Q02. What is a primary key?
A primary key uniquely identifies each row and cannot contain NULL. A table has one primary key constraint, which may include multiple columns.
Interview tip: explain the core behavior, then mention one operational trade-off or edge case.
Note
Interview approach: define the concept, explain when you use it, and mention one limitation or production consideration.
Concept example
-- Demonstrate the concept with a small query or schema example
SELECT current_database();💡 This short query illustrates the PostgreSQL environment used during examples. In an interview, adapt the example to the specific concept and explain the underlying behavior.
Key Takeaways
- Give a concise definition.
- Explain a real-world use case.
- Mention one trade-off or safety consideration.
Knowledge Check
Can a composite primary key contain multiple columns?