mysql query executed even though fields are empty

Question

I have created a simple tagging system for my schools websites for the students. Now the tagging system is working perfectly now i also have to save tags in a notifications table with respective article id to later notify the students which article they have been tagged in even that i managed to do. But now if by chance you want to remove the tags sometime realizing while typing the article you don't need to tag that person, then the first put tag also gets updated in the db.

//ajax code (attach.php)

<?php
include('config.php');
if(isset($_POST))
{
$u=$_POST['v'];

mysql_query("INSERT INTO `notify` (`not_e`) VALUES ('$u')");
}

?>

// tagsystem js code

<script type="text/javascript">
var id = '<?php echo $id ?>';
$(document).ready(function()
{

var start=/%/ig;
var word=/%(\w+)/ig;

$("#story").live("keyup",function() 
{
var content=$(this).text();
var go= content.match(start);
var name= content.match(word);
var dataString = 'searchword='+ name;

if(go.length>0)
{
$("#msgbox").slideDown('show');
$("#display").slideUp('show');
$("#msgbox").html("Type the name of someone or something...");
if(name.length>0)

{
$.ajax({
type: "POST",
url: "boxsearch.php",
data: dataString,
cache: false,
success: function(html)
{
$("#msgbox").hide();
$("#display").html(html).show();
}
});

}
}
return false();
});

$(".addname").live("click",function() 
{
var username=$(this).attr('title');
$.ajax({
type: "POST",
url: "attach.php",
data: {'v': username},
});
var old=$("#story").html();
var content=old.replace(word,""); 
$("#story").html(content);
var E="<a class='blue' contenteditable='false' href='profile2.php?id="+username+"'>"+username+"</a>";
$("#story").append(E);
$("#display").hide(); 
$("#msgbox").hide();
$("#story").focus();
});
});
</script>

Answer 1

Looks like your problem appears on the if statement in php code: even though $_POST['v'] is empty and the sql still get excuted.

There is the quote from another thread:

" Use !empty instead of isset. isset return true for $_POST because $_POST array is superglobal and always exists (set).

Or better use $_SERVER['REQUEST_METHOD'] == 'POST' "

Or in my opinion. Just put

if ($_POST['v']){
    //sql query
}

Hope it helps;)

Answer 2

 <?php
include('config.php');

 $u = $_POST["v"];

 //echo $a;


  if($u != '')
   {

    mysql_query("your insert query");
  }
   else
       {
       }



 ?>