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华南农业大学期末考试试卷（A卷）
2014-2015学年第一学期 考试科目： 数据库系统 考试类型：闭卷 考试时间： 120 分钟 学号 姓名 年级专业
装题号 得分 评阅人 一 二 三 四 五 六 总分 订线
Question 1: true-false question (15 points) For each of the following statements, indicate whether it is TRUE or FALSE (Using √ for TRUE and × for FALSE). You will get 1 point for each correct answer, -0.5 point for each incorrect answer, and 0 point for each answer left blank. Be sure to write your answer in the answer sheet.
1. A primary key is a field (or group of fields) that uniquely describes each record in
the database.
2. Data redundancy improves the integrity of a database.
3. SQL is the language used by relational databases to create objects and to
manipulate and retrieve data.
4. A relational database management system does not include tools for backing up &
restoring databases.
5. An attribute is also known as a row in most databases. 6. An association between entities is known as a relationship.
7. Integrity constraints limit the number of entities that can be placed in a table or
database.
8. The Entity-Relationship data model is often used in the physical design phase. 9. The concept “relation” in relation model is exactly the same as the concept
“relationship” in ER model.
10. Most relationship sets in a database system involves two entity sets. 11. The closure of an attribute set contains that attribute set.
12. Lossless decomposition is necessary in a decomposition algorithm. 13. If A → B and C → D hold, then AC → BD also holds.
14. It is not necessary that a legal schedule preserves the order in which the
instructions appear in each individual transaction.
15. Update operations in database must be written into log before updating database.
Question 2 single-choice question (2 points for each problem, 30 points in total) 1. is the only one incorrect description from the followings: A. R=(R-S)∪(R∩S) B. R-S=R-(R∩S) C. R∩S=S-(R-S) D. R∩S=S-(S-R)
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2. Choose the only one correct expression from the followings: _ ______.
A. (? some) ? in B. (= all) ? not in C. exists r ? r ? ? D. X-Y ?? ? X ? Y 3. of the following four expressions of relational algebra is not equivalent to the other three? They are all based on the relations R(A,B) and S(B,C).
A.?A,B?R??S? B. R???B?S? C.
?A,R.B?R?S? D.R???A?R???B?S??
4. In the following, assume a is an attribute of some character-string type, e.g. CHAR(10), and that it may be NULL.
Q1: SELECT * FROM R WHERE a IS NULL;
Q2: SELECT * FROM R WHERE a NOT LIKE '%'; A.Q1 and Q2 produce the same answer.
B. The answer to Q1 is always contained in the answer to Q2. C. The answer to Q2 is always contained in the answer to Q1. D. Q1 and Q2 produce different answers.
5. The Entity-Relationship data model is A. DBMS dependent B. DBMS independent C. both A and B D. neither A nor B 6. In SQL, an UPDATE statement without a WHERE clause: A. Updates every row in a table. B. Updates no rows in a table. C. Updates every column in a table. D. Results in a Cartesian product.
7. If a course can be taught by many teachers, and a teacher can teach only one course, then the mapping cardinality from course to teacher is
A. one-to-one B. one-to-many C. many-to-one D. many-to-many
8. If there is a many-to-one relationship between entity A and B, then A. there exists a functional dependency from the primary key in B to the primary key in A, i.e., PK(B) → PK(A).
B. there exists a functional dependency from the primary key in A to the primary key in B, i.e., PK(A) → PK(B). C. both A and B. D. neither A nor B
9. If a functional dependency AB→R holds on relation R(A, B, C), then (A, B) is definitely a ______ of R.
A. super key B. primary key C. candidate key D. foreign key
10. A relational schema R is in _____ if the domains of all attributes of R are atomic
A. 1NF B. 3NF C. BCNF D. 4NF 11. Which one of the following statement is true?
A. 3NF is more strict than BCNF B. 4NF is more strict than BCNF
C. 1NF is more strict than BCNF D. BCNF is the most strict normal form 12. If a transaction Ti has obtain an exclusive lock on data item Q, then transition Tj can ______.
A. obtain an exclusive lock on data item Q B. obtain a shared lock on data item Q C. wait for lock granting on data item Q D. read or write Q without a lock
13. If both
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14. ______ is the final state in a life cycle of a transaction. A. committed B. aborted C. failed D. A or B
15. in 2PL protocol, at stage, A transaction may obtain locks, but may not release locks.
A. Shrinking phase B. Growing phase C. Committed D. Aborted
Question 3 (12 points) Consider the following database requirement:
A hospital has properties like ID, name, location, rank, capacity. A doctor can be described by ID, name, age, skill. A patient has properties like ID, name, age, sex, address. The above three entities must satisfy some constraints: Each doctor can be unemployed or employed by one hospital. If a doctor is employed, his salary needs to be recorded in the database. A patient can go to many hospitals.
1. Draw ER diagram to illustrate the above database requirement [8 points].
2. Translate your ER diagram into relational database schemas, and point out the primary keys and foreign keys. You can write your answers in the following format: “R(a1, a2, a3, a4), primary key: a1, foreign key: a4” [4 points].
Question 4. (24 points) The following five tables are for a company management system:
EMPLOYEE (ID, Name, Birthday, Address, Sex, Salary, Dnumber) DEPARTMENT (Dnumber, Dname, MgrID ) PROJECT (Pnumber, Pname, Pcity)
WORKS_ON (Pnumber, E-ID, Wdate, Hours)
CHILD (E-ID, CHD-ID, CHD_name, Sex, Birthday)
1. Based on the giving relations, Specify the following queries using relational algebra (3 points for each).
1) List the names of all employees with birthday earlier than ‘1970-1-1’ and salary less than $5000.
2) List the names of all employees who have a child.
3) List the cities and the total number of projects which are located on same city.
2. Specify the following operations in SQL(3 points for each).
1) Define the table WORKS_ON, declare Pnumber, E-ID, Wdate as the primary key, Pnumber as the foreign key referencing the primary key of project, E-ID as the foreign key referencing the primary key of employee, and ensure that the values of Hours are non-negative with default value 8.
2) For each employee working on the ‘Network’ project (Pname), increase his/her salary by 5%.
3) List the names of all department managers who have no child.
4) Find the names of all employees in department 5 (Dnumber) who have worked on both 'X' project and 'Y' project (Pname).
5) For each project, find the project number, project name and the total hours (by all employees) spent on that project in Oct. 2009.
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