Write SQL expression for the following questions about the security aspects of above database.
1. Student can view all the information in the course and instructor tables except for InstructorId.
2. Student can also view the courseno, semester, year, location and instructor name(not instructorid) of all courses that are being offered.
3. Instructor, ‘ProfShekhar' can view enrollment info(ssn, courseno, semester, year, grade) of students who are in his classes but only change the grade.