PRIMARY KEY

The PRIMARY KEY constraint is a combination of the NOT NULL and UNIQUE constraints. It ensures that a column cannot have a NULL value and that all values in the column are unique. The PRIMARY KEY constraint is often used to uniquely identify each row in a table. For example, consider a table products with a column product_id that should be unique and not NULL. The PRIMARY KEY constraint can be applied as follows:

CREATE TABLE products (
    product_id INT PRIMARY KEY,
    product_name VARCHAR(50),
    price DECIMAL(10, 2)
);

In this case, the product_id column must have a unique value for every row in the products table, and it cannot be NULL.

name	type
product_id	INT
product_name	VARCHAR(50)
price	DECIMAL(10, 2)

In the table above, each row has a unique value for the product_id column, as required by the PRIMARY KEY constraint.