How Can I Securely Use ORDER BY in Prepared PDO Statements?

Setting ORDER BY Parameters in Prepared PDO Statements

When attempting to use parameters in the ORDER BY section of an SQL query using a prepared PDO statement, it's important to be aware that PDO does not support directly binding column names or ordering directions as parameters. This can lead to confusion when the desired sorting order is not applied.

To resolve this issue, you must insert the ORDER BY clause directly into the SQL query, as illustrated in the following example:

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

$stmt = $db->prepare("SELECT * from table WHERE column = :my_param ORDER BY $order $direction");

Escaping Considerations

It's crucial to ensure that every operator and identifier in the ORDER BY clause is hardcoded in your script to prevent security vulnerabilities. Never interpolate user-supplied input directly into the ORDER BY clause.

Whitelisting Helper Function

To simplify the validation and whitelisting process, you can create a helper function:

function white_list($value, $allowed, $error) {
  if (in_array($value, $allowed)) {
    return $value;
  } else {
    throw new Exception($error);
  }
}

This function checks the value against a list of allowed options and raises an error if the value is invalid.

Usage

With the whitelisting helper function, you can create a secure prepared statement for the ORDER BY clause:

$order = white_list($order, ["name","price","qty"], "Invalid field name");
$direction = white_list($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]);

By following these guidelines, you can correctly set ORDER BY parameters in prepared PDO statements while maintaining security.

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