Preparing SQL query

Question

In my PHP document, I got a SQL query looking like this:

if(isset($_GET['id']))
{
    $id = $_GET['id'];
    $q = "SELECT * FROM `objekt_t` WHERE `id`='" . $id . "'";
    $row = mysqli_query($con, $q) or die(mysqli_error($con));
    while($r = mysqli_fetch_assoc($row))
    {
        $objekt = $r;
    }
}

I realize this is very unsafe practice concerning SQL injections and such, so I've been looking into prepared SQL querys, using bound parameters. Looking at bobby-tables.com I see this example query:

$stmt = $db->prepare('update people set name = ? where id = ?');
$stmt->bind_param('si',$name,$id);
$stmt->execute();

I do not understand how I should modify my current query to match the safer one using bound parameters. Any help is appreciated.

Answer 1

Just the same way

$mysqli = new mysqli("localhost", "my_user", "my_password", "db");

if(isset($_GET['id']))
{
    $id = $_GET['id'];
    $q = "SELECT some_field FROM `objekt_t` WHERE `id`= ?";

    if ($stmt = $mysqli->prepare($q)) {    
        $stmt->bind_param("i", $id);
        $stmt->execute();
        $stmt->bind_result($result);
        $stmt->fetch();
    }
}

Now $result variable contains the resuts of your query.

Answer 2

prepared statements transmit raw data to the query so that SQL injection is not possible. There is no need to escape for real_escape_String or any other formatting functions, as this does it for you.

Example:

$db = new mysqli ("host","user","password","database");
$statement = $db->prepare("SELECT test FROM test WHERE Username=?");
$statement->bind_param('s',$_POST['Username']);
$statement->execute();
$statement->bind_result($resultCol);
$statement->fetch();
$statement->close();

I am basically binding my $_POST data directly to the query because the data is being sent as raw, so even if the query contained a form of injection, as the $_POST['username']; the query will run as normal.

---

IN terms of the procedure and OOP style, it's down to preference, I personlly prefer the OOP style over the other options as it's more readable.

Working with numbers:

$ID= 5;
$db = new mysqli ("host","user","password","database");
$statement = $db->prepare("SELECT test FROM test WHERE ID=?");
$statement->bind_param('i',$ID);
$statement->execute();
$statement->bind_result($resultCol);
$statement->fetch();
$statement->close();

Or you can work with exact values directly within the statement:

$db = new mysqli ("host","user","password","database");
$statement = $db->prepare("SELECT test FROM test WHERE ID='5'");
$statement->execute();
$statement->bind_result($resultCol);
$statement->fetch();
$statement->close();

Answer 3

You can do it like this:

$stmt = $mysqli->prepare('SELECT * FROM objekt_t WHERE id = ?');
$stmt->bind_param('i', $id);
$stmt->execute();

$result = $stmt->get_result();

while ($row = $result->fetch_assoc()) {
    // $row is an associative array
}