How can PHP be used to validate form data against values stored in a MySQL database?

To validate form data against values stored in a MySQL database using PHP, you can first retrieve the values from the database and then compare them with the submitted form data. This can help ensure that the data entered by the user is valid and matches existing records in the database. 

// Connect to MySQL database
$connection = mysqli_connect("localhost", "username", "password", "database");

// Retrieve form data
$username = $_POST['username'];
$password = $_POST['password'];

// Query database for user with matching credentials
$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($connection, $query);

// Check if a matching user was found
if(mysqli_num_rows($result) > 0) {
    // User credentials are valid
    echo "Login successful!";
} else {
    // User credentials are invalid
    echo "Invalid username or password.";
}

// Close database connection
mysqli_close($connection);

Keywords

PHP form validation MySQL database data validation error handling

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