Write following SQL statements according to given database model.

a$-)$ write a check constraints whether the value of student.tot$\_$cred is equal to the sum of the

course.credits of the courses taken by each student.

b$-)$ Retrieve the names of instructors and their students advised by that instructor in the order of

advisor name and student name.

c$-)$ For each semester and year, list the number of courses and the number of sections given.

d$-)$ List the courses taken by the students if these courses are given by the advisor of that student.