php - 警告 : mysql_num_rows(): supplied argument is not a valid

Question

您好，我收到以下错误，我仔细检查了所有内容，但不知道为什么会显示它。 警告:mysql_num_rows():提供的参数不是第 6 行/home/namebob/public_html/site_reg/statlookup.php 中的有效 MySQL 结果资源

<?php
    include_once('common.php');
    $cid        =   $_REQUEST['cid'];
    $_elmID     =   $_REQUEST['elmID'];
    $scan = mysql_query("SELECT  `id`, `state` FROM `mast_state` WHERE `countryid` = $cid");
    if(mysql_num_rows($scan)>0)
    {
...

Answer 1

$scan = mysql_query("SELECT  `id`, `state` FROM `mast_state` WHERE `countryid` = $cid");
    $stock_num = '';
    if($scan )
    {
        while($row=mysql_fetch_object($scan))
        {
            if($row->state)
            $state  = $row->state;
        }   
    }