BSCS : Database Management Systems 3

Question 1

Which join returns only rows that have matching values in both tables?

Accepted Answer

INNER JOIN

Answer

INNER JOIN returns only the rows where the join condition is satisfied in both tables.

Question 2

What is a phantom read in database transactions?

Accepted Answer

A new row appearing in repeated queries due to another transaction's insert

Answer

A phantom read occurs when a transaction re-executes a query and finds new rows inserted by a concurrent transaction.

Question 3

Which SQL command permanently removes a table and its structure from the database?

Accepted Answer

DROP

Answer

DROP TABLE removes the table definition and all its data permanently, unlike DELETE which only removes rows.

Question 4

In an ER diagram, a double rectangle represents a:

Accepted Answer

Weak entity

Answer

A weak entity is drawn with a double rectangle because it cannot be uniquely identified without a related strong entity.

Question 5

Which index structure is best suited for range queries?

Accepted Answer

B+ tree index

Answer

B+ tree indexes maintain sorted order, making them efficient for range queries by traversing leaf-node linked lists.

BSCS - Bachelor of Science in Computer Science Practice Test