php-mysql查询删除项目，即使该项目不在表中 - php mysql query deleting items even when the item is not present in the table

php mysql query deleting items even when the item is not present in the table

这是我的"从图书馆页面删除书籍"

<HTML>
     <?php
        global $bkiderr;
     ?>
    <link rel="stylesheet" href="btndeletebooks.css">
    <link rel="stylesheet" href="tablealncenter.css">
    <link rel="stylesheet" href="spanerror.css">
    <p><span class="error">* required field.</span></p>
    <HEAD>
        <h1 align="center">THIS PAGE REMOVES BOOKS FROM THE LIBRARY</h1>
    </HEAD>
    TO REMOVE BOOKS FROM THE LIBRARY<BR><BR>
    <FORM action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" method="POST">
    <table>
        <tr>
             <td>ENTER THE BOOK ID &nbsp;(format -> bkyearbkno ) :</td>
             <td><input type=text name="bkid">
             <span class="error">* <?php echo $bkiderr;?></span>    
        </TR>
    </table>
     <BR>
     CLICK HERE TO REMOVE BOOK:
     <table> 
     <tr>
         <td><input id="rndbutton1" type="submit"  value="REMOVE BOOK FROM LIBRARY" name="submit" title="CLICK HERE TO REMOVE A BOOK"></td>
     </tr>
     </table>
     </br></br>   
    </FORM>
    <?php
        include 'dbcon.php';
        $qbkname="select bkname from books where bkid=";
        #-------------------------REMOVE BOOKS FROM LIBRARY-----------------------#
        if( $_SERVER["REQUEST_METHOD"] == "POST")    
        {
            if (empty($_POST["bkid"]))                       
                $bkiderr="BOOK ID is required";
            else
                $bkid = $_POST["bkid"];
            if(isset($bkid))
            {
                $qchkissuestat="select * from books where bkid='$bkid'";
                $reschkissuestat=$mysqli->query($qchkissuestat,MYSQLI_STORE_RESULT);
                while($res=$reschkissuestat->fetch_array(MYSQLI_NUM))
                {    
                    $k=$res{5};
                    echo $res{0}." ".$k."'n";
                    break;
                }    
                if($k='YES')
                {
                    $query="delete from books where bkid='$bkid'";
                    $result=$mysqli->query($query,MYSQLI_STORE_RESULT);
                    echo "YOU REMOVED THE BOOK FROM THE LIBRARY";
                    echo "<table border='1'>";
                    echo "<th>BOOK ID";
                    echo "<tr>";
                    echo "<td class='alncenter'>$bkid</td>";
                    echo "</tr>";
                    echo "</table>";
                    exit();
                }    
            }
        }
        $mysqli->close();
    ?>
     <div class="error">
        <?php
            echo "$bkiderr    <BR>";
        ?>
     </div>
</HTML>

这个页面上的代码是删除作为图书id提供的图书，即使没有指定图书id作为输入的图书，我也不希望这样。在从表中删除项目之前，我需要一种机制来检查表中是否存在特定的图书id。

首先更正语法：

if($k='YES')

应该是

if($k=='YES')

通过检查$bkid的值

print_r($bkid);

或

var_dump($bkid);