DBMS MCQs with Answers and Explanations

Question #61

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In SQL, which operator is used to combine two conditions and returns true if both are true?

A. NOT

B. XOR

C. OR

D. AND

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Correct Answer: Option D

Explanation:
The AND operator returns true only if both conditions are true.

This question belongs to: Computer Database Management System (DBMS)

Question #62

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What is the purpose of the SQL DISTINCT keyword?

A. To sort the result set

B. To filter rows based on a condition

C. To group the results

D. To return only unique rows in the result set

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Correct Answer: Option D

Explanation:
DISTINCT removes duplicate rows from the query result.

This question belongs to: Computer Database Management System (DBMS)

Question #63

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Which of the following is a property of a transaction that ensures that the database remains in a valid state before and after the transaction?

A. Atomicity

B. Consistency

C. Isolation

D. Durability

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Correct Answer: Option B

Explanation:
Consistency ensures that a transaction brings the database from one valid state to another, maintaining all defined rules and constraints.

This question belongs to: Computer Database Management System (DBMS)

Question #64

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What is the main advantage of using a DBMS over a file system?

A. Data security and access control are provided

B. Data consistency is maintained

C. All of the above

D. Data redundancy is minimized

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Correct Answer: Option C

Explanation:
A DBMS offers advantages like reduced redundancy, consistency, security, concurrent access, and backup/recovery compared to file systems.

This question belongs to: Computer Database Management System (DBMS)

Question #65

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Which normal form addresses partial dependencies, i.e., non-prime attributes dependent on part of a composite primary key?

A. BCNF

B. 3NF

C. 1NF

D. 2NF

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Correct Answer: Option D

Explanation:
Second Normal Form (2NF) eliminates partial dependencies by ensuring all non-key attributes are fully functionally dependent on the entire primary key.

This question belongs to: Computer Database Management System (DBMS)

Question #66

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What is a composite key in a database?

A. A key that is made up of multiple columns

B. A key that is always a foreign key

C. A key that references another table

D. A key that is a single column

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Correct Answer: Option A

Explanation:
A composite key is a primary key that consists of two or more columns to uniquely identify a row.

This question belongs to: Computer Database Management System (DBMS)

Question #67

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Which SQL function returns the current date and time?

A. CURDATE()

B. GETDATE()

C. NOW()

D. All of the above depending on the DBMS

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Correct Answer: Option D

Explanation:
Different DBMSs have different functions: MySQL NOW(), SQL Server GETDATE(), etc. But all return current date/time.

This question belongs to: Computer Database Management System (DBMS)

Question #68

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In SQL, what is the purpose of the LIKE operator?

A. To perform pattern matching on strings

B. To join tables

C. To aggregate data

D. To perform arithmetic operations

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Correct Answer: Option A

Explanation:
LIKE is used with wildcards (% and _) to search for a specified pattern in a column.

This question belongs to: Computer Database Management System (DBMS)

Question #69

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Which SQL keyword is used to give users permission to access database objects?

A. PERMIT

B. ASSIGN

C. REVOKE

D. GRANT

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Correct Answer: Option D

Explanation:
GRANT is a DCL command used to assign privileges to users.

This question belongs to: Computer Database Management System (DBMS)

Question #70

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What is the purpose of the REVOKE command in SQL?

A. To rollback a transaction

B. To remove user permissions

C. To delete a table

D. To create a user

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Correct Answer: Option B

Explanation:
REVOKE is used to take away privileges previously granted to users.

This question belongs to: Computer Database Management System (DBMS)

Question #71

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Which type of join returns all rows from the left table and matching rows from the right table?

A. INNER JOIN

B. LEFT JOIN

C. RIGHT JOIN

D. FULL JOIN

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Correct Answer: Option B

Explanation:
LEFT JOIN (or LEFT OUTER JOIN) returns all rows from the left table, with matching rows from the right table; NULLs appear when no match.

This question belongs to: Computer Database Management System (DBMS)

Question #72

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What is a self join?

A. Joining more than two tables

B. Joining two different tables

C. Joining tables without a common column

D. Joining a table with itself

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Correct Answer: Option D

Explanation:
A self join is a join where a table is joined with itself, often used to compare rows within the same table.

This question belongs to: Computer Database Management System (DBMS)

Question #73

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Which SQL function is used to find the maximum value in a column?

A. MIN()

B. SUM()

C. AVG()

D. MAX()

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Correct Answer: Option D

Explanation:
MAX() returns the highest value in a selected column.

This question belongs to: Computer Database Management System (DBMS)

Question #74

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What is the difference between DELETE and TRUNCATE commands?

A. DELETE removes all rows; TRUNCATE removes structure

B. No difference

C. TRUNCATE can have WHERE; DELETE cannot

D. DELETE can be rolled back; TRUNCATE cannot (in most DBMS)

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Correct Answer: Option D

Explanation:
DELETE is a DML command that can be rolled back and can use WHERE; TRUNCATE is a DDL command that removes all rows and cannot be rolled back (in some DBMS) and resets auto-increment counters.

This question belongs to: Computer Database Management System (DBMS)

Question #75

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Which constraint ensures that a column cannot have NULL values?

A. NOT NULL

B. UNIQUE

C. FOREIGN KEY

D. PRIMARY KEY

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Correct Answer: Option A

Explanation:
NOT NULL constraint enforces that a column must have a value, preventing NULL entries.

This question belongs to: Computer Database Management System (DBMS)

Question #76

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Which constraint ensures that all values in a column are unique?

A. UNIQUE

B. PRIMARY KEY

C. FOREIGN KEY

D. CHECK

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Correct Answer: Option A

Explanation:
UNIQUE constraint ensures that all values in a column are distinct, but allows NULL (unless combined with NOT NULL).

This question belongs to: Computer Database Management System (DBMS)

Question #77

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What is a super key in a relational database?

A. A set of attributes that uniquely identifies a row

B. Both A and B

C. A key that has extra attributes beyond a candidate key

D. A key that includes the primary key

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Correct Answer: Option B

Explanation:
A super key is a set of one or more attributes that uniquely identifies a row. A candidate key is a minimal super key.

This question belongs to: Computer Database Management System (DBMS)

Question #78

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Which normal form requires that every determinant is a candidate key?

A. 3NF

B. 2NF

C. 1NF

D. BCNF

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Correct Answer: Option D

Explanation:
Boyce-Codd Normal Form (BCNF) is a stricter version of 3NF where every determinant must be a candidate key.

This question belongs to: Computer Database Management System (DBMS)

Question #79

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In SQL, which statement is used to create a new database?

A. NEW DATABASE

B. CREATE TABLE

C. CREATE SCHEMA

D. CREATE DATABASE

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Correct Answer: Option D

Explanation:
CREATE DATABASE is used to create a new database in SQL.

This question belongs to: Computer Database Management System (DBMS)

Question #80

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What is a relation in relational database terms?

A. A table

B. A column

C. A key

D. A row

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Correct Answer: Option A

Explanation:
In the relational model, a relation is a table consisting of rows and columns.

This question belongs to: Computer Database Management System (DBMS)

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