UPDATE statement not working

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PHP

MySQL

errors

I have a area where admin can change a users details or delete a user, the delete statement is working well, update on the other hand is not updating.

when i echo out the update statement I get :

UPDATE users SET username='superman', dob='0000-00-00', location='The Daily Planet ', group='2' WHERE id='136'

so I know the data is begin process correctly, its just not updating the data itself.

My update statment

require 'core/init.php';
$username = mysql_real_escape_string($_POST["username"]);
$dob = mysql_real_escape_string($_POST["dob"]);
$location = mysql_real_escape_string($_POST["location"]);
$group = mysql_real_escape_string($_POST["group"]);
$user_id = (int)$_POST['id'];

    $result = mysql_query("UPDATE users
              SET username='$username', 
                  dob='$dob',
                  location='$location',
                  group='$group'
              WHERE 
              id='$user_id'");

  echo  "UPDATE users
              SET username='$username', 
                  dob='$dob',
                  location='$location',
                  group='$group'
              WHERE 
              id='$user_id'"

    
            
	//header("location:admin.php");

To me this looks fine, but something it preventing the data entering the database.