What is the difference between a Primary Key and a Foreign Key in the context of PHP and MySQL databases?

Primary Key is a unique identifier for each record in a table, used to uniquely identify each row in the table. Foreign Key is a field in a table that is a primary key in another table, used to establish a relationship between the two tables. 

// Creating a table with a Primary Key
$sql = "CREATE TABLE users (
    id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(30) NOT NULL,
    email VARCHAR(50) NOT NULL
)";

// Creating a table with a Foreign Key
$sql = "CREATE TABLE orders (
    id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    user_id INT(6) UNSIGNED,
    total_amount DECIMAL(10,2),
    FOREIGN KEY (user_id) REFERENCES users(id)
)";

Keywords

Primary Key Foreign Key PHP MySQL databases

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