Learn. Practice. Feel prepared.
DBMS Objective Questions and Answers - Set 2
This DBMS quiz contains carefully curated objective questions with correct answers and clear explanations. It is designed for computer science students, backend developers, and interview preparation, focusing on database design, SQL internals, transactions, indexing, and performance tuning. This is part 2 of the series.
Practice DBMS MCQs with Detailed Explanations
Answer at least 12 questions to submit and verify answers.
16 Which SQL command is DDL? Easy
Correct answer:
CREATE
CREATE defines database structure and belongs to DDL.
17 Which join returns unmatched rows from the left table? Medium
Correct answer:
Left outer join
Left outer join includes all rows from the left table even if no match exists.
18 Which problem is addressed by multiversion concurrency control? High
Correct answer:
Read-write conflicts
MVCC allows readers and writers to operate without blocking by maintaining multiple versions.
19 What is the main disadvantage of bitmap indexes? Medium
Correct answer:
Inefficient for high-cardinality columns
Bitmap indexes perform poorly when the number of distinct values is high.
20 Which SQL clause filters grouped data? Medium
Correct answer:
HAVING
HAVING is applied after grouping to filter aggregate results.
21 Which failure requires redo during recovery? High
Correct answer:
System crash
After a system crash, committed transactions may need redo.
22 Which key uniquely identifies a tuple? Medium
Correct answer:
Candidate key
Candidate keys are minimal keys that uniquely identify tuples.
23 Which join produces maximum number of rows? Medium
Correct answer:
Cross join
Cross join produces Cartesian product of the two relations.
24 Which schedule avoids cascading rollback? High
Correct answer:
Cascadeless
Cascadeless schedules ensure transactions only read committed data.
25 Which index is automatically created with primary key? Medium
Correct answer:
Clustered index
Primary keys usually create clustered indexes by default.
26 Which SQL function returns NULL if input is NULL? Medium
Correct answer:
SUM
SUM returns NULL when all input values are NULL.
27 Which normal form removes multivalued dependency? High
Correct answer:
4NF
Fourth Normal Form removes multivalued dependencies.
28 Which problem occurs when two transactions update same data simultaneously? Medium
Correct answer:
Lost update
Lost update occurs when updates overwrite each other.
29 Which clause is mandatory with GROUP BY? Medium
Correct answer:
Aggregate functions
GROUP BY is meaningful only with aggregate functions.
30 Which optimizer uses statistics to choose execution plans? High
Correct answer:
Cost-based
Cost-based optimizers evaluate multiple plans using statistics.