Đề thi trắc nghiệm cơ sở dữ liệu trường Cao Thắng - phần 4 docx

The ____ set operator will show all rows common to both tables A and B.. Using the product operator, if table A has 2 rows and table B has 4 rows, the number of rows in the product of th

10 The set operator will show all rows common to both tables A and B

(a) intersection

(b) union

(c) difference

(d) product

11 Using the product operator, if table A has 2 rows and table B has 4 rows, the number of

rows in the product of these two tables is:

(a) 4

(b) 8

(c) 16

(d) 20

12 Suppose relation R(A,B,C,D,E) has the following functional dependencies:

A → B

B → C

BC → A

A → D

D → E

Which of the following is not a key?

(a) A

(b) E

(c) B

(d) D

(e) (b) and (d)

13 Consider a relation Q with five attributes L V O B Y You are given the follwoing

dependencies: L → V; VO → Y and YB → L

The number of superkeys of Q is: (not superkeys)

(a).2

(b).3

(c),4

(d).5

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Biên soạn : Phan Tấn Quốc- Trường Cao Đẳng Kỹ Thuật Cao Thắng

14 Use the following tables and data,All of the fields are

Integers.The table names are Q

A B C D

1 2 3 4

1 3 5 7

2 3 4 5

2 4 6 8

5 6 7 8

How many records does the following SQL example return?

SELECT * FROM Q WHERE A>=5 OR D>=7;

a) 1

b) 2

c) 3

d) 4

15 How many records does the following SQL example return?

SELECT sum(A) AS S FROM Q GROUP BY A;

16 The SQL below will return one value What is it?

17 How many records does the following SQL example return?

SELECT count(*) FROM Q GROUP BY A, B;

a) 2

b) 3

c) 4

d) 6

e) None of the above

18 Use the following tables and data All of the fields are Integers.The table names are R and

How many records does the following SQL example return? SELECT COUNT(*) FROM R, S WHERE R.A=S.D OR R.B=S.E;

a) 1

b) 2

c) 3

d) 4

19 How many records does the following SQL example return? SELECT COUNT(*) FROM R, S WHERE R.A=S.D;

a) 0

b) 1

c) 2

d) 4