php messaging problem

[azeem123456]

hi i am making content management system

so when i edit some subject  or i want to update subject if the subject update sucessfully it display msg subject update sucessfully i dnt know give any name to then it shud display error subject not updated

i have written code but it not working like supppose i want to change the name of subject previous it was hello if i remove hello and click on update button it should display error cant not update

in my script when i do this it just rremove the name its run update statement

this is my code kindly help me out

it doesnt shows errors msgs

query= "UPDATE subjects SET menu_name= '{$menu_name}', position ={$position}, visible ={$visible} WHERE id = {$id}";
$result=mysql_query($query,$connection);
if(mysql_affected_rows()==1){
	// sucess
	$message = " The subject was sucessfully updated";
}else {     //failed
	$message = " The subject  updated failed";
		$message .="<br/>".mysql_error();	
}


	}else {//error occur
	$message = "there were".count($errors)." errors in the form.";
	}




}//end of the if (isset(_spost)


find_selected_page();
include("includes/header.php");
?>      
		<table width="100%" id="Structure">
            	<tr>                	 
                   <td width="19%" bgcolor="#660000" id="nevigation">
<?php navigation($sel_subject,$sel_page);?>                    	
                    </td>
                    <td width="81%" bgcolor="#CCCCCC"id="pages">
                         <h2> Edit Subject:<?php echo $sel_subject['menu_name'];?></h2> 
					 <?php if(!empty($message))
					 { 
					 echo "<p class=\">" .$message ."</p>";
					 } ?>
                         <form action="edit_subject.php?subj=<?php echo urlencode($sel_subject['id']);?>"  method="post">
                         <p> Subject name:<input type="text" name="menu_name" value="<?php echo $sel_subject['menu_name'];?>" id="menu_name" /></p>
                         <p> position: <select name="position">
                         <?php $subject_set= get_all_subjects();
					 	$subject_count= mysql_num_rows($subject_set);
						for ($count=1;$count<= $subject_count+1;$count++){
						echo"<option value=\"{$count}\"";
						if($sel_subject['position']==$count){
							echo "selected";}
							echo ">{$count}</option>";
						}?>
                          
                         </select>
                         </p>
                         <p> visible : <input type="radio" name="visible" value="0"<?php if($sel_subject['visible']==0){echo "checked";}?> />No
                          
                         <input type="radio" name="visible" value="1" <?php if($sel_subject['visible']==1){echo "checked";}?> />YES
                         </p>
                         <input type="submit" name="submit" value="Edit Subject" />
                         </form>
                         <br/>
                         <a href="content.php">Cancel</a>

                       </td>
                     </tr>
                    </table>                       
				<?php require("includes/footer.php");?>