CS Database Management & SQL 3

Question 1

Which SQL command permanently removes a table and all of its data and structure?

Accepted Answer

DROP TABLE

Answer

DROP TABLE deletes both the table's data and its definition from the database.

Question 2

A foreign key constraint enforces which type of integrity?

Accepted Answer

Referential integrity

Answer

Foreign keys ensure a value in one table matches an existing key in the referenced table.

Question 3

Which query returns employees whose salary is above the company average?

Accepted Answer

SELECT name FROM emp WHERE salary > (SELECT AVG(salary) FROM emp);

Answer

Aggregate functions cannot appear directly in WHERE, so a subquery computes the average first.

Question 4

What is the main purpose of a database index?

Accepted Answer

Speed up data retrieval at the cost of extra storage and slower writes

Answer

Indexes accelerate lookups but add storage overhead and slow INSERT/UPDATE operations.

Question 5

Which statement about SQL UNION vs UNION ALL is correct?

Accepted Answer

UNION removes duplicate rows while UNION ALL keeps them

Answer

UNION performs duplicate elimination, making UNION ALL faster when duplicates are acceptable.

(CS) Computer Science Practice Test