What are some common mistakes to avoid when working with PHP and MySQL databases?

One common mistake to avoid when working with PHP and MySQL databases is not properly sanitizing user input before querying the database. This can lead to SQL injection attacks where malicious code is injected into your queries. To prevent this, always use prepared statements or parameterized queries to safely interact with the database. 

// Incorrect way to query the database without sanitizing user input
$username = $_POST['username'];
$password = $_POST['password'];
$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($conn, $query);

// Correct way to use prepared statements to sanitize user input
$username = $_POST['username'];
$password = $_POST['password'];
$query = "SELECT * FROM users WHERE username=? AND password=?";
$stmt = $conn->prepare($query);
$stmt->bind_param("ss", $username, $password);
$stmt->execute();
$result = $stmt->get_result();

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