PHP mySQL 错误

Question

我是 php 新手，所以我决定关注 this tutorial一个简单的登录屏幕。我设置了代码，但是当我尝试登录时出现此错误:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in (a long file path to the script) on line 27

我从教程中得到的代码是:

<?php
ob_start();
$host="thehost"; // Host name
$username="myusername"; // Mysql username 
 $password="mypass"; // Mysql password 
 $db_name="test"; // Database name 
 $tbl_name="members"; // Table name

// Connect to server and select databse.
 mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
 mysql_select_db("$db_name")or die("cannot select DB");

// Define $myusername and $mypassword 
 $myusername=$_POST['myusername']; 
 $mypassword=$_POST['mypassword'];

// To protect MySQL injection (more detail about MySQL injection)
 $myusername = stripslashes($myusername);
 $mypassword = stripslashes($mypassword);
 $myusername = mysql_real_escape_string($myusername);
 $mypassword = mysql_real_escape_string($mypassword);

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

// Mysql_num_row is counting table row
 $count=mysql_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row

 if($count==1){
// Register $myusername, $mypassword and redirect to file "login_success.php"
 session_register("myusername");
 session_register("mypassword"); 
 header("location:login_success.php");
}
 else {
 echo "Wrong Username or Password";
}

 ob_end_flush();
?>

(注:mySQL数据库信息全部填写在我的版本上)

另外，作者给出了一个php5版本和一个普通的php版本。我都试过了，但得到了同样的错误。如果有人知道为什么会发生这种情况，我们将不胜感激。

Answer 1

您可以打印$sql 变量并自己尝试查询，或者使用mysql_error() 打印mysql 错误。 这个查询似乎失败了。