这对我很管用。确保你所有的 if 这是真的。

$link = mysqli_connect("localhost","root","root","test");

if(isset($_POST['logg'])){
    $login = $_POST['login'];
    $pasw = $_POST['password'];
    if(empty($login)||empty($pasw)){
        echo '<script language="javascript">';
        echo 'alert("Lracnel dashty")';
        echo '</script>';
    }
    else {
        $sql = "SELECT  `login` ,  `password` FROM  `contact_form` WHERE login = '$login' AND password = '$pasw'";
        $result = mysqli_query($link,$sql);
        while ($lol = mysqli_fetch_assoc($result)) {
            if($login==$lol['login']){
                if($pasw==$lol['password']){
                    echo 'Welcome '.$lol['login'];
                }
                else{
                    echo 'Wrong password';
                }
            }
            else{
                echo 'Wrong login';
                break;
            }
        }
    }
}

我建议你用 PDO 为了查询数据库，我修改了您的代码以添加 WHERE 子句和要使用password\u verify（）php函数，这意味着您将在将密码保存到数据库之前对其进行哈希处理，您还需要在查询数据库之前对输入进行清理。

<?php
        $link = mysqli_connect("localhost","root","root","test");
        if(isset($_POST['logg'])){
            $login = $_POST['login'];
            $pasw = $_POST['password'];
            if(empty($_POST['login'])||empty($_POST['password'])){
                echo '<script language="javascript">';
                echo 'alert("Lracnel dashty")';
                echo '</script>';
            }
            else {
                // Don't forget to sanitize your input before the query
                $sql = "SELECT  login, password 
                FROM contact_form WHERE login = $login ";

                $result = mysqli_query($link,$sql);
                while ($lol = mysqli_fetch_assoc($result)) {
                    if($login==$lol['login']){
                        if(password_verify($pasw, $lol['password'])){
                            echo 'Welcome '.$lol['login'];

                        }
                        else{
                            echo 'Wrong password';

                        }
                    }
                    else{
                        echo 'Wrong login';
                        break;
                    }
                }
            }

        }
    ?>