[support] How can I get the error message from database

[robert mena]

For some reason one of my queries is not executing.  I've used the
db_error() but I only get 0.    I'd like to know how can I get the
error message.

I am using drupal 6, MySQL.

$success = db_query("INSERT INTO {user_profile_fields} (uid, username,
id_center, telephone, street, city, distt, country, zip) VALUES
('$uid', '$username', '$idcenter', '$telephone', '$street', '$city',
'$district', '$country', '$zip')");
  if(!$success) {
     // here I am using the $error = db_error();
  }

Regards.