mysql_num_rows() 期望参数 1 是资源，布尔值在 C:\wamp\www [关闭]

Question

代码在几页上运行良好，并显示某种警告，例如“mysql_num_rows() 期望参数 1 是资源，C:\wamp\www 中给出的布尔值”......它总是让我感到困惑，因为它适用于某些页面，有时会显示一条警告消息，这让我很沮丧...请帮助...

<?php 
    $emp_id=$_SESSION['username'];
    $s=mysql_query("select semester from faculty_advisor where emp_id = '$emp_id' ");
    echo $s; //just to check if am getting the correct value
    $subject=mysql_query("select * from subject_list where semester=$s");
    $numrows=mysql_num_rows($subject);
    if($numrows!=0)
    {
        while($row=mysql_fetch_array($numrows))
        {
            ?>
        <td align="center"><?php echo  $row['sid']; ?></td>
        <td align="center"><?php echo  $row['subject_name']; ?></td>
    <td align="center"><?php echo  "<a class='tooltip' href=\"fac_adv_reg_confrm.php?uid=".$row['sid']."\">Edit<span>Edit User Details</span></a>"?></td>  
            <?php
        }
    }
    else
    {
   die('Error: ' . mysql_error());
    }

    ?>

Answer 1

$s=mysql_query("select semester from faculty_advisor where emp_id = 'macs410' ");
echo $s;
$subject=mysql_query("select * from subject_list where semester=$s");

Should be

$s=mysql_query("select semester from faculty_advisor where emp_id = 'macs410' ");
$row = mysql_fetch_assoc($s); 
$subject=mysql_query("select * from subject_list where semester='".$row['semester']."'");

Answer 2

发生这种情况是因为您的$subject=mysql_query("select * from subject_list where semester=$s"); 由于查询失败而返回FALSE，请使用mysql_error() 找出错误。

通常使用mysql_query() or die (mysql_error()) 以确保代码在出错后不会继续。

更新

我还注意到，在您的第一个查询结果$s 中，您直接使用它，就好像它是一个变量。您需要先使用mysql_fetch_assoc 或mysql_fetch_row 提取该行，然后再将其传递给第二个查询

Answer 3

 $s=mysql_query("select semester from faculty_advisor where emp_id = 'macs410' ");
 echo $s;
 $subject=mysql_query("select * from subject_list where semester=$s");

Hear $s is a resource object so 
mysql_query("select * from subject_list where semester=$s");
will give an error

hence $subject is not a valid resource object