How Can I Safely Use ORDER BY Parameters with PDO Prepared Statements in PHP?

PDO Prepared Statement: Setting ORDER BY Parameters

When working with SQL statements in PHP using PDO prepared statements, setting parameters in the ORDER BY clause can be tricky. Unlike other parameters, which can be bound using methods like bindParam(), PDO does not provide a direct way to specify parameters for ORDER BY.

To resolve this, it is necessary to insert the order and direction values directly into the SQL string. However, this approach has the potential to introduce SQL injection vulnerabilities if user input is not properly sanitized.

Cautionary Approach

The most secure method is to hardcode the ORDER BY criteria into the SQL string, like so:

$order = 'columnName';
$direction = 'ASC';

$query = "SELECT field from table WHERE column = :my_param ORDER BY $order $direction";

$stmt = $db->prepare($query);
$stmt->bindParam(':my_param', $is_live, PDO::PARAM_STR);
$stmt->execute();

Custom Helper Function

An alternative approach is to create a custom helper function that whitelists acceptable values for the ORDER BY parameters. This ensures that only valid values are used and mitigates the risk of SQL injection.

function white_list($value, array $whitelist, $errorMessage)
{
    if (!in_array($value, $whitelist)) {
        throw new Exception($errorMessage);
    }

    return $value;
}

$order = white_list($_GET['sort'], ["name", "price", "qty"], "Invalid field name");
$direction = white_list($_GET['direction'], ["ASC", "DESC"], "Invalid ORDER BY direction");

$sql = "SELECT field from table WHERE column = ? ORDER BY $order $direction";
$stmt = $db->prepare($sql);
$stmt->execute([$is_live]);

This helper function verifies the validity of the ORDER BY parameters and throws an exception if an invalid value is detected.

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