B.S.W.E. Bachelor of Software Engineering Database Systems & SQL 2

Question 1

What is a database index and what does it improve?

Accepted Answer

A data structure that improves query performance

Answer

A database index is a data structure that provides fast lookup of data based on column values, significantly improving SELECT query performance.

Question 2

What does the GROUP BY clause do in SQL?

Accepted Answer

Groups rows sharing a common value for aggregate functions

Answer

GROUP BY groups rows that have the same values in specified columns, enabling aggregate functions like COUNT, SUM, and AVG per group.

Question 3

What is a stored procedure in SQL?

Accepted Answer

A precompiled set of SQL statements stored in the database

Answer

A stored procedure is a precompiled collection of SQL statements that can be executed as a single named unit, improving performance and reusability.

Question 4

What is the difference between WHERE and HAVING in SQL?

Accepted Answer

WHERE filters before grouping; HAVING filters after grouping

Answer

WHERE filters individual rows before aggregation, while HAVING filters groups after the GROUP BY clause has been applied.

Question 5

What is a database view?

Accepted Answer

A virtual table based on a SELECT query

Answer

A view is a virtual table defined by a stored SQL query that can be queried like a regular table but stores no data itself.

B.S.W.E. Bachelor of Software Engineering Practice Test