class(name: string, meets at: time, room: string, fid: integer)
Enrolled(snum: integer, cname: string)
Faculty(fid: integer, fname: string, deptid: integer)
The meaning of these relations is straightforward; for example, Enrolled has one record per student-class pair such that the student is enrolled in the class.
For each of the following transactions, state the SQL isolation level you would use and explain why you chose it.
1. Enroll a student identified by her snum into the class named 'Introduction to Database Systems'.
2. Change enrollment for a student identified by her snum from one class to another class.
3. Assign a new faculty member identified by his fid to the class with the least number of students.
4. For each class, show the number of students enrolled in the class.