DBMS MCQs

Question 1

What is a candidate key in a relational database?

Accepted Answer

Any minimal set of attributes that can uniquely identify a row

Answer

Any foreign key referencing another table

Answer

A key made up of exactly two columns

Answer

A key that allows duplicate values

Question 2

In a database, what does referential integrity ensure?

Accepted Answer

That a foreign key value always matches an existing primary key value in the referenced table

Answer

That every column has a unique value

Answer

That tables are automatically normalized

Answer

That queries run faster

Question 3

Which SQL statement is used to remove a table's structure along with all its data?

Accepted Answer

DROP TABLE

Answer

DELETE TABLE

Answer

TRUNCATE TABLE

Answer

REMOVE TABLE

Question 4

What is the main purpose of an index in a database table?

Accepted Answer

To speed up data retrieval at the cost of some extra storage and slower writes

Answer

To enforce that a column only accepts unique values

Answer

To automatically back up the table

Answer

To convert the table into a normalized form

Question 5

Which isolation level allows a transaction to read data that has been modified but not yet committed by another transaction?

Accepted Answer

Read Uncommitted

Answer

Read Committed

Answer

Repeatable Read

Answer

Serializable

Question 6

What is a deadlock in the context of database transactions?

Accepted Answer

A situation where two or more transactions are waiting on each other to release locks, with none able to proceed

Answer

A situation where a transaction takes too long to complete

Answer

A query that returns no rows

Answer

A table that has no primary key

Question 7

Which type of SQL join returns only the rows that have matching values in both tables?

Accepted Answer

INNER JOIN

Answer

LEFT JOIN

Answer

RIGHT JOIN

Answer

FULL OUTER JOIN

Question 8

What is denormalization typically used for?

Accepted Answer

To improve read performance by intentionally introducing redundancy

Answer

To remove all duplicate rows from a table

Answer

To convert a table into 3NF

Answer

To enforce stricter data integrity rules

Question 9

In the context of database keys, what is a composite key?

Accepted Answer

A primary key made up of two or more columns combined

Answer

A key that references another table

Answer

A key generated automatically by the database

Answer

A key that can contain NULL values

Question 10

What does the term ACID stand for in database transactions?

Accepted Answer

Atomicity, Consistency, Isolation, Durability

Answer

Accuracy, Consistency, Integrity, Dependency

Answer

Atomicity, Concurrency, Isolation, Dependency

Answer

Accuracy, Concurrency, Integrity, Durability

Question 11

What is a view in SQL?

Accepted Answer

A virtual table based on the result of a stored query

Answer

A physical copy of a table

Answer

A type of index

Answer

A backup of the database

Question 12

Which normal form deals specifically with removing transitive dependencies?

Accepted Answer

Third Normal Form (3NF)

Answer

First Normal Form (1NF)

Answer

Second Normal Form (2NF)

Answer

Boyce-Codd Normal Form (BCNF)

Question 13

What is the purpose of a foreign key in a relational database?

Accepted Answer

To link a column in one table to the primary key of another table

Answer

To automatically sort table rows

Answer

To store encrypted data

Answer

To prevent a table from being deleted

Question 14

What is the difference between a clustered and a non-clustered index?

Accepted Answer

A clustered index determines the physical storage order of rows, while a non-clustered index does not

Answer

A clustered index is faster but never used in practice

Answer

A non-clustered index can only be created on the primary key

Answer

There is no real difference between them

Question 15

What does the SQL GROUP BY clause do?

Accepted Answer

Groups rows that share values in specified columns so aggregate functions can be applied to each group

Answer

Sorts the result set in ascending order

Answer

Removes duplicate rows from the result

Answer

Filters rows before any aggregation happens

Question 16

What is a self join used for?

Accepted Answer

Joining a table to itself to compare rows within the same table

Answer

Joining two databases together

Answer

Merging two identical tables into one

Answer

Joining a table with a view

Question 17

Which of the following best describes a primary key?

Accepted Answer

A column or set of columns that uniquely identifies each row and cannot contain NULL values

Answer

Any column that contains only numeric data

Answer

A column used only for sorting results

Answer

A key that can be duplicated across rows

Question 18

What is the purpose of the HAVING clause in SQL?

Accepted Answer

To filter groups of rows after GROUP BY has been applied, often based on aggregate results

Answer

To filter individual rows before any grouping happens

Answer

To sort grouped results alphabetically

Answer

To rename columns in the output

Question 19

What is a stored procedure?

Accepted Answer

A precompiled set of SQL statements saved in the database and executed as a single unit

Answer

A backup copy of a table

Answer

A type of foreign key constraint

Answer

A temporary table created during a query

Question 20

In database design, what is a many-to-many relationship typically implemented with?

Accepted Answer

A junction table containing foreign keys to both related tables

Answer

A single shared primary key

Answer

A composite column storing both values

Answer

A view joining the two tables

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DBMS MCQ Questions