Question

I’m currently working on the following homework:

CREATE TABLE T_1
(COURSE_NO CHAR(8) PRIMARY KEY,
COURSE_NAME CHAR(50) );

CREATE TABLE T_2
(COURSE_NO CHAR(8),
COURSE_NAME CHAR(50) );

CREATE TABLE T_3
(COURSE_NO CHAR(8),
STUDENT_ID CHAR(15),
GRADE CHAR (2));

INSERT INTO T_1
VALUES
('CS100','Data Structures'),
('CS200','Object Oriented Programming'),
('CS300','Distributed Systems'),
('EE100','Circuit Analysis'),
('EE200','VLSI Design'),
('EE300','Packet Switching Networks');

INSERT INTO T_2
VALUES
('EE100','Circuit Analysis'),
('EE200','VLSI Design'),
('EE300','Packet Switching Networks'),
('MA100','Calculus'),
('MA200','Advanced Calculus'),
('MA300','Number Theory');

INSERT INTO T_3
VALUES
('CS100','150-70-5879','B'),
('CS100','280-90-8766','A'),
('EE100','430-76-6858','B'),
('CS200','720-60-5000','B');

I’m requested to specify the tuples given: (T1 – T2) union (T2 – T1) Union (T1 intersect T2).

Now I know that MySQL uses the, either join for the minus operator, I’m able to process each minus in their own way like:

SELECT *
FROM T_1
LEFT JOIN T_2
ON T_1.Course_No = T_2.Course_no
WHERE T_2.Course_no IS NULL;

I can also do this for the T2 – T1 but I’m lost when it comes to doing it all in 1 query or how to (T1-T2) U (T2-T1) or (T2-T1) U (T1nT2).

Any help?

Answer 1

Not best, but very intuitive way:

q1 = (T1 - T2): (SELECT course_no FROM T_1
                 WHERE course_no NOT IN (SELECT course_no FROM T_2))
q2 = (T2 - T1): same way, change T_1 and T_2
q3 = (T1 intersect T2): (SELECT course_no FROM T_1
                         WHERE course_no IN (SELECT course_no FROM T_2))

answer = q1 union q2 union q3

We get following sql-query:

(SELECT course_no FROM T_1 WHERE course_no NOT IN (SELECT course_no FROM T_2))
UNION
(SELECT course_no FROM T_2 WHERE course_no NOT IN (SELECT course_no FROM T_1))
UNION
(SELECT course_no FROM T_1 WHERE course_no IN (SELECT course_no FROM T_2))

What is about T_3?

EDIT:

T_1 = CS100, CS200, CS300, EE100, EE200, EE300
T_2 = EE100, EE200, EE300, MA100, MA200, MA300

q1 = T_1 - T_2 = CS100, CS200, CS300
q2 = T_2 - T_3 = MA100, MA200, MA300
q3 = T_1 intersect T_2 = EE100, EE200, EE300

answer = q1 union q2 union q3 = CS100, CS200, CS300, MA100, MA200, MA300, EE100, EE200, EE300