PHP动态登录无法正常工作

Question

正在使用登录表单但是当我尝试var_dump我的sql

时它不起作用

<?php
session_start();
include ('database.php');
if (isset($_POST['login'])) {
    $user = $_POST['username'];
    $pass = sha1($_POST['pass']);
    $sql = "SELECT * FROM users WHERE pass = sha1('$pass') 
                              AND username = '$user'";
    $query = mysqli_query($conn,$sql);
    $results = mysqli_num_rows($query);
    //die(var_dump($results));
    if ($results == 1) {
        $_SESSION['username']=$user;
    }
    header('location: index.php');
}
?>