Database Management Systems Mcqs

Page No. 6

SELECT name FROM instructor WHERE salary IS NOT NULL; Selects


aTuples with null value


bTuples with no null values


cTuples with any salary


dAll of the mentioned



The predicate in a where clause can involve Boolean operations such as and. The result of true and unknown is_______ false and unknown is _____ while unknown and unknown is _____


aUnknown, unknown, false


bTrue, false, unknown


cTrue, unknown, unknown


dUnknown, false, unknown



If the attribute phone number is included in the relation all the values need not be entered into the phone number column. This type of entry is given as


a0


b


cNull


dEmpty space


View Answer Null

A _____ indicates an absent value that may exist but be unknown or that may not exist at all.


aEmpty tuple


bEmpty tuple


cNull value


dOld value


View Answer Null value

We can test for the nonexistence of tuples in a subquery by using the _____ construct.


aNot exist


bNot exists


cExists


dExist


View Answer Not exists

The phrase “greater than at least one” is represented in SQL by _____


a< all


b< some


c> all


d> some


View Answer > some

The ____ connective tests for set membership, where the set is a collection of values produced by a select clause. The ____ connective tests for the absence of set membership.


aOr, in


bNot in, in


cIn, not in


dIn, or


View Answer In, not in

A Boolean data type that can take values true, false, and________


a1


b0


cNull


dUnknown


View Answer Unknown

All aggregate functions except _____ ignore null values in their input collection.


aCount(attribute)


bCount(*)


cAvg


dSum


View Answer Count(*)

SELECT COUNT (____ ID) FROM teaches WHERE semester = ’Spring’ AND YEAR = 2010;
If we do want to eliminate duplicates, we use the keyword ______in the aggregate expression.


aDistinct


bCount


cAvg


dPrimary key


View Answer Distinct

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