Cognizant Database Management Systems

Question 1

Which of the following best defines a primary key in a relational database?

Accepted Answer

A unique identifier for each record in a table

Answer

A column that can contain NULL values

Answer

A key that references another table

Answer

A key used only for sorting records

Question 2

Which SQL clause is used to filter records after a GROUP BY has been applied?

Accepted Answer

HAVING

Answer

WHERE

Answer

FILTER

Answer

ORDER BY

Question 3

What is the primary goal of database normalization?

Accepted Answer

To eliminate data redundancy and improve data integrity

Answer

To increase query execution speed

Answer

To add more tables to the database

Answer

To allow duplicate records for backup

Question 4

Which type of JOIN returns all rows from both tables, with NULLs where there is no match?

Accepted Answer

FULL OUTER JOIN

Answer

INNER JOIN

Answer

LEFT JOIN

Answer

RIGHT JOIN

Question 5

In the context of ACID properties, what does 'Atomicity' mean?

Accepted Answer

A transaction is treated as a single unit — all or nothing

Answer

Data remains consistent before and after a transaction

Answer

Transactions are isolated from each other

Answer

Data is permanently saved after a commit

Question 6

Which SQL command is used to remove a table and all its data permanently from the database?

Accepted Answer

DROP

Answer

DELETE

Answer

TRUNCATE

Answer

REMOVE

Question 7

What is a foreign key?

Accepted Answer

A column that references the primary key of another table

Answer

A key imported from an external database

Answer

A primary key stored in encrypted form

Answer

A unique key shared across multiple tables