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 primary key uniquely identifies each record in a table and cannot contain NULL values.

Question 2

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

Accepted Answer

HAVING

Answer

HAVING is used to filter groups after GROUP BY, whereas WHERE filters individual rows before grouping.

Question 3

What is the primary goal of database normalization?

Accepted Answer

To eliminate data redundancy and improve data integrity

Answer

Normalization organizes data to reduce redundancy and dependency, improving data integrity and storage efficiency.

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

FULL OUTER JOIN returns all rows from both tables, filling unmatched rows with NULL values.

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

Atomicity ensures that all operations in a transaction are completed successfully; if any operation fails, the entire transaction is rolled back.

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