Quiz for Primary Key vs Foreign Key

Q1: Which key uniquely identifies a row in a table?

A. Foreign Key B. Candidate Key C. Primary Key D. Composite Key

Q2: What is the purpose of a primary key in a table?

A. To allow duplicates B. To reference another table C. To uniquely identify each row D. To increase performance

Q3: What is the purpose of a Primary Key in a database?

A. To uniquely identify each record in a table B. To link two tables C. To store duplicate values D. To allow null values

Q4: Which of the following can have NULL values?

A. Primary Key B. Foreign Key C. Both D. None

Q5: Can a table have more than one Foreign Key?

A. Yes B. No C. Only if it is also a Primary Key D. Only one per database

Q6: Which key creates a relationship between two tables?

A. Primary Key B. Foreign Key C. Composite Key D. Unique Key

Q7: Which key must contain unique and non-null values?

A. Primary Key B. Foreign Key C. Composite Key D. Candidate Key

Q8: Which of the following is FALSE about Primary Key?

A. Primary Key must be unique B. Primary Key can be NULL C. Primary Key can be a single column or a combination D. Primary Key is used to identify records

Q9: What happens when you delete a referenced Primary Key record?

A. The Foreign Key is updated automatically B. The referencing Foreign Key record is also deleted (if ON DELETE CASCADE) C. An error always occurs D. Nothing happens

Q10: Can a Foreign Key reference a non-primary key column?

A. Yes, if that column has a UNIQUE constraint B. No, it must always reference a Primary Key C. Only in PostgreSQL D. Only in NoSQL databases

Q11: What is the main role of a Foreign Key?

A. To uniquely identify rows in its own table B. To enforce referential integrity C. To ensure only positive values D. To auto-increment IDs

Q12: Which combination is valid in a table?

A. Multiple Primary Keys B. One Primary Key and multiple Foreign Keys C. Only Foreign Keys D. Primary Key with NULL values

Q13: Can a Foreign Key be part of a composite Primary Key?

A. Yes B. No C. Only in MySQL D. Only in NoSQL

Q14: Which type of key helps avoid redundancy across tables?

A. Primary Key B. Foreign Key C. Composite Key D. Default Key

Q15: What is required before adding a Foreign Key?

A. The referenced column must be a Primary or Unique Key B. The table must be empty C. The key must be indexed D. You must disable constraints

Q16: Which constraint is automatically indexed?

A. Foreign Key B. Primary Key C. Check D. Default

Q17: Can a table have both Primary Key and Foreign Key?

A. Yes B. No C. Only if both are composite keys D. Only in Oracle DB

Q18: What does referential integrity ensure?

A. Foreign Key values must match values in referenced Primary Key B. No duplicate rows are allowed C. Each row must have a unique value D. Column names must be same across tables

Q19: Which one helps maintain relationships between entities?

A. Primary Key B. Foreign Key C. Both D. None

Q20: Is it possible for a Foreign Key to reference another Foreign Key?

A. Yes B. No C. Only if both are indexed D. Only in MySQL 8.0+

Q21: Which action is not allowed on a Primary Key column?

A. Insert NULL B. Add Index C. Reference from another table D. Use in WHERE clause

Q22: What is the default behavior when a referenced Primary Key is deleted and no ON DELETE clause is set?

A. The referencing row is deleted B. Nothing happens C. Referential integrity error occurs D. It is automatically updated to NULL