University of Waterloo Midterm Examination

Transcription

1 University of Waterloo Midterm Examination Winter, 2007 Student Name: Student ID Number: Section: Course Abbreviation and Number CS 348 Course Title Introduction to Database Management Sections 01 (11:30), 02 (14:30) Instructor A. Aboulnaga Date of Exam March 6, 2007 Exam Returned March 8, 2007 Appeal Deadline March 22, 2007 Time Period 19:00-21:00 Duration of Exam Number of Exam Pages (including this cover sheet) Exam Type Additional Materials Allowed 2 hours 12 pages Closed Book None NOTE: KEEP YOUR ANSWERS AS CONCISE AS POSSIBLE. Question 1: Question 3: Question 5: (19 marks) (24 marks) (16 marks) Question 2: Question 4: (24 marks) (17 marks) Total: (100 marks) CS348 1 of 12

2 Question 1. (19 marks) a. (6 marks) Define the terms candidate key, primary key, and foreign key. Be concise. b. (4 marks) Consider the following instance of relation R(a, b, c). Based on this instance, which of the three attributes of R can you infer is a candidate key? Which of the three attributes can you infer is not a candidate key? Justify your answer. a b c CS348 2 of 12

3 c. (4 marks) What is data independence? Describe the two types of data independence. d. (5 marks) Consider the following query expressed in the domain relational calculus: Is this query safe? Justify your answer. { x y(r y S x, y )} CS348 3 of 12

4 Question 2. (24 marks) The following schema is used for questions 2, 3, and 4. Primary key and foreign key constraints are illustrated in the schema diagram. For the purposes of this exam, assume that all attributes are defined to be NOT NULL. Department DeptNo Project ProjNo DeptNo RespEmp MajProj Emp_Act EmpNo ProjNo ActNo EmStDate EmEndDate EmPTime DeptName MgrNo AdmrDept Employee EmpNo FirstName MidInit LastName WorkDept HireDate Salary CS348 4 of 12

5 a. (8 marks) Write a single relational algebra query that is equivalent to the SQL query below. select DeptNo from Department where exists (select * from Employee E where E.WorkDept = D.DeptNo and not exists (select * from Emp_Act A where A.EmpNo = E.EmpNo)) In your relational algebra query, use D, E, and A to represent the Department, Employee, and Emp Act tables, respectively. b. (8 marks) Write a query in the domain relational calculus that is equivalent to the query from part (a) of this question. CS348 5 of 12

6 c. (8 marks) Consider the following domain relational calculus query: { D D1, N, M, A(Department D1, N, M, A D = D1 P, D2, R, J(Project P, D2, R, J D = D2 E, F, I, L, D3, H, S(Employee E, F, I, L, D3, H, S D = D3)))} Express this query using relational algebra. CS348 6 of 12

7 Question 3. (24 marks) a. (8 marks) Write an SQL DML statement that will increase the salaries of all department managers by 10%. (If an employee manages more than one department, their salary should be increased by a total of 10%, not 10% per department.) b. (8 marks) Write an SQL query that returns the department numbers and names of the departments that have at least 5 employees. (If there are k such departments, the query result should contain k tuples.) CS348 7 of 12

8 c. (8 marks) The Employee table gives (as the value of the HireDate attribute) the hiring date of each current employee of the company. Write a single SQL query that will return, for each year in which at least one employee was hired, the cumulative total number of (current) employees that had been hired by the end of that year. For example, if three of the current employees were hired in 2003, none were hired in 2004, two were hired in 2005, and one was hired in 2006, your query result should contain these tuples: The query result should be sorted in increasing order of year, as shown in the example, so that the employee count in the last row of the table will be the total number of current employees. The HireDate attribute of the Employee table is an SQL date. Your query may use the year() function which, given an SQL date, will return the year portion of the date. For example, year( 02/26/2005 ) will return the year Do not use any other built-in SQL functions. CS348 8 of 12

9 Question 4. (17 marks) a. (6 marks) Write an SQL query that will report, for each department whose name begins with the letters CS, the DeptNo and the total number of employees who work for that department (i.e., who have that department as their WorkDept). Your query should correctly handle departments that have no employees. CS348 9 of 12

10 b. (6 marks) Consider the following SQL view: create view RespAccountants(EmpNo, ProjNo) as select P.RespEmp, P.ProjNo from Project P, Employee E, Department D where P.RespEmp = E.EmpNo and E.WorkDept = D.DeptNo and D.DeptName = Accounting Can this view be updated? If yes, explain why. If no, give an example of an ambiguous update and explain why it is ambiguous. c. (5 marks) List two reasons why you would define a view such as the one given in part (b) of this question. In the three-schema architecture, which schema do SQL views represent? CS of 12

11 Question 5. (16 marks) Consider the following C function with Embedded SQL: int PrintEmployeePhone1(char employeenum[]) { EXEC SQL BEGIN DECLARE SECTION; char empno[7]; char phonenum[13]; short int phoneind; EXEC SQL END DECLARE SECTION; strcpy(empno, employeenum); EXEC SQL SELECT phoneno INTO :phonenum :phoneind FROM employee WHERE empno = :empno; if (SQLCODE < 0) { return (-1); } /* error */ else if (... more error checking here...) {... }... else { printf("%s\n", phonenum); } return (0); } a. (2 marks) What is the purpose of the host variable phoneind? b. (3 marks) How should this variable be used after the EXEC SQL SELECT statement? You may answer this part of the question by adding some code to the listing above showing how the variable should be used. CS of 12

12 c. (11 marks) Write a variant of the above function that prints the phone numbers of all the employees in a given department (printing nothing for employees who do not have a phone number). The declaration for this function is as follows: int PrintEmployeePhone2(char deptnum[]) Your function should execute the following SQL query to get the required phone numbers: SELECT phoneno FROM employee WHERE deptno = :deptno; Assume that deptno has the same data type and length as empno. CS of 12