Query custom field on user table
Entity fields are in their own separate table(s), they don't get attached to the base entity table.

You can use an EntityFieldQuery to get that data:

$query = new \EntityFieldQuery();
$query-&gt;entityCondition('entity_type', 'user')
  -&gt;fieldCondition('field_display_name', 'value', 'bubba');

$results = $query-&gt;execute();
if (!empty($results['user'])) {
  $users = user_load_multiple(array_keys($results['user']));
}


See Where does Drupal 7 store custom user account fields? for a bit more info