php - mysql_num_rows PHP

Question

elseif(isset($_POST['submit']))
{
    // Look for their user
    $lookuser = mysql_query("SELECT * FROM `users` WHERE username='". mysql_escape_string($_POST['username']) ."'");
    // If we find a row
    if(mysql_num_rows($lookuser) > 0)

但我的其他方面，回响:An error has occured. <br> If you are sure you entered your username correctly, please contact an administrator.

我尝试回显 $_POST['username'];一切顺利。我已经确保我的用户存在，效果很好。

我得到的 PHP 错误: Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in password.php on line 23

Answer 1

Php.net关于 mysql_query 的返回值是这样说的:

For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.

如果你得到一个 bool 值，那是因为存在 mysql 错误。使用mysql_error()打印错误，它将帮助您诊断问题。