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DBI202 Exam |Questions with 100% Correct Answers
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DBI202 Exam |Questions with 100% Correct Answers
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DBI202 Exam |Questions with 100%Correct Answers
Relation R(x,y) currently consists of only one tuple (NULL, NULL). Which of the following
queries will produce a nonempty output? That is, at least one tuple will be produced, although
the tuple(s) may have NULL's. - ✔ ✔ SELECT * FROM R WHERE x IS NULL
What operator tests column for the absence of data? - ✔ ✔ IS NULL operator
Choose one correct statement: Two null values are equal Comparisons between two null values, or
between a NULL and any other value, return unknown Comparisons between two null values, or
between a NULL and any other value, return FALSE - ✔ ✔ ----and any other value,
return unknown
A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable).
What does "Durable" mean? - ✔ ✔ "Durable" means that: Transactions that have committed
will survive permanently
A database transaction, by definition, must be ACID (atomic, consistent, isolated and durable).
What does "Isolated" mean? - ✔ ✔ "Isolated" means that: how/when the changes made by
one operation in one transaction become visible to other concurrent operations in other
transactions
Choose the in-correct statement: In SQL Server, every DML operation is a transaction regardless of
whether it has a BEGIN TRANSACTION or not COMMITTING a transaction makes permanent
,the changes resulting from all SQL statements in the transaction ROLLING back a transaction
rejects any of the changes resulting from the SQL statements in the transaction When the
sequence of tasks is complete, the SAVE POINT closes the transaction - ✔ ✔ When the
sequence of tasks is complete, the SAVE POINT closes the transaction
In order to modify or delete an existing constraint, it is necessary that: - ✔ ✔ the constraint has
a name
x <= 100 AND NOT(y >= 15 OR z = 35) have the truth value UNKNOWN? - ✔ ✔ x = NULL, y = 0, z
= 4.
The IN SQL keyword - ✔ ✔ Determines if a value
A ____ is a logically coherent collection of data with some inherent meaning, representing
some aspect of real world and being designed, built and populated with data for a
specific purpose - ✔ ✔ Database
Which of following is never used as a data model? - ✔ ✔ None of the others
A ___ is a notation for describing the structure of the data in a database, along with
the constraints on that data - ✔ ✔ data model
Which statement is used to remove a relation named R - ✔ ✔ DROP TABLE R
Given a relation R(A,B,C,D). Which of the followings is trivial? - ✔ ✔ A-->BCD
Let R(ABCD) be a relation with functional dependencies {A -> B, C -> B, B -> D}What is the key
for R (choose one) - ✔ ✔ AC
, The relation R(ABCD) has following FDs:{ A -> B ; B -> A ; A -> D ; D -> B } - ✔ ✔ R is in 3NF
What is the difference between the 2NF and the 3NF? - ✔ ✔ 2NF deals with partial
functional dependency, while 3NF deals with transitive functional dependency
The key for a weak entity set E is - ✔ ✔ Zero or more attributes of E and key attributes
from supporting entity sets
A class in UML is similar to - ✔ ✔ An entity set in E/R model
An association class in UML is similar to ______ in the ER model - ✔ ✔ attributes on a
relationship
Which of the following is NOT a standard aggregation operator? - ✔ ✔ group
T intersect(R union S) = (T intersect R) union (T intersect S)The above law still hold for
bag relations? - ✔ ✔ false
Choose the correct statement: Aggregate functions perform a calculation on a set of values
and return a single value. Aggregate functions perform a calculation on a single value and
return a single value - ✔ ✔ Aggregate functions perform a calculation on a set of values and
return a single value
SELECT SUM(D) FROM S WHERE D < 8 AND D > 5:a 4 6, c 6 8, c 5 5, e 9 9, F 10 10,c 7 9 - ✔ ✔ 6
(1,2), (1,2), (2,3), (3,4), (3,4), (4,1), (4,1), (4,1), (4,2) : SELECT a1.x, a2.y, COUNT(*) FROM Arc
a1, Arc a2 WHERE a1.y = a2.x GROUP BY a1.x, a2.y; - ✔ ✔ (3,1,2)
A B : 10 x, 30 y, 50 z, 70t, B C D:x 40 60,z 60 80,z 50 50,z 70 90 - ✔ ✔ (30,y) (70,t)
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