DBMS MCQs with Answers and Explanations

Question #101

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Which of the following is a valid way to join three tables in SQL?

A. SELECT * FROM table1, table2, table3 WHERE condition1 AND condition2;

B. SELECT * FROM table1 JOIN table2 ON condition1 JOIN table3 ON condition2;

C. Both A and B

D. Neither

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Correct Answer: Option C

Explanation:
Both syntaxes are valid: explicit JOIN syntax and implicit comma join with WHERE conditions.

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

Question #102

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What is the purpose of the SQL COALESCE function?

A. Computes the sum

B. Concatenates strings

C. Converts data types

D. Returns the first non-NULL value from a list

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Correct Answer: Option D

Explanation:
COALESCE returns the first non-NULL value among its arguments, often used to provide a default value.

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

Question #103

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Which normal form enforces that no non-prime attribute depends on a subset of a candidate key?

A. 2NF

B. 3NF

C. BCNF

D. 1NF

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Correct Answer: Option A

Explanation:
2NF eliminates partial dependencies, i.e., non-prime attributes dependent on part of any candidate key.

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

Question #104

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What is a database transaction?

A. A query that reads data

B. A backup copy of the database

C. A database schema

D. A logical unit of work that consists of one or more SQL statements

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Correct Answer: Option D

Explanation:
A transaction is a sequence of operations performed as a single logical unit, ensuring ACID properties.

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

Question #105

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Which of the following is true about a surrogate key?

A. It is an artificial key, usually an auto-increment integer, with no business meaning

B. It is a natural key derived from the data

C. It is a foreign key

D. It is a composite key

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Correct Answer: Option A

Explanation:
A surrogate key is a system-generated unique identifier, typically numeric, that has no business significance.

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

Question #106

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What is the purpose of the SQL GROUP BY ... HAVING combination?

A. To join groups

B. To filter groups based on aggregate values

C. To sort groups

D. To select individual rows

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Correct Answer: Option B

Explanation:
HAVING is used in conjunction with GROUP BY to filter groups based on conditions applied to aggregate functions.

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

Question #107

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Which of the following is not an aggregate function in SQL?

A. DESC

B. SUM

C. MAX

D. AVG

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Correct Answer: Option A

Explanation:
DESC is a keyword for sorting order, not an aggregate function.

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

Question #108

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What is a foreign key constraint violation?

A. Updating a primary key that is referenced

B. All of the above

C. Inserting a value in a foreign key column that does not exist in the referenced primary key

D. Deleting a primary key that is referenced by a foreign key

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Correct Answer: Option B

Explanation:
Any action that breaks referential integrity, such as inserting an orphan record, deleting a referenced record, or updating a referenced key, will violate the foreign key constraint.

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

Question #109

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Which SQL statement is used to delete all rows from a table without logging individual row deletions?

A. REMOVE FROM table_name;

B. DELETE FROM table_name;

C. DROP TABLE table_name;

D. TRUNCATE TABLE table_name;

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Correct Answer: Option D

Explanation:
TRUNCATE TABLE removes all rows and is a DDL operation with minimal logging, often faster than DELETE without WHERE.

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

Question #110

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What is a database schema?

A. The overall design or structure of the database, including tables, columns, and relationships

B. A query result

C. A backup file

D. A single table

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Correct Answer: Option A

Explanation:
A schema is the logical description of the entire database, defining tables, views, indexes, and constraints.

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

Question #111

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What is the difference between a database and a data warehouse?

A. Databases are for OLTP, data warehouses for OLAP

B. They are the same

C. Both A and B

D. Databases store current data; data warehouses store historical data

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Correct Answer: Option C

Explanation:
Databases are optimized for transaction processing (OLTP), while data warehouses are designed for analytical reporting (OLAP) using historical data.

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

Question #112

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Which of the following is a valid SQL data type for a date and time?

A. DATETIME

B. TIMESTAMP

C. All of the above

D. DATE

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Correct Answer: Option C

Explanation:
Different DBMS support DATETIME, TIMESTAMP, DATE, etc. All are valid date/time types.

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

Question #113

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What is the purpose of the SQL 'UNION' operator?

A. To filter duplicates

B. To combine the results of two or more SELECT statements, removing duplicates

C. To aggregate data

D. To join tables horizontally

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Correct Answer: Option B

Explanation:
UNION concatenates the result sets of two or more queries, eliminating duplicate rows. UNION ALL keeps duplicates.

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

Question #114

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Which SQL operator is used to check if a value is within a range?

A. LIKE

B. BETWEEN

C. EXISTS

D. IN

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Correct Answer: Option B

Explanation:
BETWEEN checks if a value falls within a specified range (inclusive of boundaries).

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

Question #115

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What is a domain in the context of the relational model?

A. A set of allowed values for an attribute

B. A foreign key

C. A table name

D. A primary key

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Correct Answer: Option A

Explanation:
A domain defines the set of permissible values that an attribute can take, ensuring data consistency.

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

Question #116

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Which of the following is a property of a database that ensures transactions are isolated from each other?

A. Isolation

B. Atomicity

C. Consistency

D. Durability

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Correct Answer: Option A

Explanation:
Isolation ensures that concurrent execution of transactions results in a state that is equivalent to some serial execution.

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

Question #117

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What is a candidate key in a relation?

A. A foreign key

B. A super key that is minimal

C. Any column that can be used as a primary key

D. A key that is not unique

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Correct Answer: Option B

Explanation:
A candidate key is a minimal super key, meaning no subset of it can uniquely identify a row.

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

Question #118

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Which of the following is an example of a NoSQL database?

A. MySQL

B. Oracle

C. PostgreSQL

D. MongoDB

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Correct Answer: Option D

Explanation:
MongoDB is a document-oriented NoSQL database. PostgreSQL, MySQL, and Oracle are RDBMS.

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

Question #119

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What is the purpose of the SQL 'CASE' statement?

A. To implement conditional logic within a query

B. To update records

C. To create a table

D. To delete records

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Correct Answer: Option A

Explanation:
CASE allows for conditional expressions, similar to IF-THEN-ELSE, within SQL statements.

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

Question #120

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In SQL, what does the 'IS NULL' operator check?

A. Whether a value is missing (null)

B. Whether a value equals NULL

C. Whether a value is empty string

D. Whether a value is zero

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Correct Answer: Option A

Explanation:
IS NULL is used to test for NULL values, because NULL is not equal to anything.

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

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