DBMS Questions Answers GATE 2022

Database Management System (DBMS) GATE Question Answers with Explanation.

Q1 – In a relational data model, which one of the following statements is TRUE? (GATE 2022)

A relation with only two attributes is always in BCNF.
If all attributes of a relation are prime attributes, then the relation is in BCNF.
Every relation has at least one non-prime attribute.
BCNF decompositions preserve functional dependencies.

Ans – (1)

Explanation –

Q2 – Consider the following three relations in a relational database.

Employee(eId, Name), Brand(bId, bName), Own(eId, bId)

Which of the following relational algebra expressions return the set of eIds who own all the brands? (GATE 2022)

π_eId ( π_{eId, bId} (Own) / π_bId (Brand))
π_eId(Own) – π_eId(π_Iid (Own) / π_bId (Brand)) – π_{eId, bId} (Own))
π_eId ( π_{eId, bId} (Own) / π_bId (Own))
π_eId ( π_{eId, bId} (Own) x π_bId (Own)/ π_bId (Brand))

Ans – (1, 2)

Explanation –

Q3 – Which of the following statements is/are TRUE with respect to deadlocks? (GATE 2022)

Circular wait is a necessary condition for the formation of deadlock.
In a system where each resource has more than one instance, a cycle in its wait-for graph indicates the presence of a deadlock.
If the current allocation of resources to processes leads the system to unsafe state, then deadlock will necessarily occur.
In the resource-allocation graph of a system, if every edge is an assignment edge, then the system is not in deadlock state.

Ans – (1, 4)

Explanation –

Q4 – Consider a relation R(A, B, C, D, E) with the following three functional dependencies.

𝐴𝐵 → 𝐶; 𝐵𝐶 → 𝐷; 𝐶 → 𝐸;

The number of superkeys in the relation R is _____________. (GATE 2022)

Ans – (8)

Explanation –

Q5 – Let R_i(z) and W_i(z) denote read and write operations on a data element z by a transaction T_i, respectively. Consider the schedule S with four transactions.

S: R₄(x)R₂(x)R₃(x)R₁(y)W₁(y)W₂(x)W₃(y)R₄(y)

Which one of the following serial schedules is conflict equivalent to S? (GATE 2022)

(A) 𝑇₁ → 𝑇₃ → 𝑇₄ → 𝑇₂

(B) 𝑇₁ → 𝑇₄ → 𝑇₃ → 𝑇₂

(C) 𝑇₄ → 𝑇₁→ 𝑇₃ → 𝑇₂

(D) 𝑇₃ → 𝑇₁ → 𝑇₄→ 𝑇₂

Ans – (1)

Explanation –

Q6 – Consider the relational database with the following four schemas and their respective instances.

Student(sNo, sName, dNo) Dept(dNo, dName)

Course(cNo, cName, dNo) Register(sNo, cNo)

SQL Query:

SELECT * FROM Student AS S WHERE NOT EXIST

(SELECT cNo FROM Course WHERE dNo = “D01”

EXCEPT

SELECT cNo FROM Register WHERE sNo = S.sNo)

The number of rows returned by the above SQL query is___________. (GATE 2022)

Ans – (2)

Explanation –