Classical

Database MCQ - ER-model & Relational Model

61:  

Why do we have to create a primary index on a primary key 

A.

Ease of searching

B.

Sequential ordering of a file

C.

Both (a) and (b)

D.

None of these

 
 

Option: C

Explanation :


62:  

In context with relational Algebra. Which of the following are unary operatiors.
1.Select
2. Project
3. Union
4. Product

A.

1 and 3 only

B.

2 and 4 only

C.

1 and 2 only

D.

All are binary

 
 

Option: C

Explanation :


63:  

Let R is a relation schema, R(A, B, C, D) and F = {A —> B, B --> C, C —> A) is the set of functional dependency. Determine the key of relation ?

A.

A

B.

B

C.

C

D.

D

 
 

Option: D

Explanation :

Rule to find out the key in relation :-

  • Key ---> Rest of Attributes
    1. As Key determies rest of the attributes 
    2. Key must include all attributes but can not be on RHS of any functional dependency i.e Only fields on RHS are determined. 
    3. An undetermined field must be in the key.
    4.  REST must include all attributes but  NOT on LHS  They don't determine anything  so they can not be part of key.
    5. If field is not in ANY FD, it must be part of the key

Now considering these 5 points we get D as Key.


64:  

Which of the following statement is correct?

A.

F |= x ---> x  iff y ⊆ x+

B.

F |= y ---->x iff y ⊆ x+

C.

F |=x  --->y iff  x+ ⊆ y

D.

F |= y --->x iff x+⊆ y

 
 

Option: A

Explanation :


65:  

Given the basic ER and relational model which of the following is incorrect?

A.

 An entity can have more than one attrbute

B.

An attribute of an entity can be composite.

C.

In row of a relational table, an attribute have more than one value.

D.

In row of a relational table, an attribute can have exactly one vlaue or a  NULL value.

 
 

Option: C

Explanation :




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