当我使用Netbeans进行调试时，无法执行DELETION，因为 $ test_affected_rows = mysqli_affected_rows（$ dbc）将返回-1。这很奇怪，因为我只是运行脚本，删除运行良好。 在调试模式下，mysqli_affected_rows（$ dbc）始终返回-1（应为1）。到底是什么原因？
require ('./mysqli_connect.php');
// Check if the form has been submitted:
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
if ($_POST['sure'] == 'Yes') { // Delete the record.
// Make the query:
$q = "DELETE FROM users WHERE user_id=$id LIMIT 1";
$r = @mysqli_query ($dbc, $q);
$test_affected_rows= mysqli_affected_rows($dbc);
if ($test_affected_rows == 1) { // If it ran OK.
// Print a message:
echo '<p>The user has been deleted.</p>';
} else { // If the query did not run OK.
echo '<p class="error">The user could not be deleted due to a system error.</p>'; // Public message.
echo '<p>' . mysqli_error($dbc) . '<br />Query: ' . $q . '</p>'; // Debugging message.
}
}