What potential improvement was suggested for the PHP script in terms of efficiency?

The potential improvement suggested for the PHP script in terms of efficiency is to use prepared statements when interacting with the database to prevent SQL injection attacks and improve performance. Prepared statements allow the database to compile the query once and execute it multiple times with different parameters, reducing the overhead of parsing and optimizing the query each time.

// Original code
$sql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
$result = mysqli_query($conn, $sql);

// Improved code using prepared statements
$stmt = $conn->prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt->bind_param("ss", $username, $password);
$stmt->execute();
$result = $stmt->get_result();