CODEWITHSUNDEEP
sqlrelational-algebra
user2976568
user2976568

Reputation: 149

translating SQL query to Relational Algebra

I have to translate an SQL query to relational algebra in a specific way but im not sure if my answer is a correct one.

Database

Students: (studentID, firstname, familyname, address, borough)
Entries: (studentID, examID< result)
Exams: (examID, examName, qualification, board, date)

SQL query

SELECT studentID
FROM Students s, Entries e, Exams x
WHERE s.studentID = e.studentID AND e.examID = x.examID AND 
s.borough='Haringey' AND e.result = 'pass' AND x.examName='Latin'

I have to re-express this query in relational algebra where the joins are performed on the tables after the tables have been reduced by the selection operators

my answer

PROJECTstudentID(SELECTs.borough='Haringey'(Students)) EQUIJOIN s.studentID=e.studentID((SELECTe.result='pass'(Entries)) EQUIJOIN e.examID=x.examID (SELECTx.examName='Latin'(Exams)))

Upvotes: 0

Views: 270

Answers (1)

Renzo
Renzo

Reputation: 27424

Your query is correct. You have “pushed” all the select operation correctly. Note that you could also project the result of each select to the minimun number of attributes required by the following operators.

Upvotes: 1

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