How can PHP developers ensure data consistency and avoid duplication when designing database tables for user registration and login?

To ensure data consistency and avoid duplication when designing database tables for user registration and login, PHP developers can use unique constraints on columns that should have unique values, such as email addresses or usernames. This will prevent duplicate entries in the database and maintain data integrity.

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) UNIQUE,
    email VARCHAR(100) UNIQUE,
    password VARCHAR(255)
);