a. Find courses (dcode, cno) that do not have prerequisites

b. Find courses (dcode, cno) that do have some prerequisites

Consider the following University Database schemas. Primary keys are underlined. Relational Schemas department (dcode, dname, chair) course (dcode, cno, title, units) prereq (dcode, cno, pcode, pno) class (class, dcode, cno, instr) Meaning and additional information Department identified by dcode is named dname and has department chair with ssn chair (this ssn must appear in the table faculty below) Course identified by (dcode,cno) has title and units (e.g., 3 units/credits) Course (dcode, cno) has a prerequisite course (pcode, pno) Class identified by class id is offered by department dcode, has course number cno, and is taught by instructor with ssn instr (this ssn must appear in the table faculty below) Faculty identified by ssn has a name and rank, and belongs to department dcode (which must appear in the table department) Student identified by ssn has a name, major and status. Student identified by ssn is enrolled in the class identified by class no (ssn must appear in the table student, and class must appear in the table class) Student identified by ssn took the course identified by (dcode, cno) and received the grade. Assume that the only grades available are A, B, C and F. faculty (ssn, name, dcode, rank) student (ssn, name, major, status) enrollment (class, ssn) transcript (dcode, cno, ssn, grade) Implement the following queries using: A. Tuple relational calculus B. Relational algebra C. SQL