Multiple warning mails sent per day in certain condition

For Drupal running over PostgreSQL, I've found that on certain conditions the expiration warnings are sent multiple times.

This seems to depend on the way password policy get the data from the database in the function password_policy_cron() in password_policy.module:561:

  // Get all users' last password change time. We don't touch blocked accounts.
  $query = db_select('users', 'u', array('target' => 'slave'));
  $query->leftJoin('password_policy_history', 'p', 'u.uid = p.uid');
  $query->leftJoin('password_policy_expiration', 'e', 'u.uid = e.uid');
  $result = $query->fields('u', array('uid', 'created'))
    ->fields('p', array('created'))
    ->fields('e', array('pid', 'unblocked', 'warning'))
    ->condition('u.uid', 0, '>')
    ->condition('u.status', 1)
    ->orderBy('p.created')
    ->execute();

This code results in the following query:

SELECT u.uid AS uid, u.created AS created, p.created AS p_created, e.pid AS pid, e.unblocked AS unblocked, e.warning AS warning
FROM 
drupal_users u
LEFT OUTER JOIN drupal_password_policy_history p ON u.uid = p.uid
LEFT OUTER JOIN drupal_password_policy_expiration e ON u.uid = e.uid
WHERE  (u.uid > 1) AND (u.status = 1) ORDER BY p.created;

This query will not produce the expected results in every situation. For example, I report the last lines for an user in our database:

 uid |  created   | p_created  | pid | unblocked |  warning   
-----+------------+------------+-----+-----------+------------
  92 | 1424875056 | 1473749500 |     |           | 1481108701
  92 | 1424875056 | 1473749500 |     |           | 1480247401
  92 | 1424875056 | 1473749500 |     |           | 1480243801
  92 | 1424875056 | 1473749500 |     |           | 1438788782
  92 | 1424875056 | 1473749500 |     |           | 1438810385
  92 | 1424875056 | 1473749500 |     |           | 1481105101
  92 | 1424875056 | 1473749500 |     |           | 1480240201
  92 | 1424875056 | 1473749500 |     |           | 1438828382
  92 | 1424875056 | 1473749500 |     |           | 1480236601
  92 | 1424875056 | 1473749500 |     |           | 1438795982
  92 | 1424875056 | 1473749500 |     |           | 1452877718
  92 | 1424875056 | 1473749500 |     |           | 1480233001
  92 | 1424875056 | 1473749500 |     |           | 1452527842

As you can see, the results are only ordered by p_created column. We need to order them also for the warning column, to obtain the last time a expiration warning was sent for the user.
In the above situation, if the cron run more than a time during the day, the expiration warning is sent more than once.

The proposed solution is to add the column e.warning for ordering the mentioned query.

  // Get all users' last password change time. We don't touch blocked accounts.
  $query = db_select('users', 'u', array('target' => 'slave'));
  $query->leftJoin('password_policy_history', 'p', 'u.uid = p.uid');
  $query->leftJoin('password_policy_expiration', 'e', 'u.uid = e.uid');
  $result = $query->fields('u', array('uid', 'created'))
    ->fields('p', array('created'))
    ->fields('e', array('pid', 'unblocked', 'warning'))
    ->condition('u.uid', 0, '>')
    ->condition('u.status', 1)
    ->orderBy('p.created, e.warning')
    ->execute();

Regards,