Normalization & Keys

JKSSB Sub-Inspector (Telecommunication) · Database Management Systems · 19 practice questions with answers and explanations: 9 Easy, 10 Medium, 0 Hard.

Sample questions

Sample Easy question 1

Which key is chosen from the candidate keys to identify rows?

  1. Composite key
  2. Foreign key
  3. Super key
  4. Primary key
Show answer

Answer: D. One candidate key is selected as the primary key; the others become alternate keys.

Sample Easy question 2

A candidate key is:

  1. A minimal set of columns that can uniquely identify a row
  2. A key shared by all tables
  3. A key that may contain NULL values freely
  4. Any set of columns in the table
Show answer

Answer: A. A candidate key is a minimal super key.

Sample Easy question 3

If X → Y and Y → Z hold, then X → Z holds. This rule is called:

  1. Augmentation
  2. Reflexivity
  3. Transitivity
  4. Decomposition
Show answer

Answer: C. Armstrong's transitivity rule.

Sample Medium question 4

A relation R(A, B, C) has A as its only candidate key. How many super keys does it have?

  1. 4
  2. 6
  3. 8
  4. 3
Show answer

Answer: A. Every super key must contain A: {A}, {A,B}, {A,C} and {A,B,C}.

Sample Medium question 5

Which anomaly occurs when deleting a row accidentally removes other useful facts?

  1. Update anomaly
  2. Selection anomaly
  3. Insertion anomaly
  4. Deletion anomaly
Show answer

Answer: D. Redundant, unnormalised tables can lose facts when a row is deleted.

Sample Medium question 6

In R(A, B, C, D) the dependencies are A → B, B → C and C → D. What is the candidate key?

  1. B
  2. A
  3. C
  4. D
Show answer

Answer: B. A+ = {A, B, C, D}, and no other single attribute determines A.

More Database Management Systems topics for JKSSB Sub-Inspector (Telecommunication)

Related articles