Cs166 Fake Solutions
1) A university database contains information about professors (identified by social
security number, or SSN), courses (identified by courseid), and semesters (identified by
semid). Professors teach courses during semesters, each of the following situations
concerns the Teaches relationship set. For each situation, draw an ER diagram that
describes it (assuming no further constraints hold).
a) Professors can teach the same course in several semesters, and each offering
must be recorded.
semid
Semesters
ssn courseid
N
Professors M teaches 1 Courses
b) Professors can teach the same course in several semesters, and only the most
recent such offering needs to be recorded. (Assume this condition applies in all
subsequent questions.)
semid
Semesters
ssn courseid
1
Professors M teaches 1 Courses
c) Every professor teaches exactly one course (no more, no less).
semid
Semesters
ssn courseid
1
Professors M teaches 1 Courses
d) Every professor teaches exactly one course (no more, no less), and every
course must be taught by some professor.
semid
Semesters
ssn courseid
1
Professors M teaches 1 Courses
2) Consider the following schema:
Suppliers( sid: integer, sname: string, address: string )
Parts( pid: integer, pname: string, color: string )
Catalog( sid: integer, pid: integer, cost: real )
Write the following queries in relational algebra.
Assume >< is the join symbol.
a) Find the names of suppliers who supply some red part.
( ( )
π sname π sid (π pidσ color =' red ' Parts ) >< Catalog >< Suppliers )
b) Find the sids of suppliers who supply some red or green part.
(
π sid π pid (σ color =' red 'or color =' green ' Parts ) >< Catalog )
c) Find the sids of suppliers who supply some red and some green part.
( (
ρ R1, π sid (π pid σ color =' red ' Parts ) >< Catalog ))
ρ ( R2, π ( (π sid pid σ color =' green ' Parts ) >< Catalog ) )
R1 ∩ R2
d) Find the sids of suppliers who supply every part.
(π sid , pid Catalog ) / (π pid Parts )
e) Find the sids of suppliers who supply every red or green part.
(π sid , pid Catalog ) / (π pid σ color =' red ' or color =' green ' Parts )
3) Consider the schema presented in problem 2. Write the following queries in SQL.
a) Find the name of every part.
SELECT P.pname
FROM Parts P
b) Find the pname and cost of all parts supplied by “BMI Supply”.
SELECT P.pname, C.cost
FROM Parts P, Catalog C, Suppliers S
WHERE S.sname=’BMI Supply’ and P.pid=C.pid and S.sid=C.sid
c) Find the sids of suppliers who supply some red and some green part.
SELECT C.sid
FROM Parts P, Catalog C
WHERE P.color=’red’ and P.pid=C.pid
and EXISTS ( SELECT P2.pid
FROM Parts P2, Catalog C2
WHERE P2.color=’green’ and C2.sid=C.sid
and P2.pid=C2.pid )
d) Find the sids of suppliers who only supply blue parts.
( ( SELECT C.sid
FROM Catalog C, Parts P
WHERE C.pid=P.pid and P.color=’blue’ )
EXCEPT
( SELECT C2.sid
FROM Catalog C2, Parts.P2
WHERE C2.pid=P.pid and P.color <> ‘blue’ ) )
e) Find the sids of suppliers who supply every part.
SELECT C.sid
FROM Catalog C
WHERE NOT EXISTS ( SELECT P.pid
FROM Parts P
WHERE NOT EXISTS ( SELECT C1.sid
FROM Catalog C1
WHERE C1.sid=C.sid
and C1.pid=P.pid ) )
OR
SELECT S.sid
FROM Suppliers S
WHERE NOT EXISTS ( ( SELECT P.pid
FROM Parts P )
EXCEPT
( SELECT C.pid
FROM Catalog C
WHERE C.sid=S.sid ) )
