What is the difference between a primary key and a foreign key?

• Primary Key: A unique identifier for each record in a database table. No two rows in

a table can have the same primary key value. It ensures entity integrity.

Example: user_id in a users table.

• Foreign Key: A field (or a combination of fields) in one table that uniquely identifies a

row of another table. It establishes a relationship between two tables and enforces

referential integrity.

Example: user_id in an orders table linking to user_id in the users table.