Why is it advised against storing multiple values separated by commas in a database field in PHP?

Storing multiple values separated by commas in a database field in PHP is not recommended because it violates database normalization principles, making it difficult to query and manipulate the data efficiently. Instead, it is better to create a separate table to store the multiple values in a relational manner using foreign keys to establish relationships between the tables.

// Create a separate table to store multiple values in a relational manner
CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(50)
);

CREATE TABLE user_values (
    id INT PRIMARY KEY,
    user_id INT,
    value VARCHAR(50),
    FOREIGN KEY (user_id) REFERENCES users(id)
);