What this topic covers
11 subtopics- Transactions8
- SQL7
- Indexing6
- Keys6
- Decomposition4
- Relational algebra4
- Functional dependencies3
- Normal forms3
- Concurrency control2
- ER model1
- Recovery1
- Beginner 15
- Intermediate 15
- Advanced 15
About this topic
GATE DBMS questions reward precise reasoning: find every candidate key, decide the highest normal form, check whether a decomposition is lossless, classify a schedule. Here every multiple-select question was checked by a program that tests each option (closures, the chase test, precedence graphs), SQL counts were produced by running the query, and every numerical answer was computed. These are pattern questions written for practice, not previous-year questions.
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Sample questions
Try each one first, then open the answer for the explanation and why the other options are wrong.
Which of these are candidate keys?
R(A, B, C, D, E) with FDs A → B, BC → E, ED → A
Show answer and explanation
Explanation
C and D appear on no right side, so every key contains CD; CD⁺ = CD is not enough. Adding A, B or E each gives all attributes, and each of ACD, BCD, CDE is minimal. ABD lacks C.
How many candidate keys does R have?
R(A, B, C, D, E, F) with FDs AB → C, C → D, D → A, E → F
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
B and E are on no right side, so every key contains BE (BE⁺ = BEF). Adding A, C or D completes it: ABE, BCE, BDE – all minimal.
Which of these are candidate keys?
R(A, B, C, D, E) with FDs AB → C, C → D, D → B, D → E
Show answer and explanation
Explanation
A is on no right side, so every key contains A; A⁺ = A. AB⁺, AC⁺ and AD⁺ all reach ABCDE (C → D → B, E). BC lacks A.