php - Can't seem to get query to work? -

<?php error_reporting(e_all);  session_start();  include ('connect.php');  if(!empty($_post['budgetbox'])) {     $budgetboxvar = $_post['budgetbox'];      $sql="insert users username = '".$_session['usernamebox']."'(budget) values ('$budgetboxvar')";       mysqli_query($db,$sql);    }  ?> 

does have idea why code above doesn't work ? seems code works if leave code below out. i'm sorry can't seem figure out how not correct ? i'm not getting error messages either.

when take out when username session usernamebox part out.. query input database, not in field of logged in user..

i tried echo if query succeeded doesn't show either.. means query can't executed (i think). can't figure out why though(it's hard being noob sometimes)

thank in advance, hope can !

if understand correctly, this:

 $sql = "update users set budget='".$budgetboxvar."' username = '".$_session['usernamebox'];