PHP查询数据库数据时出现异常

PHP查询数据库数据时出现错误
PHP 查询数据库books中的books表时出现以下错误！

Notice: Trying to get property of non-object in D:\wamp\Apache\htdocs\php\results.php on line 33

Fatal error: Call to a member function fetch_assoc() on a non-object in D:\wamp\Apache\htdocs\php\results.php on line 35


代码如下：

PHP code

<!--

Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/

-->

    
        <title> Book-O-Rama Catalog Search</title>
    
    
        <h1 id="Book-O-Rama-Catalog-Search">Book-O-Rama Catalog Search</h1>
<?php //create short variable names
    $searchtype=$_POST['searchtype'];
    $searchterm=trim($_POST['searchterm']);    
    
    if (!$searchtype || !$searchterm)    {
        exit('You have not entered search detais,please go back again');
    }
     
    if (!get_magic_quotes_gpc()){    
        
        $searchtype=addslashes($searchtype);
        $searchterm=addslashes($searchterm);
    }
    
    
    @ $db=new mysqli('localhost','root','password','books');
    
    if (mysqli_connect_errno()){
        echo "could not connect to database,please try again later.".mysqli_connect_errno();
        exit;
    }else {  
        $sql ="select * from books where".$searchtype."like'%".$searchterm."%'";
    
        $result=$db->query($sql);
        $num_result=$result-&gt;num_rows;
        for ($i=0;$ifetch_assoc();
            echo "<p>".($i+1)."title:";
            echo htmlspecialchars(stripslashes($row['author']));
            echo "Author:".stripslashes($row-&gt;newsauthor);
            echo "ISBN:".stripslashes($row-&gt;newsISBN);
            echo "price:".stripslashes($row-&gt;newsprice)."</p>";
        }
    }

    $result-&gt;free();
    $db-&gt;colse();
?&gt;
    

上述问题那微微大虾能给个解决方案！

------解决方案--------------------

PHP code

$sql ="select * from books  where  ".$searchtype."  like  '%".$searchterm."%'";

        if ($result=$db->query($sql)) {
            $num_result=$result->num_rows;
            for ($i=0;$ifetch_assoc();
                echo "<p>".($i+1)."title:";
                echo htmlspecialchars(stripslashes($row['author']));
                echo "Author:".stripslashes($row-&gt;newsauthor);
                echo "ISBN:".stripslashes($row-&gt;newsISBN);
                echo "price:".stripslashes($row-&gt;newsprice)."</p>";
            }
        }else{
            echo "fail.";
            exit;
        } <div class="clear">
                 
              
              
        
            </div>