What is the difference between a primary key and a foreign key?
A primary key uniquely identifies each row in a table, cannot be null, and there is only one per table. A foreign key is a column in one table that points to the primary key of another table, which creates a link between the two. Primary keys enforce uniqueness, while foreign keys enforce relationships and referential integrity.
Primary key
It is the unique identity of a row, like a roll number for a student. No two rows can share it and it cannot be empty.
Foreign key
It connects tables. An orders table might store a customer id that refers to the primary key of the customers table, so each order knows which customer placed it.
CREATE TABLE customers (
id INT PRIMARY KEY,
name VARCHAR(50)
);
CREATE TABLE orders (
id INT PRIMARY KEY,
customer_id INT,
FOREIGN KEY (customer_id) REFERENCES customers(id)
);A crisp answer is a primary key identifies a row uniquely, a foreign key links to another table's primary key. Adding that a foreign key protects referential integrity, so you cannot reference a customer that does not exist, shows real database sense.
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