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**Relational Algebra and SQL Exercises**

Professor(ssn, profname, status) Course(crscode, crsname, credits) Taught(crscode, semester, ssn)

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Query 1 Return those professors who have taught ‘csc6710’ but never ‘csc7710’.

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**Relational Algebra Solution**

ssn(crscode=‘csc6710’(Taught))-ssn(crscode=‘csc7710’(Taught))

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**SQL Solution (SELECT ssn From Taught Where crscode = ‘CSC6710’) EXCEPT**

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Query 2 Return those professors who have taught both ‘csc6710’ and ‘csc7710’.

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**Relational Algebra Solution**

ssn(crscode=‘csc6710’(Taught)) ssn(crscode=‘csc7710’(Taught)),

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**SQL Solution SELECT T1.ssn From Taught T1, Taught T2,**

Where T1.crscode = ‘CSC6710’ AND T2.crscode=‘CSC7710’ AND T1.ssn=T2.ssn

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Query 3 Return those professors who have never taught ‘csc7710’.

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**Relational Algebra Solution**

ssn(Professor)-ssn(crscode=‘csc7710’(Taught)),

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**SQL Solution (SELECT ssn From Professor) EXCEPT From Taught T**

Where T.crscode = ‘CSC7710’)

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Query 4 Return those professors who taught ‘CSC6710’ or ‘CSC7710” but not both.

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**Relational Algebra Solution**

ssn(crscode<>‘csc7710’ crscode=‘csc7710’(Taught))-(ssn(crscode=‘csc6710’(Taught)) ssn(crscode=‘csc7710’(Taught)))

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**SQL Solution (SELECT ssn FROM Taught T**

WHERE T.crscode=‘CSC6710’ OR T.crscode=‘CSC7710’) Except (SELECT T1.ssn From Taught T1, Taught T2, Where T1.crscode = ‘CSC6710’) AND T2.crscode=‘CSC7710’ AND T1.ssn=T2.ssn)

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Query 5 Return those courses that have never been taught.

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**Relational Algebra Solution**

crscode(Course)-crscode(Taught)

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SQL Solution (SELECT crscode FROM Course) EXCEPT FROM TAUGHT )

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Query 6 Return those courses that have been taught at least in 10 semesters.

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**SQL Solution SELECT crscode FROM Taught GROUP BY crscode**

HAVING COUNT(*) >= 10

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Query 7 Return those courses that have been taught by at least 5 different professors.

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**SQL Solution SELECT crscode**

FROM (SELECT DISTINCT crscode, ssn FROM TAUGHT) GROUP BY crscode HAVING COUNT(*) >= 5

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Query 8 Return the names of professors who ever taught ‘CSC6710’.

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**Relational Algebra Solution**

profname(crscode=‘csc6710’(Taught) Professor)

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**SQL Solution SELECT P.profname FROM Professor P, Taught T**

WHERE P.ssn = T.ssn AND T.crscode = ‘CSC6710’

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Query 9 Return the names of full professors who ever taught ‘CSC6710’.

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**Relational Algebra Solution**

profname(crscode=‘csc6710’(Taught) status=‘full’(Professor))

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**SQL Solution SELECT P.profname FROM Professor P, Taught T**

WHERE P.status = ‘full’ AND P.ssn = T.ssn AND T.crscode = ‘CSC6710’

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Query 10 Delete those professors who never taught a course.

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**SQL Solution DELETE FROM Professor WHERE ssn NOT IN (SELECT ssn**

FROM Taught )

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Query 11 Change all the credits to 4 for those courses that are taught in f2006 semester.

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**SQL Solution UPDATE Course SET credits = 4 WHERE crscode IN (**

SELECT crscode FROM Taught WHERE semester = ‘f2006’ )

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Query 12 Return the names of the professors who have taught more than 30 credits of courses.

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**SQL Solution SELECT profname FROM Professor WHERE ssn IN (**

SELECT T.ssn FROM Taught T, Course C WHERE T.crscode = C.crscode GROUP BY T.ssn HAVING SUM(C.credits) > 30 )

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Query 13 List all the course names that professor ‘Smith” taught in Fall of 2007.

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**Relational Algebra Solution**

crsname(profname=‘Smith’(Professor) semester=‘f2007’(Taught) Course)

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**SQL Solution SELECT crsname FROM Professor P, Taught T, Course C**

WHERE P.profname = ‘Smith’ AND P.ssn = T.ssn AND T.semester = ‘F2007’ AND T.crscode = C.crscode

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Query 14 In chronological order, list the number of courses that the professor with ssn ssn = taught in each semester.

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**SQL Solution SELECT semester, COUNT(*) FROM Taught**

WHERE ssn = ‘ ’ GROUP BY semester ORDER BY semester ASC

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Query 15 In alphabetical order of the names of professors, list the name of each professor and the total number of courses she/he has taught.

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**SQL Solution SELECT P.profname, COUNT(*) FROM Professor P, Taught T**

WHERE P.ssn = T.ssn GROUP BY P.ssn, P.profname ORDER BY P.profname ASC

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Query 16 Delete those professors who taught less than 10 courses.

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**SQL Solution DELETE FROM Professor WHERE ssn IN( SELECT ssn**

FROM Taught GROUP BY ssn HAVING COUNT(*) < 10 )

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Query 17 Delete those professors who taught less than 40 credits.

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**SQL Solution DELETE FROM Professor WHERE ssn IN( SELECT T.ssn**

FROM Taught T, Course C WHERE T.crscode = C.crscode GROUP BY ssn HAVING SUM(C.credits) < 40 )

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Query 18 List those professors who have not taught any course in the past three semesters (F2006, W2007, F2007).

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**SQL Solution SELECT * FROM Professor P WHERE NOT EXISTS( FROM Taught**

WHERE P.ssn = T.ssn AND (T.semester = ‘F2006’ OR T.semester = ‘W2007’ OR T.semester=‘F2007’)) )

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