DBI202 02

QN=21 (8032) An association class in UML is similar to ______ in the ER model

• a. attributes on a relationship

• b. Attributes

• c. Entities

• d. entity sets

QN=22 (8009) In UML, what is the difference between an aggregation and a composition?

• a. In composition, when the owning object is destroyed, so are the contained objects. In aggregation, this is not necessarily true.

• b. In aggregation, when the owning object is destroyed, so are the contained objects. In composition, this is not necessarily true.

• c. All of the others

• d. There is no difference between an aggregation and a composition

QN=23 (8222) Which of the following is NOT a standard aggregation operator?

• a. GROUP

• b. SUM

• c. COUNT

• d. AVG

QN=24 (8238) Consider the law, that holds for set relations:
T intersect(R union S) = (T intersect R) union (T intersect S) The above law still hold for bag relations?

• a. True

• b. False

QN=25 (8236) Choose the correct statement:

• a. Aggregate functions perform a calculation on a set of values and return a single value

• b. Aggregate functions perform a calculation on a single value and return a single value

• c. Aggregate functions perform a calculation on a set of values and return a relation

• d. Aggregate functions perform a calculation on a set of values and return a row

QN=26 (8507) Suppose the relation S(B,C,D) has tuples:

B C D
------------------------------------
a 4 6
c 6 8
c 5 5
e 9 9
F 10 10
c 7 9

Compute the result of the following query:

SELECT SUM(D)
FROM S
WHERE D < 8 AND D > 5

Choose the row that appears in the computed result.

• a. 6

• b. 7

• c. 8

• d. 9

QN=27 (8500) Suppose the relation S(B,C,D) has tuples:

B C D
-----------------------------------
a 4 6
c 6 8
c 5 5
e 9 9
f 10 10
c 7 9

Compute the result of the following query:

SELECT D, SUM(C)
FROM S
GROUP BY D

Choose rows that are appear in the computed result

• a. (9,12)

• b. (9,14)

• c. (9,16)

• d. (9,18)

QN=28 (8509) Column A of a relation has the following list of values in the six rows of the table:

NULL, NULL, 10, 10, 20, 30

In SQL Server, which of the following is the correct value of
AVG(DISTINCT A)?

• a. 15

• b. NULL

• c. 20

• d. 10

QN=29 (8513) The table Arc(x,y) currently has the following tuples (note that there are duplicates): (1,2), (1,2), (2,3), (3,4), (3,4), (4,1), (4,1), (4,1), (4,2). Compute the result of the query:

SELECT a1.x, a2.y, COUNT(*)
FROM Arc a1, Arc a2
WHERE a1.y = a2.x
GROUP BY a1.x, a2.y;

Which of the following tuples is in the result?

• a. (3,1,2)

• b. (1,3,4)

• c. (2,4,6)

• d. (3,2,6)

QN=30 (8517) How we can understand about this statement:
"All aggregate functions are deterministic"?

• a. This means aggregate functions return the same value any time they are called by using a specific set of input values

• b. This means aggregate functions return the different values each time they are called by using a specific set of input values

• c. This means aggregate functions return the same value any time they are called by using any set of input values

• d. None of the others