ER Model & Relational Algebra
JKSSB Sub-Inspector (Telecommunication) · Database Management Systems · 18 practice questions with answers and explanations: 10 Easy, 8 Medium, 0 Hard.
Sample questions
Sample Easy question 1
What does the cardinality of a relation mean?
- The number of relationships
- The number of tuples (rows)
- The number of attributes
- The number of foreign keys
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Answer: B. Cardinality counts the tuples in a relation.
Sample Easy question 2
In relational algebra, which symbol denotes selection?
- ⋈ (join)
- σ (sigma)
- π (pi)
- ∪ (union)
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Answer: B. σ selects rows that satisfy a condition.
Sample Easy question 3
In relational algebra, which operator picks specific columns?
- − (difference)
- π (projection)
- × (Cartesian product)
- σ (selection)
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Answer: B. π projects chosen attributes and removes duplicates.
Sample Medium question 4
A relationship in which one department has many employees but each employee belongs to one department is:
- One-to-one (1:1)
- Zero-to-zero
- Many-to-many (M:N)
- One-to-many (1:N)
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Answer: D. One department maps to many employees.
Sample Medium question 5
How is a many-to-many relationship usually implemented in a relational database?
- With a separate junction (linking) table
- With a single column
- By merging both tables
- It cannot be implemented
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Answer: A. The junction table holds the foreign keys of both entities.
Sample Medium question 6
What is a weak entity?
- An entity that has no key of its own and depends on a strong entity
- An entity that holds no data
- An entity with no attributes
- An entity with alone one row
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Answer: A. A weak entity is identified by its owner entity together with a partial key.