title: Laravel query returns unexpected order
body: <p>I'm using Laravel Query Builder to get a set of rows, ordering them by 2 columns, <code>ticket_id</code> then <code>id</code> (previously <code>created_at</code>). However the result orders them by <code>ticket_id</code> (correct), but the <code>id</code> (or <code>created_at</code>) secondary order is incorrect. Am I approaching this wrong, misunderstanding ordering?</p>
  
  <p>Here's my query:</p>
  
  <pre><code>$responses = Response::where('status', '=', 'closed');
                         -&gt;select('id', 'ticket_id', 'created_at', 'author_id')
                         -&gt;orderBy('ticket_id', 'id')
                         -&gt;get();
  </code></pre>
  
  <p>Which in turn, returns:</p>
  
  <pre><code>  0 =&gt; array:3 [
      "ticket_id" =&gt; 14
      "id" =&gt; 71
      "time" =&gt; "2018-05-25 08:55:03"
    ]
    1 =&gt; array:3 [
      "ticket_id" =&gt; 14
      "id" =&gt; 75
      "time" =&gt; "2018-05-25 12:48:45"
    ]
    2 =&gt; array:3 [
      "ticket_id" =&gt; 14
      "id" =&gt; 72
      "time" =&gt; "2018-05-25 08:55:53"
    ]
    3 =&gt; array:3 [
      "ticket_id" =&gt; 13
      "id" =&gt; 70
      "time" =&gt; "2018-05-25 08:53:50"
    ]
    4 =&gt; array:3 [
      "ticket_id" =&gt; 13
      "id" =&gt; 76
      "time" =&gt; "2018-05-29 12:30:46"
    ]
    5 =&gt; array:3 [
      "ticket_id" =&gt; 13
      "id" =&gt; 74
      "time" =&gt; "2018-05-25 11:30:36"
    ]
  </code></pre>
  
  <p>You see for ticket 14, the order is 71, 75, 72, rather than 71, 72, 75.</p>
  
  <p>Here's the table structure too:</p>
  
  <pre><code>+------------+------------------+------+-----+---------+----------------+
  | Field      | Type             | Null | Key | Default | Extra          |
  +------------+------------------+------+-----+---------+----------------+
  | id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
  | ticket_id  | int(11)          | NO   |     | NULL    |                |
  | author_id  | int(11)          | NO   |     | NULL    |                |
  | status     | int(11)          | NO   |     | 0       |                |
  | content    | text             | NO   |     | NULL    |                |
  | created_at | timestamp        | YES  |     | NULL    |                |
  | updated_at | timestamp        | YES  |     | NULL    |                |
  | assets     | text             | YES  |     | NULL    |                |
  +------------+------------------+------+-----+---------+----------------+
  </code></pre>