DBC - CH03

Your university stores each student’s ID, name, and course in a table. What key ensures no duplicate student IDs exist?

• Foreign Key

• Composite Key

• Primary Key

• Secondary Key

In a ride-hailing app, a driver can complete many trips, but each trip is linked to only one driver. What kind of relationship is this?

• M:N

• 1:1

• Recursive

• 1:M

Which key is used only for data retrieval and not for entity identification?

• Super Key

• Primary Key

• Composite Key

• Secondary Key

You're designing a database for a smart fridge that tracks expiry dates of items. Which attribute would most likely allow NULL values?

• Item Name

• Expiry Date

• Storage Temperature

• Disposal Date

Which key contains minimum required attributes to uniquely identify a row?

• Candidate Key

• Super Key

• Composite Key

• Foreign Key

Why should NULLs be avoided in primary keys?

• They confuse programmers

• They slow down queries

• They violate uniqueness

• They make data visually messy

A mobile wallet links user payments to bank accounts. Which key ensures each payment references the correct bank account?

• Composite Key

• Primary Key

• Foreign Key

• Candidate Key

Which type of relationship cannot be directly implemented in the relational model?

• 1:1

• 1:M

• M:N

• Self-join

What happens if a foreign key value doesn’t match any primary key in the referenced table?

• Nothing

• Referential integrity is violated

• Table is deleted

• Index is corrupted

You are building a library system. Each book has one ISBN. Some books have two authors. What model would help represent this?

• Add ISBN to author table

• Use 1:1 relationship

• Implement M:N with a junction table

• Use NULLs for second author