rangking siswa

<?php
    $id_kelas=$_POST['kelas'];
    $id_ajaran=$_POST['ajaran'];
    $no=0;
    $a=0;
    $b=0;
    $c=0;
    $v=0;
    $y=0;
    $z=0;
    $f=0;
    $g=0;
    $h=0;
    $p=0;
    $e=0;
?>
<?php
$sql =" select * from tb_detailkelas
            where id_kelas='$id_kelas' and id_ajaran='$id_ajaran'";
            $hasil = mysql_query($sql) ;//or die ("Kesalahan pada perintah SQL!");
            echo mysql_error();
            while ($data=mysql_fetch_array($hasil)){
        ?>
            <tr>
                <td><?php   $no; ?> </td>
                <td><?php   $data['nis']?></td>

            </tr>
<?php
$test=$data['nis'];
$no++;
$sql1 =" select * from tb_rapot
where nis='$test' and id_ajaran='$id_ajaran' order by nilai_rapot desc";
    $hasil1 = mysql_query($sql1) ;

    echo mysql_error();
    while ($data1=mysql_fetch_array($hasil1)){
    ?>
    <tr>
        <td><?php   $no; ?> </td>
        <td><?php   $data1['nis']?></td>
        <td><?php   $data1['nilai_rapot']?></td>

    </tr>
    <?php
            //$e1=$data['nis'];
            $d=$data1['nilai_rapot'];
            //var_dump($d);
            if      ($a=0){$a=$d; $f= $data1['nis'];}
            else if ($b=0){$b=$d; $g= $data1['nis'];}
            else if ($c=0){$c=$d; $h= $data1['nis'];}
            else if ($d>$a and $d>$b and $d>$c ){ $a=$d;  $h= $data1['nis'];}
            else if ($d>$a and $d>$b and $d<$c ){ $b=$d;  $g= $data1['nis'];}
            else if ($d>$a and $d<$b and $d<$c ){ $c=$d;  $f= $data1['nis'];}
        }

    }


?>


<?php
if($a>$b && $a>$c){$y=1;}
else if($b>$c){$v=2;}
else{$z=3;}
?>
<td>NIS:<?php echo $h; ?> </td><td>rangking :<?php echo $y; ?></td>
<td>NIS:<?php echo $g; ?> </td><td>rangking :<?php echo $v; ?></td>
<td>NIS:<?php echo $f; ?> </td><td>rangking :<?php echo $z; ?></td>