สอบถามเรื่องการเชคค่าว่างจากการ fetch array และปัญหา rowspan

<table width="370" border="1" align="center">
<tr>
<td width="155" bgcolor="#FFFF99"><div align="center"><strong>Transponder</strong></div></td>
<td width="55" bgcolor="#FFFF99"><div align="center"><strong>Channel</strong></div></td>
<td width="60" bgcolor="#FFFF99"><div align="center"><strong>Active</strong></div></td>
</tr>


$sql_max = "SELECT MAX(`Id`) FROM `$tbl_name2`;";
$maxOfTransponder = mysql_query($sql_max);
for ($n = 1; $n < $maxOfTransponder ; $n++){ // for query by transponderid
	$sql = "SELECT * FROM `$tbl_name` where TransponderId = $n ; ";
	$result= mysql_query($sql);
 	
	$i=0; // This variable (i) will increase util no row selected
  	while ($row = mysql_fetch_array($result)) {
		
			$Col_ChannelName[$i]= $row["ChannelName"];
			$Col_Active[$i]= $row["Active"];
			$i++; 
	
	
		}
	
?>


<tr>
<td bgcolor="#99CCFF" rowspan="<? echo $i;?>"><div align="center"><strong>Transponder<? echo $n;?></strong>
</div></td>

<td>

	<div align="center">
	  <table border="0">
	    <? for ($j=0; $j<$i; $j++){ ?>
	    <tr> 
	      <td><? echo $Col_ChannelName[$j]; ?> </td>
	      
	      </tr>
	    
	    <? } ?>
	    </table>
    </div></td>
<td>

	<div align="center">
	  <table border="0">
	    <? for ($j=0; $j<$i; $j++){ ?>
	    <tr> 
	      
	      <td><? echo $Col_Active[$j]; ?> </td>
	      </tr>
	    
	    <? } ?>
	    </table>
    </div></td>
</tr>



<? } ?>
</table>