Relational Model COP 4720 Lecture 9 Lecture Notes

Lecture 9COP Outline of Lecture Relational Algebra Queries Sec. 3.2

Lecture 9COP Summary of Relational Algebra (1) E ::= R | SELECT C (R) or  c (R) | PROJECT A 1,A 2,...,A n (R) or  A 1,A 2,...,A n (R) | E1 X E2 | E1 U E2 | E1 - E2 | RENAME R(A 1,A 2,...,A m ) (E) or  R(A 1,A 2,...,A m ) (E)

Lecture 9COP Summary of Relational Algebra (2) E ::= R | E1 JOIN E2 or E1 E2 | E1 JOIN C E2 or E1 C E2 | E1 INTERSECT E2 or E1  E2

Lecture 9COP Sample Schema for Exercises Student(ID, name, address, GPA, SAT) Campus(location, enrollment, rank) Apply(ID, location, date, major, decision)

Lecture 9COP Sample Queries PROJECT date,decision (Apply) Campus X Apply

Lecture 9COP Sample Queries Find Names and addresses of all students with GPA > 3.7 who applied to CS major and were rejected. List name and address of all students who didn’t apply anywhere.  name, address ((Students) Students.ID= Not_Apply.ID (  Not_Apply (  ID (Students) -  ID (Apply))))  name, address (  GPA>3.7  decision=‘No’  major=‘CS’ (Student Student.ID=Apply.ID Apply))

Lecture 9COP Schema for examples Employee(fname,lname,ssn,bdate,address,sex,salary,superssn,dno) Department(dname, dnumber,mgrssn,mgrstartdate) Dept_Locations(dnumber, dlocation) Project(pname,pnumber,plocation,dnum) Works_on(essn,pno,hours) Dependent(essn,dependent_name,sex,bdate,relationship)

Lecture 9COP Examples a)Retrieve the name and address of all employees who work for the ‘Research’ department. research   dname = ‘Research’ (Department) research_emps  research dnumber = dno (Employee) Result   fname,lname,address (research_emps) or research  Select dname = ‘Research’ (Department) research_emps  research join dnumber=dno Employee result  project fname,lname,address (research_emps)

Lecture 9COP Examples (refer to schema on previous slide) b) Retrieve the names of all employees in dept. 5 who work more than 10 hrs./week on project X. Option 1:  Fname,Lname (Employee SSN=ESSN (  Pname=‘Project X’  hours>10  Dnum=5 (Project Pnumber=Pno Works_On) ) ) Option 2: Emp_Work_X   Pname=‘Project X’ (Project Pnumber=Pno Works_On) Emp-Work_10  Employee SSN=ESSN (  hours>10 (Emp_Work_X) ) Result   Fname,Lname (  Dnum=5 (Emp_Work_10) )

Lecture 9COP c) List names of employees who have a dependent with the same first name. Same  (Employee) Fname=Dependent_Name (Dependent) Result   Fname,Lname (Same) ???????

Lecture 9COP c) List names of employees who have a dependent with the same first name. Same  (Employee) Fname=Dependent_Name  ssn=essn (Dependent) Result   Fname,Lname (Same)

Lecture 9COP d) Retrieve the names of employees who work on every project. Emp_proj  Project essn,pno ( Works_on ) T1  Project essn (Emp_proj) T2  Project pno (Works_on) T3  T2 x T1 T4  T3 – Emp_proj T5  Project essn T4 Ans  T1 – T5