Can you explain what a primary key in a database is and how it is used?

A Primary Key in a database is a unique identifier for each record in a table. It guarantees that each row can be uniquely identified.

Main properties of a primary key:

• Uniqueness: primary key values do not repeat.
• Cannot be NULL: each record must have a primary key value.

The primary key is used for:

• Fast data search and access.
• Table relationships through foreign keys.

Example in SQL:

CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100)
);

Here, id is the primary key, uniquely identifying each user.