CS40 Exam #2 November 13, 2002

Transcription

1 CS40 Exam #2 November 13, 2002 Name: Except where explicitly noted, all of the questions on this exam refer to the database defined by the relational schemas given on the last page of this exam. 1. For the following questions, make no assumptions about the database, other than what is given in the schema definition. Do assume that the database management system strictly enforces referential integrity. a. Write the SQL necessary to insert the new 4-credit CS course CS38, entitled 3D Animation and Virtual Reality, which has CS22 and CS34 as prerequisites. (You may assume that CS22 and CS34 are already in the database.) [6 points] b. Every CS95 course must become a regular catalog course after it has been taught three times. Since this is true of the CS95 course Web-Based Application Design, suppose it has been approved and renumbered CS39. Write the SQL necessary to implement this change. (Keeping in mind that the students who previously took the course must have the new number reflected.) [7 points] c. Suppose CS32 is to be dropped from the catalog. Write the SQL necessary to delete it from the Course table. Assume that its prerequisite information is also to be deleted, but the record of sections of CS32 that were taught is to be maintained. [7 points]

2 2. a. Give the SQL statements necessary to create the Course, Prereq and Sections tables. Make sure that all of the schema details are accounted for, and assume that the tasks described in the first question can be generalized. (For example, whenever a course is deleted, its prerequisite information is also to be deleted but information about its sections is to be maintained.) [12 points] b. Show how these changes would simplify your answers to question 1 (if at all). [8 points]

3 3. Write SQL queries for the following: [10 points each] a. List the name and class year of all freshmen and sophomores who have made a B or better in a CS course, ordered alphabetically. b. List the student number and name of students who have not received a grade in a course taught by either Professor Gabbert or Professor Catron. Don t repeat names. 4. Write SQL queries for the following: [10 points each] a. List the year, department, and total number of students for the year for all CS and English courses, ordered alphabetically by department and within department by year. The column headers should be appropriately labeled. b. List the section ID, course name, instructor and count of students for sections that had 5 or fewer students who received a grade.

4 5. Indicate whether or not the statement is true or false. If it is false, correct the statement and give an explanation. Do not simply negate the statement. (For example, don t simply replace is with is not.) [2 points each] a. In Java, the class.forname method is used to both create an instance of a Driver and register the Driver with the DriverManager. b. All of the database management systems that we have studied enforce the concept of referential integrity. c. Macros are used in Microsoft Access to process SQL queries. d. The default setting for any foreign key in Oracle is ON DELETE RESTRICT. e. Code for the DriverManager and Driver classes in Java are provided by specific vendors (Oracle, MySQL, etc.) as part of a JDBC package. f. The PHP mysql_db_query function can be used to execute SELECT, UPDATE and DELETE statements. g. Large binary files (like MP3s, images and Word files) cannot be stored in the fields of a database, because no SQL data type exists for them. h. In the student database schema, stuname is not an atomic attribute. Consequently, it is impossible to identify student records by last name only. i. A left join operation on two tables produces the same result as a regular join. j. Query plan is another term for a relational algebra expression that implements a SQL statement.

5 6. Short Answer: [5 points each] a. Cite and explain one specific reason why it is desirable to write a database application, other than a prettier interface. Give an example. b. Give two relational algebra expressions that could be used to implement the following SQL statement, and discuss which of the two should be chosen by the query processor. SELECT s.cournum,g.grade FROM Sections s, Grades g WHERE s.secid=g.secid AND s.cournum= CS40 AND g.grade= A ; c. Describe the most important difference between the use of CGI and Java servlets to implement online databases. d. Give a SQL statement to create a view named StudentGrades that contains the fields: stunum, stuname, secid, and grade, in order of increasing secid. Then give a short statement that would retrieve information from the view for stunum=42.

6 Relational Schemas for Course and Grade Database Table Attribute Data Type Keys and custom rules Student stunum number(4) primary key, stunum is between 8 and 20 stuname varchar2(20) must have a value class number(1) class is 1, 2, 3 or 4 major varchar2(4) Course cournum varchar2(6) primary key courname varchar2(30) must have a value credithr number(1) credithr is 2 or 4, defaults to 4 dept varchar2(4) Prereq cournum varchar2(6) primary key and foreign key prereqnm varchar2(6) primary key and foreign key Cournum and prereqnm together form the primary key. Separately they are foreign keys. Sections secid number(4) primary key cournum varchar2 (6) foreign key, defaults to XXXXX semester varchar2(6) must have a value acadyear number(4) year is between 1998 and 2002 instr varchar2(10) must have a value Grades stunum number(4) part of primary key and a foreign key secid number(4) part of primary key and a foreign key Stunum and secid together form the primary key. Separately they are foreign keys. grade char 1 grade is A, B, C, D, or F