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Databases Flashcards

7 cards from real GATE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which normal form eliminates transitive dependencies in a relation?

    Answer: 3NF

    3NF removes transitive dependencies where a non-key attribute depends on another non-key attribute.

  2. In SQL, which isolation level prevents dirty reads but allows non-repeatable reads?

    Answer: READ COMMITTED

    READ COMMITTED ensures a transaction only reads committed data, preventing dirty reads but not non-repeatable reads.

  3. What is the result of a natural join between R(A,B,C) and S(B,C,D)?

    Answer: A relation with attributes A,B,C,D joined on B and C

    Natural join automatically joins on all common attributes (B and C) and produces a result with no duplicate columns.

  4. In the context of B+ trees, what is the minimum number of keys in a non-root node of order m?

    Answer: ⌈m/2⌉ - 1

    A non-root node in a B+ tree of order m must have at least ⌈m/2⌉ - 1 keys to maintain the fill-factor invariant.

  5. Which relational algebra operation is equivalent to the SQL HAVING clause?

    Answer: Selection (σ) applied after aggregation

    HAVING filters groups after aggregation, equivalent to applying selection on the result of a group-by aggregation in relational algebra.

  6. Which of the following is NOT a property of transactions guaranteed by ACID?

    Answer: Distribution

    ACID stands for Atomicity, Consistency, Isolation, and Durability — Distribution is not part of ACID.

  7. A relation R has 3 candidate keys. The minimum number of superkeys R must have is:

    Answer: At least 7

    Every superset of a candidate key is also a superkey, so with 3 candidate keys the count depends on attribute count but is at least 7 (3 keys + their unions).