警告：mysql_num_rows（）希望参数1是resource，布尔值在第17行的/var/customers/webs/ni272979_1/Loader/login.php中给出

您的查询中有一个错误。应该是这样的

<?php
$filename = 'install.php';
if (file_exists($filename)) {
echo ("<center><font color='red'><b>/install.php still exists<br>
After installing please delete install.php</center></font></b>");
} else {
if (isset($_POST['Login'])){
include('config.php');
    if (!mysql_connect($host, $username, $password)) die("Can't connect to database");
    if (!mysql_select_db($db_name)) die("Can't select database");
    $myusername=$_POST['myusername'];
    $mypassword=$_POST['mypassword'];

    $sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword' or die(mysql_error());";
    $result=mysql_query($sql);
    $count=mysql_num_rows($result);
    if($count >= 1){
    session_register("myusername");
    session_register("mypassword");
    header("location: index.php");
    } else {

    }
}

$sql = "SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword';";

然后你可以这样做

<?php
$filename = 'install.php';
if (file_exists($filename)) {
echo ("<center><font color='red'><b>/install.php still exists<br>
After installing please delete install.php</center></font></b>");
} else {
if (isset($_POST['Login'])){
include('config.php');
    if (!mysql_connect($host, $username, $password)) die("Can't connect to database");
    if (!mysql_select_db($db_name)) die("Can't select database");
    $myusername=$_POST['myusername'];
    $mypassword=$_POST['mypassword'];

    $sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword' or die(mysql_error());";
    $result=mysql_query($sql);
    $count=mysql_num_rows($result);
    if($count >= 1){
    session_register("myusername");
    session_register("mypassword");
    header("location: index.php");
    } else {

    }
}

$sql = "SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword';";

---

还可以尝试使用或函数进行CRUD操作。

请阅读。不应使用不推荐使用的

mysql_*（）

函数编写新代码。相反，现在是开始学习如何使用MySQLi或PDO安全地使用

prepare（）/execute（）

。请学习如何不存储密码（1的纯文本）：如果您正在学习某个特定教程，最好找到一个更新的教程。也