DATABASE SCHEMA

Professor(ssn, profname, status, salary) (PRIMARY KEY ssn)

Course(crscode, crsname, credits) (PRIMARY KEY crscode)

Taught(crscode, semester, ssn) (PRIMARY KEY crscode)

Assumptions: (1) Each course has only one instructor in each semester; (2) all professors have different salaries; (3) all professors have different names; (4) all courses have different names; (5) status can take values from Full, Associate, and Assistant.

Please write SQL command for the followings:

a. Return those courses crscode that have been taught by at least 5 different professors.

b. In chronological order, list the number of courses that the professor with ssn = 123456789 taught in each semester.

c. For each professor, return the total number of credits that she/he taught for all semesters. (Hint: return ssn for the professor)