DBMS MCQs with Answers and Explanations

Question #41

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What is a foreign key in a database table?

A. A column that references the primary key of another table

B. A key used to uniquely identify records in the same table

C. A key that is always indexed

D. A key that allows null values

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Correct Answer: Option A

Explanation:
A foreign key is a field in one table that links to the primary key of another table, establishing a relationship between tables.

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

Question #42

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Which type of relationship is represented by a foreign key in a relational database?

A. Many-to-many

B. One-to-one

C. All of the above

D. One-to-many

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Correct Answer: Option C

Explanation:
Foreign keys can represent various relationships, including one-to-one, one-to-many, and many-to-many (via junction tables).

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

Question #43

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What is the purpose of the SQL 'JOIN' clause?

A. To combine columns from multiple tables into a single table

B. To delete records from a table

C. To create a new table

D. To combine rows from two or more tables based on a related column

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Correct Answer: Option D

Explanation:
JOIN is used to combine rows from different tables based on a common column, allowing querying across related tables.

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

Question #44

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Which SQL keyword is used to remove a table from the database?

A. TRUNCATE

B. DELETE

C. REMOVE

D. DROP

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Correct Answer: Option D

Explanation:
DROP TABLE is a DDL command that deletes the table and its structure from the database.

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

Question #45

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What does the SQL command 'INSERT INTO' do?

A. Adds a new row to a table

B. Deletes rows

C. Creates a table

D. Updates existing rows

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Correct Answer: Option A

Explanation:
INSERT INTO is used to insert new records (rows) into a table.

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

Question #46

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What is normalization in database design?

A. The process of increasing data duplication

B. The process of encrypting data

C. The process of indexing tables

D. The process of organizing data to reduce redundancy and improve integrity

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Correct Answer: Option D

Explanation:
Normalization is the process of structuring a relational database to reduce data redundancy and dependency, typically by dividing large tables into smaller, related tables.

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

Question #47

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Which normal form eliminates all transitive dependencies?

A. BCNF

B. 2NF

C. 1NF

D. 3NF

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Correct Answer: Option D

Explanation:
Third Normal Form (3NF) eliminates transitive dependencies, where non-key attributes depend on other non-key attributes.

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

Question #48

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In SQL, which clause is used to filter rows before grouping?

A. WHERE

B. HAVING

C. ORDER BY

D. GROUP BY

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Correct Answer: Option A

Explanation:
WHERE is used to filter individual rows before aggregation and grouping.

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

Question #49

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Which SQL clause is used to filter groups after grouping?

A. ORDER BY

B. GROUP BY

C. WHERE

D. HAVING

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Correct Answer: Option D

Explanation:
HAVING is used to filter groups based on aggregate conditions, applied after GROUP BY.

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

Question #50

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What is the purpose of the SQL 'GROUP BY' clause?

A. To group rows that have the same values in specified columns into summary rows

B. To filter rows

C. To sort the result set

D. To join tables

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Correct Answer: Option A

Explanation:
GROUP BY organizes data into groups based on the values of one or more columns, often used with aggregate functions.

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

Question #51

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Which aggregate function is used to count the number of rows in a table?

A. SUM

B. AVG

C. MAX

D. COUNT

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Correct Answer: Option D

Explanation:
COUNT returns the number of rows in a table or group.

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

Question #52

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What is the result of the SQL query: SELECT * FROM employees;?

A. An empty result

B. Only the first row

C. All rows and all columns from the employees table

D. Only the primary key column

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Correct Answer: Option C

Explanation:
SELECT * retrieves all columns and rows from the specified table.

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

Question #53

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What is a candidate key?

A. A column that allows duplicate values

B. A set of columns that uniquely identifies a row and can serve as a primary key

C. A foreign key

D. A column that can be used as a primary key but is not chosen

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Correct Answer: Option B

Explanation:
A candidate key is an attribute or set of attributes that can uniquely identify a tuple; one is selected as the primary key.

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

Question #54

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What is an alternate key?

A. A candidate key that is not chosen as the primary key

B. A super key with extra attributes

C. The primary key

D. A foreign key

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Correct Answer: Option A

Explanation:
An alternate key is any candidate key that is not the primary key.

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

Question #55

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Which type of database model organizes data in a tree-like structure?

A. Network model

B. Object-oriented model

C. Hierarchical model

D. Relational model

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Correct Answer: Option C

Explanation:
The hierarchical model arranges data in a parent-child relationship, forming a tree structure.

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

Question #56

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What is the difference between a DBMS and an RDBMS?

A. DBMS supports only flat files; RDBMS supports relational tables

B. DBMS does not support relationships; RDBMS does

C. There is no difference

D. DBMS is a subset of RDBMS

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Correct Answer: Option B

Explanation:
RDBMS is a type of DBMS that organizes data in tables with relationships, enforcing referential integrity using primary and foreign keys, while a DBMS may not support such relationships.

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

Question #57

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Which SQL command is used to modify the structure of an existing table?

A. MODIFY

B. CHANGE

C. ALTER

D. UPDATE

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Correct Answer: Option C

Explanation:
ALTER TABLE is a DDL command used to add, delete, or modify columns and constraints in an existing table.

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

Question #58

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What is a view in a database?

A. A physical table stored on disk

B. An index on a table

C. A backup of a table

D. A virtual table based on the result of a SELECT query

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Correct Answer: Option D

Explanation:
A view is a logical representation of data, derived from one or more tables, but does not store data physically.

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

Question #59

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Which of the following is a DML statement?

A. ALTER

B. UPDATE

C. DROP

D. CREATE

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Correct Answer: Option B

Explanation:
UPDATE is a Data Manipulation Language (DML) command used to modify existing records in a table. CREATE, ALTER, DROP are DDL.

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

Question #60

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What is the default sorting order when using ORDER BY without specifying ASC or DESC?

A. Descending

B. Random

C. Ascending

D. No order

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Correct Answer: Option C

Explanation:
ORDER BY defaults to ascending (ASC) order.

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

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