Using the relations below, write relational algebra queries for the following.
relations: Courses(cnum,title,credits), Professors(pid,pname,dept), Teaches(pid,cnum,semester)
(a) Find the names and departments of professors who taught at least one course in Fall2011.
(b) Find the titles of courses taught by the professors of Computer Science department.
(c) Find the course numbers that were taught in Fall2011 but not in Spring2012.
(d) Find the departments that have at least two professors.
Solution
create table courses
cnum INT PRIMARY KEY,
title VARCHAR(20) NOT NULL UNQUINE,
credits INT NOT NULL
create table professors
pid INT PRIMARY KEY,
pname VARCHAR(20) NOT NULL,
dept VARCHAR(10) NOT NULL
create table Teaches
pid INT,
cnum INT,

semster VARCHAR(9),
FOREIGNKEY(cnum) REFERENCE course (cnum)
FOREIGNKEY (pid) REFERENCE professor (pid)
COURSES:
PROFESSORS:
TEACHES:
a) name,dept( dept="CS" (professorsteachescourses)
b) title ( dept="CS" (professorscourses)
c) T1 cnum ( semesterspring2012 (coursesteaches)
T2 cnum ( semester=fall2011 (coursesteaches)
T1-T2
d) (R1.professors)
(R2.professors)
R1.deptR1.dept=R2.pnameR1.pnameR2.pname(R1XR2)
cnum title credits
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