Exercise 1Relational Algebra

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6 Relations of Company

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Exercises

(a) Retrieve the names of employees in department 5 who work more than 10 hours per week on the 'ProductX' project.(b) List the names of employees who have a dependent with the same first name as themselves.(c) Find the names of employees that are directly supervised by 'Franklin Wong'. (d) For each project, list the project name and the total hours per week (by all employees) spent on that project.(e) Retrieve the names of employees who work on every project.

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Exercises(f) Retrieve the names of employees who do not work on any project.(g) For each department, retrieve the department name, and the average salary of

employees working in that department.(h) Retrieve the average salary of all female employees.(i) Find the names and addresses of employees who work on at least one project located in Houston but whose department has no location in Houston.List the last names of department managers who have no dependents.

(a) Retrieve the names of employees in department 5 who work more than 10 hours per week on the 'ProductX' project

Graphical approach can be used to help the logical and prosedural approach

Example of above query, the graphical approach: clue from query the relations that (may) work on the query are in the red text

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P

ProductX

Pname=‘ProductX’

W E

> 10

Hours > 10

Pnumber=Pno

5

Dno = 5

ESSN=SSN Fname, Lname (?)

WORKS_ON_ProductX (Rel.A) (PNAME=‘ProductX’(PROJECT) PNUMBER=PNO(WORKS_ON))

EMPLOYEE_DEPT5_WORKS_MORE_10_onProductX (Rel.B) ((EMPLOYEE) SSN=ESSN(HOURS>10(Rel.A)))

RESULT FNAME,LNAME(DNO=‘5’ (Rel.B))

List the names of employees who have a dependent with the same first name as themselves.

Graphical approach

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Dp EDepend_name=Fname Fname, Lname (?)

ESSN=SSN

RESULT FNAME,LNAME(DEPENDENT (ESSN,DEPEND_NAME)=(SSN,FNAME)(EMPLOYEE))

(c) Find the names of employees that are directly supervised by 'Franklin Wong'.

Graphical for next questions (try by Urself)

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E_SSN_FRANKLIN_WONG(Rel.A) (SSN(FNAME=‘FRANKLIN’ LNAME=‘WONG’(EMPLOYEE)))

E_SUPERVISED_BY_FRANKLIN_WONG (Result) (FNAME, LNAMES(EMPLOYEE) SUPERSSN=SSN(Rel.A))

(d) For each project, list the project name and the total hours per week (by all employees) spent on that project

Using function

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TOTAL_HOURS_PROJECT (Rel.A)

(PNOℱSUM HOURS(WORKS_ON))

RESULT (PNAME, TOT_HOURS(Rel.A) PNO=PNUMBER(PROJECT))

(e) Retrieve the names of employees who work on every project

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ALL_EMPLOYEE(SSN, PNO)(Rel.A) (SSN, PNO(WORKS_ON))

ALL_PROJECT(PNO)(Rel.B) (PNO(PROJECT))

E_ALL_PROJECT (Rel.A÷Rel.B)

RESULT (FNAME, LNAME (E_ALL_PROJECT * EMPLOYEE))

(f) Retrieve the names of employees who do not work on any project

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ALL_EMPLOYEE(SSN)(Rel.A) (SSN(EMPLOYEE))

ALL_EMPLOYEE_WORKING(SSN)(Rel.B) (ESSN(WORKS_ON))

E_NOT_WORKING (Rel.A - Rel.B)

RESULT (FNAME, LNAME ((EMPLOYEE) SSN=ESSN(E_NOT_WORKING))

(g) For each department, retrieve the department name, and the average salary of employees working in that department

(h) Retrieve the average salary of all female employees

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AVERAGE_SALARY_DEPARTMENT(Rel.A)

(DNOℱAVG SALARY(EMPLOYEE))

RESULT (DNO, AVG_SALARY(Rel.A * EMPLOYEE))

RESULT

ℱAVG SALARY(SEX=‘F’(EMPLOYEE))

(i) Find the names and addresses of employees who work on at least one project located in Houston but whose department has no location in Houston

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E_WORK_PROJ_IN_HOUSTON(Rel.A) (ESSN(WORKS_ON) PNO=PNUMBER(PLOCATION=‘HOUSTON’(PROJECT)))

E_D_NOT_IN_HOUSTON(Rel.B) (SSN(EMPLOYEE) DNO=DNUMBER(DLOCATION≠‘HOUSTON’(DEPARTMENT_LOCATIONS)))

RESULT (FNAME, LNAME, ADDRESS((EMPLOYEE) (Rel.A-Rel.B))

(j)List the last names of department managers who have no dependents

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D_MNG_SSN(Rel.A)(SSN(DEPARTMENT)

E_WITH_DEPENDENT(Rel.A)(SSN(DPENDENT)

MNGR_NO_DEPENDENT(Rel.A – Rel.B)

RESULT(LNAME(EMPLOYEE * MNGR_NO_DEPENDENT))