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Introduction to Relational Algebra and Calculus in Database Systems

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This document covers fundamental concepts of Relational Algebra and Relational Calculus as part of the CS 340 course at Prince Sultan College for Women. It presents various queries demonstrating how to manipulate and retrieve data from relational databases, including examples like listing employees with dependents, employees without dependents, and managers who have at least one dependent. Each query is explained with its corresponding notation and logic, enhancing understanding of relational database operations.

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Introduction to Relational Algebra and Calculus in Database Systems

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  1. Riyadh Philanthropic Society For Science Prince Sultan College For Woman Dept. of Computer & Information Sciences CS 340 Introduction to Database Systems Chapter 6: The Relational Algebra and Relational Calculus

  2. T1(SSN, NO_OF_DEPTS) ESSN COUNT DEPENDENT_NAME (DEPENDENT) T2  NO_OF_DEPS>1 (T1) RESULT pLNAME, FNAME (T2 * EMPLOYEE) • Examples of Queries in Relational Algebra • Query 5: list the names of all employees with two or more • dependents. Chapter 6: The Relational Algebra and Relational Calculus 42

  3. ALL_EMPS pSSN (EMPLOYEE) EMPS_WITH_DEPS(SSN) pESSN (DEPENDENT) EMPS_WITHOUT_DEPS (ALL_EMP - EMP_WITH_DEPS) RESULT pLNAME, FNAME (EMPS_WITHOUT_DEPS * EMPLOYEE) • Examples of Queries in Relational Algebra • Query 6: Retrieve the names of employees who have no dependents. Chapter 6: The Relational Algebra and Relational Calculus 43

  4. MGRS(SSN) pMGRSSN (DEPARTMENT) EMPS_WITH_DEPS(SSN) pESSN (DEPENDENT) MGRS_WITH_DEPS (MGRS EMPS_WITH_DEPS) RESULT pLNAME, FNAME (MGRS_WITH_DEPS * EMPLOYEE)  • Examples of Queries in Relational Algebra • Query 7: list the names of managers who have at least one • dependent.. Chapter 6: The Relational Algebra and Relational Calculus 44

  5. Example Queries Using Existential Quantifier • Query 3: find the name of each employee who works on some • project controlled by the department number 5. • Query 4: list the names of managers who have at least one • dependent. Q3: {e.LNAME, e.FNAME | EMPLOYEE(e) AND((x)(w) (PROJECT(x) AND WORKS_ON(w) AND x.DNUM=5 AND w.ESSN=e.SSN AND x.PNUMBER=w.PNO))} Q4: {e.LNAME, e.FNAME | EMPLOYEE(e) AND ((d) (p) (DEPARTMENT(d) AND DEPENDENT(p) AND e.SSN=d.MGRSSN AND p.ESSN=e.SSN))} Chapter 6: The Relational Algebra and Relational Calculus 49

  6. Example Queries Using Existential Quantifier • Query 5: find the names of employees who have no dependents. • Query 6: Make a list of project numbers for projects that involve an • employee whose last name is ‘Smith’, either as a worker or as a • manager of the controlling department for the project. Q5: {e.LNAME, e.FNAME | EMPLOYEE(e) AND (NOT (d) (DEPENDENT(d) AND e.SSN=d.ESSN))} Q6: {p.PNUMBER | PROJECT(p) AND (((e)(w) (EMPLOYEE(e) AND WORKS_ON(w) AND w.PNO=p.PNUMBER AND e.LNAME=‘Smith’ AND e.SSN=w.ESSN)) or ((m)(d)(EMPLOYEE(m) AND DEPARTMENT(d) AND p.DNUM=d.DNUMBER AND d.MGRSSN=m.SSN AND m.LNAME=‘Smith’)))} Chapter 6: The Relational Algebra and Relational Calculus 50

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