How can one improve the database design in the provided code snippet to avoid potential issues and improve performance?

Issue: The current database design in the code snippet does not include proper indexing on the columns used for searching and filtering data, which can lead to slow query performance. To improve the database design and performance, we can add indexes on the columns that are frequently used in WHERE clauses.

// Improved database design with proper indexing
CREATE TABLE users (
    id INT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    INDEX idx_username (username),
    INDEX idx_email (email)
);